I was driving through some country roads some days ago and was quite pushing and revving the engine. After w a while...driving back....I had some problems which I assumed to be partial ignition failures...

it looked to me as 2 cylinders were not working properly....and I heard a popping noise of fuel exploding in the exhaust....

...also idle dropped down from 800 to somewhat below 600 and the engine would die if I would step on the pedal....however it was revving up more or less correctly with no starving beyond 4000 easily (I stopped it there in order to not break anything...).

I changed ignition cables to a complete new set, dist cap is new as well...underneath is a breakerless ignition...and there is a spark on every plug which I tested as well.

However...sparkplugs of cylinders 2 and 3 have been wet of fuel....

....all the others have a light brown color....I use Delco R43 plugs.

After all that checking had been performed I feared something like a dead camshaft....or even worse and went for compression testing.

Result down below:


For my eyes this looks ok with no dramatic differences whatsoever. That means to me, that valvetrain and possibly piston rings are ok.

Today I went to check valve play which turned out to something between 0.02" and 0,035" with a cold engine (AIM says should be 0.03" hot. Is there any value that one could use for a cold setup ?).

This is how my valvetrain looks.....all springs seems to be ok.





Only thing that I found interesting is that the one rocker arm on the outlet valve of cylinder #4 is slightly more out of angle than the others.



With my Digitalcalipers I tried to measure the valve lift....but that was a bit difficult...only telling that they're all something around 0,377" ....with to many sources of false measurement. However this tells that the camshaft seems to be ok....at least no major damage.

Well....my current consideration is that something has to be wrong with the timing chain....mybe it is lengthened and revving the engine quite hard made it jump by just one tooth....

...any thoughts ? I would appreciate your comments.

THX Michael

 

From your description, it does not sound like a timing chain problem. You would have problems in all of the cylinders if that were the case. I would take the valve springs out of the two cylinders and see if you have broken or weak springs. Many times these problems are not obvious until you completely remove the springs. You can remove them without taking the heads off by using a bent screwdriver through the spark plug hole to keep the valve from falling out or use compressed air to put pressure in the cylinder. Another question: Have you put new valve seats in the heads? Usually they are pressed in and maybe a couple came loose. Good luck.

 

Power valve on the Holley? I went through that recently.

 

Quick way to check if the timing chain has skipped a tooth is to check the ignition timing. If still dead on, then timing chain is still in the correct spot.

As for checking the valves, agree that could be broke without seeing it, until removed, but that is rare. Compressed air, or even a rope fed through the spark plug hole (and then piston brought up to TDC) to keep the valves in place while removing them.

You did not mention any valve train noise, so I would normally discount bent pushrods - but that is always a possibility with your rocker looking askew. When checking the valve springs, check the pushrods for straightness, and the rockers for wear and galling, etc.

Note that 43's are pretty cold plugs for most Chevy engines. Unless your's is very highly modified, I would step up to either 44's or 45's. But also understand that you probably run on the Autobonn, and don't want to melt any pistons! So maybe the 43's are just what you need. Most of your symptoms relate directly to fouled plugs (loss of RPM and power, popping in the exhaust, etc.). Now it is not normal for plugs to foul when being run semi-hard to hard. Fouling normally occurs when driving around town in a lot of stop & go traffic, so doubt that all of this is just fouled plugs.

Hope you find your probelm quickly, and with minimum cost!

Plasticman

 

Did you replace the plugs also? 43's are a cold plug and, though they are great for high rpm use, they are more likely to load up under low rpm conditions than a warmer plug. Perhaps your problem didn't result from the spirited driving but from the easy driving that followed? Fuel mixtures are often uneven between cylinders on carburerated engines and it's not unusual for some plugs to foul and not others.

 

Thanks guys.....

....will check for a bent pushrod today...also will pickup some new spark plugs...they haven't been an issue so far. However I do drive mainly in cruise speeds and rev up the engine occasionally. Having a 3.08 rearend numbers are calm....and even with some 110 to 120 on the clock revvs do not go largely above 4300 rpm....with still plenty of options left..

....this is just the lifeline of the tires.

Before that all happened I had a longer weekend trip for about 600 miles without any problem....with almost 100% top down....and mainly between 70-80 mph.

 

This is an easy problem to fix. Put in hotter plugs.

 

...so did some checks today....no bent pushrods.

Just the timing had changed to some 16 degrees.... ....never seen that before....

...also put in Delco R45's and now everything works fine again....unbelivable.

Yes someone told me that under hard acceleration this could happen....but with every singel screw sitting tight...you normally don't believe that. Thanks for your help !

 

You say the timing changed 16, when you reset it was the hold down loose??

 

No...defintely not...rock solid wrenched down...

 

Beezaaaare!!!!!!!!!!!!!!! Oh well only fix it again if it breaks. You will be better with the R45 firing those cylindars. I've got the 365hp with 45's set at initial 16 degree's and she is a happy beast.