[1968GTO421]

I am putting this under members helping members even though it deals with engine issues. I bought my GTO locally from a couple from Utah. They wanted an iconic car but with a new baby sold the GTO for a new SUV with full infant safety equipment. Anyway I bought it in 2014 but had it stored until 2016 since we had found our dream home right after the GTO purchase, fixed dream home up and built a garage; then we had to fix up the old house to sell. Getting the GTO to its new home went well but I haven't been able to discover what exactly my GTO is. My spine went to h--- moving tons of stuff so now, I'm going to have to have spine surgery so the GTO fund will be depleted for a few years except for small stuff (brake pads, spark plugs, filters, etc).

The sellers had the great paint job done and upholstery so I am good there. They had a man in Coeur D'Alene Idaho rebuild the non-original engine for them. I found the engine number (9792068) behind right cylinder head and with the help of Ames tech guys learned the date and XF made it a '69 Grand Prix 428----all good. (GTO also has the '69 and up single piston disc brakes replacing the original 4 piston calipers.) Despite being a '69 engine, it has the 8 bolt timing cover/water pump, and 6X-4 heads. The intake is a Performer with an Eddy carb (w/cracked body=leaks). (I have a good Holley from another car to use.) Ignition is a very old looking Mallory Unilite.(I swapped some parts for a new MSD RTR.) Cam is unknown...a Ford friend said it had an "stock cam sound"?? The sellers had used the same oil in the GTO for oil changes as for their new cars --- 0W20 synthetic. The front and rear crank seals weep oil and at idle the Autogage oil gauge reads <20lbs. Never goes over 40 psi. (Gauge or engine problem?). Sellers had the water pump 'go out' and had a "classic car mechanic" replace it. (I recognized his name as a Tri-Five Chevy seller/buyer/mechanic.) The engine always runs hot (mechanical Autogage unit) around 230* or more, despite full radiator. I wonder if the water pump divider plate wasn't clearanced properly or left out entirely?

I have questions the sellers couldn't answer about the engine "rebuild" but they gave me the name and email of the man in Coeur D'Alene who did the work for them. I sent him several emails w/pic of the car and the PO's names, none bounced back, and he never replied. The questions I had for him were these:

"Is the GTO’s engine a 428 w/ stock bore/stroke?

If not, was a 455 rotating assembly put in it? (The sellers, to me, thought this was a possibility.)

Were new bearings and pistons/rings put in? Bore/hone?

Were new crankshaft end seals installed?

What camshaft is installed in the engine?

New lifters? Valve springs? Timing chain?

Any work done on the 6X-4 cylinder heads?
Valves ground? Heads shaved? Stock or ARP rocker studs? Any porting?

Chrome alternator appears to be one wire. What brand alternator? What is amperage output?

Is the TH400 trans the one that came on the 428 or the one that was original to the GTO? Has it ever been rebuilt?

The rear axle has a Suregrip tag on it (PHS says car originally no posi). Is it the original GTO axle or the one from the Grand Prix? What ratio?

At my age and health, I don’t want to dig into the engine or electricals if I don’t have to, so any info you give me will be greatly appreciated……Thank you."

I thought these were non-threatening questions and had hoped for some info from him but nada. I did include the sellers' names and pic of the car to help his memory. I've thought for some time to put out the builder's name and location in case a forum member knew him and could get the info for me; but did not know if this was a good thing to do or not. If this was 15 years ago, my body and pocketbook would allow me to just pull the engine and take it down to see what is what. But as previously mentioned, this isn't feasible for several years. I can crawl under to get info from the trans and rear axle but the engine insides are a dilemma.

Anyway, I throw this problem out to see what better minds than mine think should be done to ascertain engine rebuild status and what parts actually are in the 428. My thanks to all!

[ponyakr]

Sorry for all your problems.

My suggestion is that you contact area Pontiac clubs. There may be a nice Pontiac guy near you, who would be glad to come out and try to help you ID your engine.

But, it will take some precise measuring equipment to accurately measure your cam specs. Some things about the internals, can only be determined by opening the engine and taking a look, & measurements.

Wish I could tell you a better way to do it.

Good luck !

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http://www.tarheeltigers.org/

https://www.facebook.com/groups/101855759877277/

[tom s]

First thing do a oil change and put in 10-30 or 10-40 and see what the oil pressure is.Then check the timing.Pontiacs will run hot if retarded.Set it a 12 init with the vac unhooked and see how much total it has and where it comes in.Usually 34-36 total with iron heads is in the ball park.You might use dyno oil and see if it stops some of the leaks.Good luck with the project.Tom

[400 4spd.]

