[NorthStar67]

Hi all, new to the forum, not new to Pontiacs. I had an experience a while back with an engine that break or bend the same pushrod, twice. The engine would warm up to operating temperature just fine, then bang. Finally it hung the valve open and crashed the piston and valve. Turned out to be a small crack running through that valve guide. It would warm up, pinch the valve, game over. Just a possibility. Good luck with it.

[steve25]

North Star I can see that happening if the the head your taking about had been fitted with a 1/2” OD cast iron replacement guide, but we need more details on these casting 62 heads on his motor.

For one thing Pontiacs have there guides just drilled into the cast iron of the head, and these days unless the guides are incredibly worn a ,030” non cast iron guide liner in installed and the n reamed or better yet honed to size.
This type of guide would have a hard time pinching a valve it would seem!

In terms of the motor you have posted about pinching a exh valve, what type was it, and was it a iron head ?

[NorthStar67]

steve25, the motor in my case was a warmed up inline 6 Chevy, based on a brand new service replacement long block. We just did some minor bowl work and did nothing with the guides, so I’m sure they were just drilled into the iron. So, yes, it would be good to know the history of those 62 castings.

[steve25]

In terms of jetting you are dealing with heads that flow 10% more then what the 389 heads did, your displacement has gone up by 4% and your running a much bigger Cam.

All these factors consider I would want my jetting to be on the safe side and start off with 70s in the center Carb and 72 jets on the end carbs.
This is up from a stock 62 on the center and 68 on the end carbs.

[geeteeohguy]

What these guys said about it being mechanical vs a lean mixture. I pulled the tripower off of a 428 engine in 1987 and bolted it on a 389 without even opening the carbs up and it runs fine to this day. Yes, jetting and calibration is important, and can lead to issues if out of range, but it is not your issue here.

[PontiacJim1959]

I am onboard with "no oil" seen in the valley area. With conventional oil, you should readily see this in the pockets in the valley. So I would check oil level, then pull the distributor and use a drill motor and pre-oiler shaft and prime the engine and watch for oil to appear.

Pontiac engines need the correct valve guide-to-valve stem clearances - they are designed to provide oiling to the valve stems. If they were made too tight, it could cause the valve to stick once expansion takes place when hot.


Lean condition? BS in my book. An extremely retarded timing at the distributor can cause a lot of heat in the engine to the point of making the exhaust glow, but your engine temps will also go high and you'll know its cookin' hot as when it cools down, you'll here creaking/popping of the cast iron exhaust manifolds as they cool - trust me on this one.

[1965gp]

Great catch on the oiling. I didn’t even think about that. Now that picture was taken after it sat over night but I would still expect there would be some oil?

I thought the lean condition was a reach. Possible yes; probable no...

[dataway]

Many years ago when I put a new cam and lifters in my high mileage 400 (YS), when I pushed it real hard it would often bend those exact two pushrods. Being a kid I just carried a couple of spares and would toss in two new ones on the side of the road. Almost always in my case you could just flop the rocker out of the way and pull them out. I actually put the T handle valve cover bolts on so I could get the cover off quick and easy Have no idea what the problem was.

[steve25]

Sounds like the story with your YS 400 was the new Cams valve lift combined with the stock amount of retainer to guide clearance , factory production machining tolerances adding up to be not in your favor and in heavy throttle , added heat followed by expansion of parts with the end result of collision, with maybe some valve float thrown in the mix just for more fun, lol!

[steve25]

To the OP here, I am not saying that your condition your dealing with was brought about by lean part throttle jetting by any means, but once you get it back up and running again your full throttle jetting will without question need to richer then stock dispite what others have said in there postings to you here.

certainly it will not hurt any to start off on the rich side and then back down as needed.

[ta man]

Where did the pushrods come from? I can see that they are used..I agree with most here..wrong pushrod length or valve spring bind. I'd like to see a picture of the rockers and valve springs.

[torqhead]

Originally Posted by 1965gp

Great catch on the oiling. I didn’t even think about that. Now that picture was taken after it sat over night but I would still expect there would be some oil?

I thought the lean condition was a reach. Possible yes; probable no...

Focus on the oil problem, there should be lots of oil all over that valley, all the other stuff that's being thrown out here about possible issues is a waste of time. If you don't have oil going to the top end of the motor, the downstream effect is heat and frankly surprised you only bent two pushrods.

Bottom line, focus on the oil.

[Skip Fix]

FWIW my high school hot rod street racer and class racer 409 Impala used to break rocker arms intermittently. Machine shop was supposed to check valve springs/retainers for clearance for the big solid cam. Fast forward 20 years ago when I got my own valve spring tester. Probably coil binding! If you can always double check every shop if you can. Also learned another potential cause on the 348-409 board with their weird chamber in the block the exhaust valve gets real close at .550 lift-my cam had. .590 - lash. Why the new motor I built recently has a notched block!

