Do I need to bore the engine, or can I hone and use the stock pistons?
 

On my last 400 engine, I blew my allowance and went full tilt on the rebuild. I was biting my tongue in anticipation of doing it again, but had something interesting happen on my current project.

I tore down a stock 68 400 YT engine yesterday to send it in for machining. I bought this engine a long time ago and it just sat in my garage with oil that I had squirted into the cylinders through the spark plug holes.

I don't have much info on the engine, but the guy I bought it from said it ran good and he thought it wasn't ever cracked open. To my surprise, when I removed the heads, the oil I squirted into the cylinders was still there. All of the cylinder walls looked very nice and of course were were smooth. I checked the pistons and they had no size indication on them, so I then did a quick check on two of the cylinders. Indeed, the block was never bored. I have yet to do a full check on how much wear there is on both the pistons and cylinders, but this got me to wondering. How much wear is acceptable to just do a hone and ring job and then reuse the stock factory pistons? Mind you, the car is only for summer shows and crusing. I just want it to run good.

It might sound silly to do a rebuild without replacing everything, but back in the day I did it several times and it worked just fine. Bye the way, the crank looks excellent and bearings were still the stock GM bearings. Still need to check it for wear as well.

Old Joe

Just Hone it out, Valve job it, re-ring kit and CLEAN everthing the best you can.......
It wont go 100,000 miles
But still should be a good Full rebuilder....some time in the future when you can, do it correct.
"Just like back in the DAY"

If you want it for cruise in duty and weekend driving in the summer on a tight budget, do a "backyard rebuild" on it like w.e used to do 40 years ago. Strip the block bare, roll it outside and run a ball hone through it about 15-20 strokes each cylinder, keeping the hone very wet. 280 grit. Buy some Hastings or equivalent PLAIN IRON piston rings. They are very soft and will give you the best chance of having a successful break-in. Get new bearings, freeze plugs, full gasket set. Clean everything to death, using laundry detergent, lots and lots of scalding hot water. Blow everything dry and throw it back together. It will likely run decent, probably better than 90% of the Barret Jackson cars. Expect it to last 30-50K miles before it begins to wisp some smoke and burn some oil. That is 10-15 years for most collector cars. Can do the entire deal for less than $1000.00 on a typical Pontiac V-8. That includes a new timing set, rings and bearings, oil pump, gaskets, plug kit, cam and lifters.

Or you can really do it right for 5-7K. Or anything in between.

I bought a '66 389 in similar condition. It was in a field installed in a rusty '65 GTO. It ran so good with a gas can attached that even the choke kicked down once it warmed up. No smoke and no fouled plugs.
I pulled the heads and had a valve job done and took it to a machinist friend of mine to check the short block. Said it just needed a hone so that's what he did. I had him install the cam and main bearings and rear main seal. Re-ringed it added new rod bearings and all the peripherals... it's been in a plastic bag ever since.
Funny, I just fogged the cylinders and turned it over a few times yesterday. It'll be quite some time before it winds up in a car so I left the valley plan unsealed and the intake off so I can get back into it and make sure everything is still lubed up as far as the camshaft goes.

Yup, I did quite a few cheapo rebuilds and only a few where I spent the loot to do it "the right way". All of them ran. In fact, some of the cheapo builds ran extremely well. Still, I would like to know what the wear specs are for simple honing and re-ringing. Back in the day when I did it, the engines were much younger and had less than 100K miles on all of them (just like me). Since I don't know the history of this engine, I don't want to assume that ringing it without making sure it is in reasonable tolerance will produce good results.

I guess this engine is kind of like me. Old and needs some love, but won't get many miles put on it.......................... :rolleyes:

When I blew up the motor in my 76 formula, I got a junkyard 400 from an old Pontiac wagon. Tore it down, cleaned it up, did all the things that mgarblik mentioned, put it back together with the original pistons and drove the car as a DD for about a year when I sold it to a friend who I know drive it for at least 3 years as a DD. There was nothing high performance about that motor but it ran good as a DD for probably at least 40k miles, maybe more.

And In fairness I should add that I have no idea how mine is going to run. I'm not an engine builder by any means.

Here’s what the factory wanted for piston to wall clearance.
As you can see as the compression went down and the exh gas temps went up the engineers wanted more piston to wall clearance.

