Okay, first a bit of background that may be helpfull. i just replaced the heads, intake, timing chain and carb on my 289 in a 1968 mustang with auto trans. I put everything back together and ran a compression check (cold) psi was at130 to 150 on all cyllinders. I started the engine and it ran well but idled very fast around 2k. then I noticed no 3 was missing sochecked for spark and had good spark soI did a comp test on it and it was at 50 psi.so I checked the cylinder next to it and it was also registering 50 psi. Then I let the engine sit and it started up on all 8. next day I run a comp check on all cyllinders again and al are at around 30 psi. and the engine will not start. I have been playing with it for days and I cannot make any improvment sometimes it will start and sometimes it wont. when it does it runs fine (two hours last night). but today it will not start at all. does anybody know what is going on? can anyone help me? any input would be appriciated. thanks.
Kip

 

Did you retorque the heads? the intake? (Youre supposed to) As for your compression readings... well theyre all over the place. Are you usingthe testercorrectly? Youre supposed to let the needle bounce 5 times. Also, when you did your original compression test was there oil in the cylinders? That can raise compression readings.

Id say retorque the heads and intake (couldnt hurt to check the carb to), then try to fire it. Other wise it sounds like theres something seriously amiss with youre cam/crank timing, the chain perhaps?
-P.

 

When you changed the timing chain did you mark the position or did you reset the marks up on the cam and crank? If you didn't mark it then you may have tore-index the cam using a degree wheel.

 

Are your valves adjusted correctly?

This is the only issue that kind of explains the sudden and extreme compression loss that you have experienced.

It does not make total sense because I am at a loss as to why the compression was ok and then very very bad, unless you adjusted the valves after your first compression check.

Did your new heads come with guide plates for the pushrods? Did you change your rocker arms? If not, and your heads don't have guide plates, the stock rockers probably will have twisted to one side or the other causing your valves not to open.

This might explain why the compression was ok at first, and then decayed once the rockers twisted.

 

A little OT, but I want to say congrats LCC for car of the year!

I think you deserve it, killer car!

 

What's your oil pressure? And how did you adjust your valvetrain? And is it stud or pedestal mount?

 

ok, sorry for not responding. my internet crapped out after i posted. yes i think i did instal the timing chain correctly. i did not deegree the cam but I did alighn the marks. also at tdc no 6 is exactly on valve overlap so i think it is correct. my heads are stock original castings. i believe they are stud and the rockers azre original. i adjusted the valves several tim es using several methods. all of which do not help. i also did a compression test with some oil in the combustion chamber and it helped a bit. on one the compression went from 12 psi to 62 psi. and on the other it went from 50 psi to 100 psi. does this mean my rings are bad? why would this happen all of a sudden on in all cylinders?

 

and oil presure is good. oil is coming from the rockers and pressure is registuring on guage. also I used the tdc and ajust valvesx to 0 lash then tighten 1/2 turn method. also the intake almost closed and adjust exhaust. exhuast starts to open adjust intake method then turn 1/2 turn.

 

If you had re-ringed the engine and not had enough ring gap it might be possible togall all of the pistons and rings the first time it got hot..... but you didn't re-ring...

IDK, seems like a mystery to me....

I guess I would have to start pulling it apart and looking at stuff. I would probably leave it in the car for as long as possible though.

 

How many miles are on the rings? If the heads were rebuilt and put on with high mileage rings, there's the possibility that increasing sealing on the top end, overloaded the rings. If they were already worn to begin with, the extra force from better compression is put on them, and they could fail for any number of reasons. The ring lands were worn and when the top end was leaking, not enough for the rings to unseat, seal the top end and then the rings are overloaded and unseat from the lands. They could have just been old and the extra force caused them to crack etc.

If the heads were not rebuilt, then I'd suspect that they may be warped, and depending on the gasket you used, could be leaking.

It sounds more like rings though, the compression was good on all of them, it ran, then the compression was bad on all of them, plus oil in the clyinder makes the compression better.