All good advise above. Absolutely change out that oil.
Realistically, I wouldn't expect the engine builder to know the answers to questions regarding the transmission or rear end. Getting some help from someone with Pontiac knowledge who can get under the car with good lighting and a wire brush or some scotch brite pads is your best bet for getting the facts.
The transmission might still have the metal tag riveted to it that has the 2 letter transmission code painted on it. With some research, that would tell you what it is from.
I can't speak for the 1969 GP, but it might be that they used the flat top axle tubes. My '72 has them. Instead of round axle tubes, see if the tops are flat on yours. The GTO did not use the same housing as a GP and will have round tubes.
There are also raised part numbers cast into the center section area that may be of help. Axle ratio (letter code) stampings are on the axle tubes.
Between the GTO and Grand Prix forum sections there is a huge knowledge base that can answer questions regarding casting numbers and stampings.
If you were closer I would be glad to look at it with you.

[1968GTO421]

APPRECIATE the info, all! I have ascertained that it definitely is a '69 428 from a '69 Grand Prix. Before I knew of the Forum, the Ames Tech guys helped me with pics I emailed them. So we know bout the "outside" of the engine. My concern, did the guy actually rebuild it or just toss in a used engine from a GP parts car. Since it has '69 disc brakes, I wondered if he put those on from the GP, and if he did that, could he have used the rest of the drive train from the GP?

The 8 bolt timing cover/water pump on a '69 engine seems to me he used the one from the GTO's 400 so pulleys and all would match. Since 6X4 heads are from the later '70's, I feel the engine was down to a short block at one time. Could it have been really rebuilt or just bottle brush honed with new rings and bearings and buttoned up with the new "odd" cam?

I guess saving $$$$ for a real rebuild in the future is the best idea and just enjoy the car in the interim, driving it easy so I don't throw a rod. (And checking timing and doing oil changes with dino oil.)

[John V.]

You posted a typo in the OP, your block casting is 9792968. As you already know, this was the '68 & '69 block casting used in all 428 engines for those 2 years (the '67 428 block casting was 9786135).

The XF engine manifest code was not used in '68, was an auto trans GP code in '69. Another clue that it was originally part of a '69 engine, the Engine Unit No. is likely 7 digit (1st character always a "0"). Very early '69 engines were stamped with a 6 digit EUN as had always been the practice, but just after the start of '69 production, PMD went to a 7 digit EUN (at year end, they fell short of 1,000,000 units, so 1st character remained a 0 all year).

Some '69 428s used 2 bolt mains, but the XF was supposed to be 4 bolt so hopefully that is what you have.

Local guy here builds nothing but Pontiac engines. He figures he's built hundreds. He says that sometimes guys will ask him what cam did you put in my engine, years after the fact? He shakes his head, how the heck can he remember that? That is why he gives the specs to the owner.

Likely that is what you ran up against.

If the guy you bought it from didn't keep receipts, a cam card, and other spec details, you are probably out of luck. The engine builder isn't likely to have any records.

I assume you asked the seller to provide any and all receipts for the engine build?

You should be able to identify the rear axle, much like you did the block. But any decode will assume the guts haven't been swapped. Get the casting p/n and the cast date code off the cast center housing and the manifest code stamp off the axle tube. The gear ratio can be determined externally to see if it matches the manifest code.

"Sure Grip"? Isn't that a Chrysler marketing name? Assuming it is a PMD rear, I assume you meant to say "Safe-T-Track", PMD's name for their Limited Slip Differential option.

Repeating what 400 4 spd. wrote, the trans will also have nos. on it. I'm not real familiar with how the TH-400 was marked but pretty sure there will be a manifest code designation and also a VIN stamp on it. Collect those nos. and you'll be able to ID the original origin of it. Again, no way to know if it has been modified internally.

Guys on the GP forum might know if the '69 GP TH-400 used the same tail housing as the GTO or a long tail like the big cars (I think that is correct to say). If the GP used the long version, that might be a clue as to which one you have.

I think you really have answered your own questions. Enjoy the GTO as is. Unless and until you do a rebuild, knowing what is in the engine won't do a lot for you. If you develop problems, you'll have to disassemble stuff and you'll be able to determine what you have then.

Meanwhile have fun with it!

[poncho-mike]

The 69-72 GPs were stretched A-bodies. The rear end housings were slightly different (there were flat spots on top of the axle tubes), but they would bolt directly into your GTO with no problems. If your rear end is a 2.92, 3.08, or 3.23 limited slip rear end, you should hope it is out of a 69 GP. The Grand Prix used 4-pinion posi units in the 3 series carriers. The same gear ratios in Lemans and GTO rear ends were 2-pinion units. That only applies to the three ratios I mentioned, the 3.36 and higher GTO rear end used 4 pinion limited slip rears.

The GP TH400 were also short shaft trannies, and bolt directly into a GTO with no problem. A TH400 out of a 69 GP with a 428 may even be a little beefier than the GTO unit since the GP was much heavier and had an engine with more torque.