I would suggest to you that since you are saving money with your rebuild by not boring, that you put a bit more back in by getting a Total seal gapless top ring and then run a reverse twist barrel face moly second ring like the motor came out of the factory with.

The moly face top and second ring are why Pontiac cylinder walls last so long.

Be sure to take the hours that it will to break / lightly roll over all the 90 degree corners on all the rings .
This will stop these edges from digging into the walls and scratching them and also digging into the pistons.
Besides being rewarded with having no added ware taking place to the cylinder walls you will also have less friction and cooler water temps.

The ends of the oil ring rails being that they are hard steel are a big culprit in the scratches seen on cylinder walls.
If you do any rolling over of the corners of any of the rings then it should be these.

The thing about these old engines people forget is there is no diagnostic system turning on the "check engine" light for any one of 700 miniscule little problems. If you use soft piston rings to conform to the worn, tapered and out of round cylinders, lap the crap out of the valves so they have a complete mating surface and put new valve seals on, as long as the camshaft still has some bumps on it the engine will run. I had a student leave ALL the piston rings off a Honda B series 4-cylinder engine and put it back in the car. The piston to wall spec. is so tight the stupid little engine started and ran with no piston rings. Once it warmed up is ran terrible and began smoking. But it started and you could drive it. Backyard overhaul on a factory 350 HP 400 will probably make 300-320 HP with a quick ring, hone and lap job.

Check the taper in the bores and if not bad do what Mike Garblik said in post #3. The engine I've been flow testing carbs on for twenty years came out of a '61 Catalina more door I parted out. It had 80k miles on it and .003 or less taper in the bores so I did that rebuild on it but with an 068 cam and it has been a dependable little engine for almost nothing.

Thanks for the spec info. This reminds me of something I learned with my last engine. Originally I had it bored for 30 over pistons. The shop that did it cut and honed the cylinder walls for something other than the Old School TRW Forged Pistons I was using. I had those things in storage for 25 years waiting for the build! In the end, I had to have the block rehoned a few thousanths larger. The point I'm making is that forged pistons require a larger bore size (as shown in the chart your provided). If I could magically locate an old school set of standard size forged pistons, they might be a good match for this build. Of course, I haven't even checked out the bore size and taper yet so this is all just wishful thinking.

OJ

Thousands of years ago, I was in Trade School. We were told that .007 taper was the absolute limit, and only for a "grandma goes to church" engine--nothing with any performance aspirations.

The "Service Limit" for the 350 in my '88 K1500 was .001 taper. My replacement block had about .0015, I put it together and it's working fine.

There is no way I'd use plain iron rings. Inexpensive Moly-faced are as cheap as I'll go. Moly is porous, holds oil, reduces cylinder wall wear AND seals better.

Most pistons are supposedly set up with the clearance built-into the piston--you'd hone to the nominal bore size, and the piston would be appropriately smaller to give correct clearance.

But I won't guarantee that all pistons are made that way. My favorite machinist wants to have the pistons in-hand so he can measure them before honing.

Rigid honing should be done with a torque plate. Dingle-berry brush honing won't need a torque plate.

Don't forget to plane the head gasket surfaces square to the crank, and to end-up with appropriate quench/squish given the compression height of the pistons you select.

I don't understand how we got into the subject of forged pistions and the clearances needed for such when it seems you have a good stock usable Bore with stock cast factory pistions.

What am I missing here?

Ball hone it , wash it out 3 times over, clean out any crap in the ring grooves with the tool you can buy for that then re-ring it and have good summer fun with it.

Also please note that when your running a cylinder Bore that likely has a taper to it and will be a tad oversized after the honin, then you do not want to run a plain iron compression ring, you want a ductile iron ring.

The flexing that the rings experience by the out of spec Bore will quickly fatigued a plain iron ring and reduce its outward tension needed to seal.
A ductile iron ring will hold up far longer in a used Bore .

Here's the problem with the hone-ring thing.

Cylinder walls wear tapered, less at the bottom and more up where the heat is. This "works" the rings too much if there is taper in the bores and they loose their tension quickly. Second problem is the top ring land in the pistons. They wear a LOT faster than the lower ring land leaving the ring loose and it flutters all over the place.