I also bent a 11/32 Melling RAIV pushrod just turning over my motor by hand checking clerances when the roller rocker got in just a slight bind was hitting the hex on the stud. So it does not take much to tweak a pushrod.

[Kenth]

No reason to worry about using an original 1965 Tripower on a 400 engine running lean.
I have used an to my GTO the original 1966 Tripower on my current 1969 RAIII engine for about 25 years w/o issues.
By nature of the beast a larger engine pulls adequate amounts of A/F due to the stronger signal (pressure differential) thru the venturies.

F.e. Pontiac used the same #7029268 carb (with same jetting) in 1969 for 350 H.O.-400 H.O. and 428 H.O. A/T.
Also in 1970 all A/T RamAir III, RamAir IV and 455 RamAir used the same #7040270 carb (and jetting).

BTW, for your issues it seems like coil bind.

FWIW

[steve25]

So Kenth, so when in your world does there come a need for jetting changes?

In mine, to make the best average Torque and HP numbers on a number of dyno pulls when just switching to different octane level and different blend type fuels we had to change the jetting to achieve our goals.

[Ceopro]

Originally Posted by 1965gp

I had a 400 built by a highly recommended local builder for my 66 GTO.

It’s a 77 TA 6.6 block with #62 heads. Summit 2802 cam. ‘65 Tri Power set up rebuilt by another local well known builder. Nothing fancy, just fun and reliable. Enough to turn the tires over and look cool.

I was driving at about 2000 rpm and heard a bang and then a few knocks, then it felt like it was missing. This is about 300 miles on the motor. When we pulled the valve cover an intake and exhaust rocker were off to the side and the push rods were laying in the valley area.

I have used this shop for years and are close friends with them. This guy builds all of their motors and they said he has only had one issue and he took care of it right away. The engine builder has been very active in trying to get it resolved.

We put new push rods in it and the shop is saying that it runs great until it warms up. Once it gets hot it starts to get a rougher idle and they feel like the exhaust valves are sticking which could definitely break a push rod.

The engine builder pointed out that while it is an original Tri Power jetted for a 389, it’s now a bored out 400 with an aggressive cam and it isn’t getting enough fuel making it run lean. Running lean the exhaust is supposedly getting hot and causing the valves to stick.

Now, I am not an engine builder by any means, but I have 400’s and 455’s that run on quadrajets all day with the small primaries. Is that more fuel than a center Tri Power carb?

They said the exhaust was getting up to around 600 deg, but the engine never seemed to run hot so is that possible?

I don’t want to cause problems but I also dont want to get stuck with a car I’m scared to drive.

Thoughts?

Have you put on a higher volume fuel pump? I had to put on a Carter 110 gph pump with the same 4 to 6 psi. This was after a 389 rebuild to a 400 with a slightly more aggressive cam and after having all the carburetors rebuilt. This corrected the lean problem and it ran great until the engine got hot. Also, had a cooling problem that I had to eventually take care of with a flowkooler water pump and alum radiator with tow electric fans. The final thing was to get the water out of the ethanol gas. Even after using lucas additives to the gas for octane boost and water removal, when I added heet dry gas (must leave in overnight), it made the difference in how it ran at high rpms. Also, check to make sure that the fuel line rubber hose right off your fuel sender by your gas tank is new and the right size. I found that mine was old and needed replaced. This also helped getting the fuel flowing properly. Hope this helps.

[Kenth]

Originally Posted by steve25

So Kenth, so when in your world does there come a need for jetting changes?

In mine, to make the best average Torque and HP numbers on a number of dyno pulls when just switching to different octane level and different blend type fuels we had to change the jetting to achieve our goals.

You just answered your own question.

It´s or never was like anyone buying a new car in the 60´s-70´s or using an original used street car nowadays checking for best average Torque and HP numbers every time they went out for a ride.
For most of these folks they were happy if their ride started and drove well.
And they did thanks to the people building them.

[steve25]

Ok folks the word has come down from on high, Kenth as spoken !

It’s a new day in the automotive world and in our hobby!!

It’s one carb fits all now,!

So Holley you look here!, do away with all of those different part numbers for Carbs that are within 50 cfm of each other and all of you other folks spending hours and a tank full of gas on getting your fuel injection map just right, just screw it, shut up and live with the out of box results, or that original program that came in your car’s computer before that cam and exh system change you made!

[Dynoking]

Valve guide clearance too tight. Valve guides not concentric with valve seats.

[Kenth]

Originally Posted by steve25

Ok folks the word has come down from on high, Kenth as spoken !

It’s a new day in the automotive world and in our hobby!!

It’s one carb fits all now,!

So Holley you look here!, do away with all of those different part numbers for Carbs that are within 50 cfm of each other and all of you other folks spending hours and a tank full of gas on getting your fuel injection map just right, just screw it, shut up and live with the out of box results, or that original program that came in your car’s computer before that cam and exh system change you made!

You seem resistant to simple facts.
Do you really believe Pontiac would mount wrong non-functional carbs on their vehicles?