Rocker arm adjustments on 250 Chevy

[Rick Yeager]

I was wondering if anyone could tell me how to adjust the rocker arms on a 79 Chevy Pick Up 6 cylinder 250 CI engine. Two books give different ways. So far we have bent 6 push rods and the engine is still only running on about 2 to 3 cylinders at best. Any recommendations would be appreciated and could help me avert a close encounter of the worst kind with a straight jacket.

Thanks. This is a great forum.

Rick

[poorboy]

Rick:
How are you trying to adjust them?
Poorboy

[Rick Yeager]

Poor Boy,

I thank you for taking the time to reply.

The initiall problem was that there was only 20 pounds of compression in number #2 piston while the rest had 130. The manifold vacuum was 30 and fluctuating widely. When we took the rocker cover off on Thursday night, we found that the exhaust lifter on #2 was not pumping up and figured that was the cause of the problem. We put in new lifters, push rods and rockers. Mike adjusted the rockers while I cleaned the parts to put back on. Mike is a good mechanic, makes everthing look easy and does things three times as fast as I can. But the engine would not start. Later Mike figured that it had no compression--probably because the rockers were too tight. Mike worked on it again Firday and found the bent push rods. He put it back together and it would hardly run.

Tonight I took the valve cover back off and checked all the push rods for straightness and the lifters for mushiness. All checked out well. Then I readjusted the rocker arms using the old #1 piston up and then #6 up system. I think that it was right this time although I can not figure what I did diferrently than Mike did.

I checked and the rocker arms were both moving equally on #2 and the new lifters are firm but the compression is still 20-30. There was no blow by or backfiring or external signs of a head gasket leak originally. The only problem was that the truck just seemed to miss badly when it was cold but that cleared after it warmed up


Monday I will pull the head. Hopefully, it will be an easily fixed valve problem or an unusual head problem but I fear it will be a bad piston.

I guess you have already figured out that I am not putting this engine in a Cobra . Nor am I much of a mechanic. Again thank you for prompt reply and interest even though this is not a Cobra or even a Ford problem. I will let you know what I find.

Rick

[jeff_taylor]

Rick,
The fluctuating vacuum sounds like a burned intake valve, but a cracked piston could also be causing this problem on a 6 cylinder. Did you try the old "squirt oil in the cylinder and recheck compression" trick? This sometimes will reveal a piston crack. Is there excessive blowby (crankcase pressure)?
Why not a 6 cylinder cobra? Just mentioning that would cause much heartburn to the Chevy vs. Ford FE vs. 351 stroker vs. 460 debate!

[poorboy]

Jeff:
I know of a couple of 6 cyl. Cobras already. One has a Buick Grand National engine in it an another has a Tarus SHO, converted to rear wheel drive.
Poorboy

[Rick Yeager]

Jeff, before I pulled the head I tried your suggestion with the oil. It made no difference in the compression level.

Poorboy, we pulled the head off this evening. The cylinder walls are perfect. There is about a one-eight inch superficial triangular nich in the top of the piston just to the out side of the dish but it did not even get close to the outer edge of the piston. The valve looked good and there were no visible cracks or signs of a leak. Hopefully, I can get the head to the machine shop Wednesday to be magnifluxed.

If I do not get it fixed, I will put blue flame decals on it and try to sell it to the Bow Tie contengency of this club as an "original Corvette engine." If they would put a Chevy engine in a Cobra there is no telling what they might buy. Just kidding please do not fillet me with negative posts.

If you do not see the results of the magniflushing in this post in a few days then check the For Sale thread.

Rick

[Cal Metal]

Rick;

How does the book tell you to adjust them? I would assume they are hydraulic.

[Rick Yeager]

Cal, the way we read the book the first time was to tighten the rocker arm nuts to 19 ft/lb. They were hydraulic. As I mentioned before, this lead to disaster. It held all the valves open and bent 6 push rods. Finally, I tightened them the old way by tightening the rocker nut while rolling the push rods until they were no longer loose and then tightening 3/4 to 1 turn. That worked.

There is only a small nich on the piston and a more like a scrape on the exhaust valve. The valve appears to be seated OK. There are no visible cracks in the head or the piston and the rocker arms went up and down normally before I took them off. I have no good idea of the original cause. I think I will never know because I think I am going to junk this engine and get a rebuilt rather than putting more money into this one or maybe go to a 350 V8.

Rick

[Dominik]

I reread the replies two times, but can't figure if you checked the cam lobes.

if they are not opening the valve wide enough (worn) you won't get enough air/fuel into that chamber to get a good compression reading.

as for the engine discussion:
we have some very pooly powered Cobras in Germany.
Ford V6 2.6 or 2.8l (150 cui) and i have even seen one with a VW beetle engine in the rear.

but maybe that has been the starter for the tank engine in the front - maybe not!

dominik

[Rick Yeager]

Dominik,

I apologoze for being so slow to reply to your post. Thank you for your interest. I did not measure the lift of the lobes with calipers. But I did watch the rocker arms and feel them with my hand as I turned the engine over. Both intake and exhaust valves looked to move normally after the lifters were replaced and adjusted correctly. I have had a vetern mechanic who also taught automotive arts in high school, two expirienced mechanics and a retired jet mechanic look at the head, valve and piston. All say they have not seen anything quite like this. I have given up.

Financially a crate V8 engine will probably be the best choice. Our teenage boys think that this is a great idea, but I like the simplicity of the old 6 cylinder Chevy.

Let me know if any one in Gemmany might need this old 6 cylinder engine for their Cobra. I would be glad to send the pieces to them. I would even be more glad to give it to someone to put in a Cheetah

My great grandfather came from a small town not far from Stutgart. Several of his borthers and nephews followed him. The last German-born Yeager who I personally knew, was Wilhem Yeager. He died about 10 years ago. He used to work with us when we filled Uncle Frank's silo when I was a boy. He felt that he was the only one who could make the mud right to seal the doors. Some of Dad's family still comminicate with the Yeager's in Germany but I do not know them.

Rick

[Dominik]

hey rick,

so you are almost a german!

go for the V8 in your cobra. it's easier than playing a V8 CD on your car's stereo to simulate a V8 under the hood



best wishes,

dominik

[Rick Yeager]

I would like to thank you all for your suggestions and replies. The old truck is now back on the road and running well. Because of a busier than usual scheule it has taken a long time getting it back to the land of the living.

The problem turned out to be kind of unusual to me. The timing gear on the cam shaft had come loose and slipped forward. It had hit and rubbed the timing gear cover. Presumably, when it came forward the timing was changed enough to catch and damage the valve train of that one exhaust valve only. The lobe on the camshaft was also lightly gouged. Everything else was fine. We replaced the camshaft and cam gear as well as the timing chain while the front was off.

I talked with a friend who built four cylinder race engines. He said that he had seen this happen on the Pontiac four cylinder engines but not on a six cylinder Chevy.

Now, Dominick, Where can I find those V8 sounds for a cassette tape player?

Again thanks to all for your help.

Rick

[Dominik]