So, IF your bores are straight and piston ring lands tight nothing at all wrong with honing the block and installing new rings. Piston skirt to bore should be fine as that's seldom an area of concern but common sense still applies here they have to be tight on the bores over everything rocks around too much and it will wear out quickly.

Basic rule of thumb is to look at the "ridge" at the top of the cylinders. If none present you are tyipically looking at a lower mileage well cared for engine that didn't get a lot of dust/dirt ran thru it. Those make for excellent re-ring jobs in most cases. If you find a lot of ridge at the top of the bores you don't need a qualified machine shop to tell you it needs bored to the next size.

Same with crankshafts. Most to NOT need much more than polished if the engine was running fine when removed from the vehicle. WIth split precision bearings the bearings never touch the crank so most are in really nice shape if the engine was well cared for and didn't grind up a cam lobe and pump millions of metal particles thru it. Once again common sense applies here and if the bearings look good, crank isn't all scratched up and tore to hell you are good to go there as well.

Valve guides are often in perfect shape with Pontiac heads as they use low lift cams and gentle lobes without a buttload of spring pressure. Still need to be checked to make sure they are really tight. If so you can simply "touch" up the seats, surface the valves and back in business. I always replace the valve springs vs shimming old ones, but will re-use Pontiac retainers and keeps every single time, they are very strong parts. So are the rocker arms and pushrods and can go right back in if not heavily worn anyplace.

Cams and lifters are risky to use again, but then we have all this outsourcing with those parts these days so it's a crap shoot to get good USA made parts to replace them. As for oil pumps and timing sets I always put a new Melling pump back in place, but NEVER just drive the pick-up on it and think it's good to go. This new metal doesn't have any "memory" and you've got to take an extra step to retain the pick-up on the pump or it's coming off after you run the engine in.

As for timing sets I use and prefer the stock 3/4" wide Morse chain set-ups. They are at least 5 times stronger than a cheap double roller variety and will last the life of the engine. The high-end billet double roller stuff is OK, but I've seen enough failures with them in high mileage engines that I woln't use them here for that sort of work. They do make the cam easy to degree and fine for most of these engines based on the way the vehicles are typically used. Most are lucky to see 1000 miles in the next 10 years so using a junk bicycle chain set-up to drive your camshaft isn't really much of a concern and we don't hear about how bad many of those parts really are.......FWIW......

PS: I'm pretty sure I have a Speed Pro stock bore ring set in the parts room. I'm doing a MAJOR shop clean-up and have been scrapping all sorts of parts.

Tried selling some but folks on the websites are like black birds picking corn out of cow poop, plus shipping is expensive, taking pics and advertiseing time consuming and eating into my retirement fun. I don't have time for all that so just throwing most of what's left in the scrap pile instead.

If they are still out there I'll run them for sale again, cheap.....

Steve,

The engine is a stock bore, but I have not yet measured the individual bores for wear in any way. I mentioned that, but perhaps you missed it. If the bores and pistons turn out fine, then yes, I probably will go with a re-ring. but if it turns out there is too much wear, then I have to go another route on this build, hence my comment about wishful thinking and forged pistons.

I started the thread asking a simple question about what acceptable levels of wear are for a ring job and that's really all I was looking for. While I'm no where near the level of engine builder as many folks on this string, I've done around a dozen engines, but that's over nearly 50 years and not all of them were Pontiacs so I have a lot to learn in my retirement.

Now if I could only remember how many molecules in a mole.

OJ



.

That is an easy one: 6.022*10^23


:)

Back about 50 years ago when you would only put about 10,000 miles a year on your only auto, we would put Hastings rings on anything with about .003 taper. If the cylinders were tapered more we would think bout using Continental rings. Continental had some interesting oil control rings. The rebuild would last a couple years and that would be it. I used some Hasting rings on a re-ring on my spare 400. It ran great but I only had it in for about 7000 miles before I went with my .030 over 455.

With all of this fine advice, I checked the taper on the cylinders. As Cliff noted, engines with little ridge on the cylinders are often lower mileage engines and make for good re-ring jobs. This engine had by far the smallest ridges on the cylinders of the Pontiac engines I've done. The taper came out very nice. Two of the cylinders had .0015 taper and all the rest were less than that, so the wear was very even. Still need to check the pistons and crank. I expect the crank to come out fine as the bearings have nice even wear that's not excessive and the crank looks great just eyeballing it. Not sure how the pistons will come out. Crossing my fingers.