The disc brakes out of a 69 Grand Prix will fit directly into a 68 GTO, assuming the GTO originally came with disc brakes. The brake lines and proportioning valves are different for disc and drum cars.

If you don't have the original receipts, you're probably out of luck. You can determine the stroke of the engine if you pull a head or the oil pan. If I wanted to know the stroke of an engine, I would try this: Run a small rod into the spark plug hole, find bottom dead center, mark it, then find top dead center and mark it. This assumes you can get a rod all the way to the bottom of the bore. Then find someone with a 400 engine and a 455 engine, and do the same. Now you have references that you can use for comparison to determine what your engine is

[1968GTO421]

Thanks for the tips on ascertaining my engine's size, we're pretty sure it's a 428 out of a '69 Grand Prix that may (or may not) have donated more parts than just the engine. Below are photos taken 2 years ago of the engine number behind the right cylinder head.

[tooski]

The number looks like '9792068'. From the chart I have, the closest is 9792968 which is a 1968 or 1969 428.

[1968GTO421]

Originally Posted by tooski

The number looks like '9792068'. From the chart I have, the closest is 9792968 which is a 1968 or 1969 428.

I sent the pics to Ames Tech guys (before I knew of the forum) and they looked and discussed and concluded (with you) it was 9792968, that the guy stamping engine numbers that day had a bad day.

Unlike several years ago, i looked more closely at those pics and decided that the engine was too dirty to have only 4-5K miles on it since the rebuild. I'm thinking that the 'rebuilder" just pulled out the "bad' 400 in the GTO and swapped in the running 428 from the donar Grand Prix. Does this make sense?

[LenCaverly]

If your concerned about the overall health of the engine do the basics ,compression test will tell you real quick if you have major ring seal or valve problems, Next change out the oil to 10/40 racing oil of your choosing ( racing oil because it has the required zddp to protect your camshaft. There are many things you can do to check individual components of an engine without tearing it down but first start with the basics.


Len C

[Ben M.]

If the rest of the engine looks like those pictures, there's no way that engine was "rebuilt" recently. You don't say when they had the engine done, but I've had engines that I've driven daily that I rebuilt that were cleaner than that after 5-6 years.

I wouldn't worry too much about what's in it for now, get the oil correct, check timing, and go from there. The water pump almost surely has the divider done wrong and o-rings either hardened or missing (new pumps don't come with them) so that job will probably need to be done too. If the oil pressure still sucks, there's explanations but as long as it isn't rattling or knocking you've probably got time to keep it mobile provided you don't abuse the engine.

[1968GTO421]

My Thanks to Ponyakr, Tom S, 400 4spd, John V, Poncho MIke, Tooski, Len Caverly, and Ben H for all your responses and generous help. I have some thoughts on some of what was said and will add it later when m wife is done with the computer. For now, I wanted you all to know I appreciate your thoughts and advice on my problems.

[John V.]

Originally Posted by 1968GTO421

I sent the pics to Ames Tech guys (before I knew of the forum) and they looked and discussed and concluded (with you) it was 9792968, that the guy stamping engine numbers that day had a bad day.

9792968 is an "as cast" no., it was not stamped. I think you are just misreading the no. and/or the photo image is deceptive. With the block out and the p/n cleaned up, I am certain there will be no confusing that 5th character, it will be a "9" that will look exactly like the other two "9"s in the p/n.

The Engine Unit No. and Engine Manifest Code stamped on the front of the block by the Engine Assembly Plant in Pontiac, Mich or the partial VIN stamped on the front of the block at the Final Assembly Plant sometimes did get messed up.

But it would be almost impossible for the "as cast" p/n on the ledge behind the no. 8 cylinder at the rear of the block to get screwed up since the problem would have occurred in the mold at the foundry when the block was poured.

Just thought you might like to know.

[1968GTO421]

Originally Posted by John V.

9792968 is an "as cast" no., it was not stamped. I think you are just misreading the no. and/or the photo image is deceptive. With the block out and the p/n cleaned up, I am certain there will be no confusing that 5th character, it will be a "9" that will look exactly like the other two "9"s in the p/n.

The Engine Unit No. and Engine Manifest Code stamped on the front of the block by the Engine Assembly Plant in Pontiac, Mich or the partial VIN stamped on the front of the block at the Final Assembly Plant sometimes did get messed up.

But it would be almost impossible for the "as cast" p/n on the ledge behind the no. 8 cylinder at the rear of the block to get screwed up since the problem would have occurred in the mold at the foundry when the block was poured.

Just thought you might like to know.

John, I concur, a good cleaning at a machine shop should "expose" those numbers clearly and, yes,its obvious they are cast in the block as is the "transfer lug" adjacent to them.

One friend suggested that the engine may have internal dirt and that dirt might be caught between the oil pump check ball and seat causing low oil pressure at idle speeds. He suggested high detergent oil frequently changed.