OJ

Check the original pistons very carefully for cracks in the ring lands. Almost sprung for a re-ring job cause the bores were still decent but after another careful inspection i found three cracks on no. 7 piston. So since i had to buy new pistons anyway, i went ahead with .030 overbore and forged pistons. Some of the cracks are really hard to see. I used a magnifying glass to spot. From now on i run octane booster and 93 gas.

As Cliff has said, the ridge is a great indicator on cylinder wear. Pontiac blocks stand up well to wear, if they were taken care of.

I have re ringed a lot of 400s 428s and 455s and run them at stock bore with the cast pistons they came with. I still own a standard bore, low mileage 428 that I ran in the 69 Grand Prix race car in my third signature pic, it has TRW forged pistons in it, still ran fine when removed from the race car after 3 seasons.

When I was racing dirt track cars we had a claimer rule on the beginner class cars of $225, meaning a competitor could buy your car if you won 3 races in a row (1975 thru 1982 time period). Obviously with the rule you didn't want to infuse a ton of money into the car, or engine, so I did a lot of engines with just a hone, new rings and bearings, good oil pump and a 068 cam and new lifters, and a fresh valve job, although if the valve seal was good, sometimes not even a valve job.

I did engines for myself, as well as people I sponsored having owned a business at the time. So I did a good deal on Pontiacs with standard bores, stock pistons, and rods. They survived very well in that environment, and as my signature pictures show, I did quite well in my racing career.

When I retired the car in the second picture the engine was sold, and went into a 68 Firebird street car. That engine had 2 full seasons of racing on it. Years later I happened to run into the guy, and he still had the car, but had taken it off the road due to rust issues. He said the engine still ran well, and was looking for another car to put it in. That answers the longevity question.

The engines I built won a lot of races over the time they were in race cars. These engines had acceptable blow by, didn't use oil, and had good power. Overheating them repeatedly though, would ruin the ring seal quickly. Maybe my experience with re ringing a standard bore Pontiac will hopefully give you some insight.

OJ - I'm sure many will disagree with me, but from what you have described I would be tempted to just clean and reassemble the engine then see how it runs. Assuming your inspections find nothing wrong of course. Are the pistons still in the bores?

Might waste some time but it also might be just fine. Doesn't sound like you are going to pound on it or huge miles so what would be wrong about having a survivor 1968 YT engine?

Barry

The pistons are all out of the engine now so I can inspect them.

One issue is that you can visibly see the coating on the cam bearings flaking off in some spots. I want to hot tank the block, so it would get new cam bearings anyway. I suppose I could just install new cam bearings myself, but I'm not up for a degrease fest anyway so it's going into the shop either way.

From all of the replies I received on this, it just goes to show that I wasn't alone in putting things together without big money in my earlier days.

I find it quite interesting to see the range of replies I received and the rationale supporting peoples comments. I'm afraid that my modest opening question led people to believe I was trying to do this with almost no budget. That's simply not true, but what I'm waking up to is that I don't need to build a big dollar engine when it will only see light use and not many miles. I can then use the money I've saved to get one of those Elon Musk brain chips.

I wasn't really thinking about budget, it was just keeping known good original parts. Assuming of course that they pass inspection.

One more update. I spent a good deal of today cleaning up the mess I made in my garage and putting things away. During the first part of last winter I repainted the plaster walls and updated the lighting, while adding some nostalgia artwork. It bothers me when I go from being fussy about the looks of the garage to creating a sludge fest.

Anyway, I examined the head gaskets and they look original to me so I cleaned some of the sludge off and sure enough, there was a GM logo and part number 9790910 on the gasket and on the end of the gasket VIC-2-POLD. I believe GM used more than one supplier, but kept the same part number. I'm thinking the VIC-2-POLD means it was a Victor Reinz gasket. If anyone can confirm that, I would find it interesting. Tomorrow I will hopefully have time to examine the pistons.

Also, how / where did GM mark the cams? No question, this one is worn and so are lifters. The cam timing gear looks to have been replaced with a sintered metal gear and the chain had a lot of slop in it.

OJ

In the second paragraph of your first post here you stated that you sent the motor in for machining, so how can you be inspecting the block and cam bearings?

I don’t get it!

Well In fairness he did not say that he sent it in, he said that he tore it down TO send it in.

Victor, and Mc Cord made most of the GM head gaskets from memory. I used to work for the Pontiac dealer when I had just graduated from high school/Vo tech.

I always bought my engine gaskets from The dealer because I could buy only what I needed, and it was cheaper. From formerly working there I knew the parts manager, he took good care of me. When I had my garage I always kept some gaskets in stock, because I specialized in repairing, and modifying Pontiacs.

GM marked the cams usually with single letters on the nose of the cams, older ones had numbers also. Here is a listing on Wallace racing supplying the codes:

http://wallaceracing.com/camcode1.htm

Pontiac marked the front of the cams, aftermarket usually marks the rear. I'm guessing the person assembling the retainer, and timing gears could just glance at the front of the cam while it was in the engine to confirm what cam was installed.

Thanks for the confirmation on the head gaskets.


The front of the cam is marked 524009. Looking at the Wallace Racing site, it seems this might be from a 64 GTO or a 421 engine and not native to this engine. I would not find that hard to believe. The cam is quite worn on the lobes and the lifters are very worn as well. Perhaps they were used when installed????? Also, some of the cam bearings have the silverish coating sort of chipped at the front and back of the bearings. I thought this was from wear, but perhaps it's from someone installing a cam and being a bit careless. Does that make sense? It's only the edges of the bearings that have this issue, so I'm thinking it's from catching the edge when installing / removing the cam. The cam timing gear was certainly replaced as it isn't original.

OJ

Keep in mind that the "norm" back in the day was to do the bare minimum required to keep the engine in operation. Not uncommon to see used parts in it, top timing gear replaced as some of the OEM's had plastic coated top gears, etc. Most folks back when I started in this hobby had to fart in their pocket to have a cent.

When something went wrong or prevented the vehicle from being used out comes the duct tape, super glue, rubber bands, bailing wire and JB Weld to hold it together so we could keep driving. Hiring machine shops to bore, deck/square, balance, install valve guides, etc was absolutely OUT of the question for most enthusiasts, unless your dad was the CEO of a big company, which didn't happen in my neck of the woods as just about everyone came from a dirt poor farm or their dad worked on an assembly line at a local factory, or self employed in some sort of construction job.

I owned a ridge reamer, hone, cam bearing install tool and a ring compressor. I did the poor mans "rebuild" on scoores of these engines. I remember going to the local junk yard and pulling heads from SBC and 440 Mopar engines just to find a set that didn't need valve guides as I couln't afford to have them installed. I used lapping compound and an old Sears Craftsman drill on the stems to grind the valves into the seat to get a decent seal.

These days we've got a little more money to work with and have learned enough hard lessons from way back then to do a little better job with these things.

As mentioned in my first post your enemy here is tapered wear in the bores, out of round, and wear in the upper ring land in the pistons. Those are the death sentence for a "re-ring" job as the pistons moving up and town 20-40 times a second just works the rings too hard to get any life out of them. If things are tight in those areas nothing at all wrong with going in with a hone to scratch things up some and stuffing some new rings on the pistons. I go just plain cast iron so they get a good bite and medium grit stones on your hone. In most cases it's seal right up and last quite a while.

For the crank just take an old boot lace and wrap it with 600 grit auto body paper and a quick polish on the journals to remove any high spots or minor scratches. Make sure the thrust is tight on assembly, and for sure pound some new cam bearings and freeze plugs in it. A new timing set is a must, Dyna Gear, Melling, Cloyes stock 3/4" wide sets all have metal gears these days and my first choice for one of these builds. They still have USA made Morse chains as well, at least the last time I looked at one which was about a year ago.

The cam and lifters will be the sore spot. So much re-boxing going on you're likely to get SE Asian junk even if it shows up in USA labeled boxes. Flip them over and "Country of Origin" listed on the bottom ranging from India, Taiwan, Mexico, China and half a dozen others just to confuse the buyer. That's be the deal breaker with your "low end" rebuild, gettign a good USA made cam and lifter set........IMHO........

Yup, I grew up in a small town of 12,000 people and like 90% of the people there, I had just enough money for beer on the weekends. My wife's engagement ring came from JC Penney and it was about $125! I remember doing a rebuild on an engine for my Camaro in the 70s and I couldn't afford a piston ring expander or compressor, nor could I afford new pistons. I scrounged enough for rings and bought some used forged pistons from a guy who raced the local 1/4 mile oval. I remember installing the rings on the pistons with my bare hands and then managed to make a ring compressor from an empty can that I cut vertically with a couple of band clamps on the outside of it. It took all day to get the pistons installed because the rings kept popping out of the end of my homemade tool. When it came to installing the engine, I made a structure out of 2 x 4s and had a $12 buffalo brand come along that I got on clearance. In the end, the engine ran pretty dang good.

I'm not a rich man, but as the song goes today.......... "I have more than I could ask for". Like so many people on this forum, I had to work for it and life really is good in my retirement. How in the heck could our country have moved from a system where everyone that works hard has a shot at a good life to where we are today? But I digress......... Got to go and check out the pistons today. We'll see how this goes.

I don’t have a lot to add too any of the comments. .005” bore taper is kind of my max that I will consider a rering. More than .005” across all holes or higher it needs bored. With .003” to .005” hold the RPMs to 5000, 5500 max. When he have tried too turn engines with that much bore taper past 5500, via bigger cam or better heads…we pretty much always made them slower. Under boost we pushed past that, I think the turbo compensated. NA with bore taper hurts top end power.

I have had more issues from freshly bore engines with new oversized pistons (and not bore with a tq plate) than a rering OEM seasoned engine.

On a low compression engine for a rering I will use moly rings. On high compression pump gas we prefer too use a cast type ring, like mentioned in that post Mike did in post 3. Or something that is both resilient and can take heat on the top ring, and a moly ring on the second. Best of both then. The cast hold up better with extra heat (like preignition) than the moly. We have had trouble with the moly rings loosing there tension more than cast rings. I have peeled some off the piston like a piece of wire. The moly rings on the top ring, can seem to work harden quicker if it is a high compression engine with bore taper. The bore taper is always the worst at the top of the cylinder were the top ring seats.

Unlucky #7
 

You are all knowing. Yes, my #7 piston has a crack in a ring land too. How is it possible that we both had the crack on #7? Does that cylinder have weird thermal characteristics that would cause this or just dumb luck that it happened on that one for me. Then again, there might be cracks on other pistons too. When I found that one, I stopped looking closely at the others figuring I need to now go to plan B, whatever that turns out to be.

Today is my birthday, so I can't say this is much of a present. Then again, I haven't accidently hurt myself on this teardown, so I guess I'll have to accept that as the consolation prize. :oogle:

OJ

You guys are scaring the crap out of me. I'm beginning to think that I need to completely tear my engine back down and go through everything again.
It's like Googling your medical symptoms!

Due to the design of the factory Q-jet Intake number 7 can tend to run lean.

It almost needs to be fitted with one step colder plug then what the rest of the cylinders can live with.

If your not looking to make over 420 or so hp this is a good reason to run the Performer Intake over a non ported stocker since it's hasa better flow balance across all its runners

Happy Birthday!

FWIW, if the bores are ok plan B can be replace the problem piston with a good one and still move forward with the rering plan. I don’t know for sure, I would have to look, but I would think I would have some STD stock 67 to 75 400 pistons squirrel’d away you could have for shipping cost. The later 71 and later low compression engines don’t usually have issues with ring lands, and may be better candidates for std replacement pistons.. I had a complete set I gave to someone that needed a set of rods. I think I have another STD set somewhere.

That's very kind of you. Thank you. For the time being I'm going to hold off and think this through. I had similar thoughts to your suggestion. I'm trying to remember what happened to the set of standard size pistons I had from my last engine. It's so long ago, I can't remember if I tossed them out or kept them.

I agree with Mike on plain iron rings. Moly rings require a much finer cylinder wall finish ( 15-20 RA) than iron rings do. The proper way to achieve this finish is to start with a 280 grit stone or dingleberry hone followed by a 400 grit stone /dingleberry hone then finished with a plateau brush. Assemble these cylinders with oil and you WILL induce cylinder glazing. Plain iron rings and a 280 grit hone will give you a cylinder that will seat fairly quickly, especially if you have noticeable taper in the cylinders. Come to think of it, all we had for aircraft recip engines were plain iron ( chrome cylinders) and chrome rings ( steel cylinders). We honed the cylinders to a 280 finish.