Engine Problem 327/365HP; Timing Chain ?

[Mikey1]

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....maybe 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

 

[Tempus_Fugit]

bent pushrod on the one with the weird angle? Remove the pushrod and roll it on something flat to check for straightness.

 

[Hib Halverson]

Well...if you hear poping from the exhaust, you know it's not a cam problem as you wouldn't hear that if the valves were not opening.

You said you changed the cap and wires and that you had spark and, I assume, that means you checked each plug wire for an arc from the plug connector to ground as you cranked the motor.

But...did you pull the spark plugs and inspect them? I'd check the plugs carefully.

If the timing chain has jumped a tooth, the engine would run really, really bad on all cylinders, not juse 2 and 3.

Did you check for any bent pushrods?

 

[3TT3V]

perhaps you just have 2 spark plugs which fail at high RPM (load).....try switching wet plugs #2 and #3 with 2 other plugs. Run the engine to operating temperature, rev high a couple times, shut off, allow to cool, and now check all 4 plugs aforementioned. Good luck.

 

[69autoXr]

I agree with checking for bent pushrods, I would also check for splitting of the rocker arm ball seats.

Did you check the timing? I've had distributors turn after high-rpm runs.

 

[BLACK MOON]

I had the same problem and it was the rocker arm studs 'pulling' out of the head. Look at the top of the studs from the side and see if there are some that are taller than the others. I repaired one then the second and third did the same thing within days. Don't freak like I did. They make a kit that requires drilling the casting around the stud and inserting a pin. You'll also need a new 'straight' push rod. Some times it will also gaul up the seat in the rocker. I chose to tap mine and use threaded studs but they need to be the ones without a shoulder. Finally I said screw it and I'm putting on a new set of Edelbrock RPM heads. I hope that isn't yourproblem but if it is it can be fixed.

Let me know if that was the problem because it sure sounds like it.

 

[Sixtyfourvette]

I would check your carb, the holleys are bad about picking up trash in the needle and seat, which will make it run very rich. Sometimes also, the power valve will develop a leak leading to the same problems. I would also suggest a little hotter plug, as the 43's are a bit cold for most everything but high rpms, as they tend to want to foul at lower engine speeds and especially if the carb is dumping too much fuel in there. We used to run 43's while racing but would change to 45's for the street. jmho

Larry

 

[Mikey1]

Thanks guys....

...I will check for bent pushrods probably today or tomorrow. Also will change plugs and check timing...dist seemed to be mounted tight...but I haven't check if it could have moved...and you are right....if you haven't gone through all standard check procedures...you'll never know.

Will check the Holley as well....however I have not had ANY problems with it so far....

Timing chain has then stepped back as the possible source...

....I'll keep you updated.

 

[Jack]

I'd check all those things mentioned ... but I'd also reconsider timing chain ... if it's real bad it may've let cam timing get out of whack so much that a valve hit piston ... a bent exhaust valve can cause popping in exhaust.
JACK:gap

 

[redc4corvette]

Just through a timing light at it and see if the timing mark moves up or down at idle?
with the dist vacuum disconected if it moves up or down to much may be a timing chain? That motor loves to bend push rods and score rocker balls.
If it were me I would do a compression test with a gauge.see if the cylenders are with in 10% or each other.Just my 02 worth.

 

[Mikey1]

We did some checks again today...looked for bent pushrods...but seemlingy they are all ok. Chnaged spark plugs now to the hotter R45. See how they cope with the engine.

Well....and for sure did the timing light check....I couldn't believe my eyes.... .....16 degrees instead of 10 !

...everything was mounted tight....but I have heard that under hard acceleration timing could change....

...well in this case it added some 6 degrees.....when removed the engine was running absolutely fine.

Isn't that great ?

But I never ever have seen that before....

 

[Jack]

Another thing to consider: a flat tappet cam (solid or hydraulic) will walk front-to-back under hard on-off throttle and the ignition timing will change. I'm not talking just retro-fit roller cam ... they'll all do it ... especially if the timing chain has some wear (and it don't take much). You can cure the walk with install of $6 cam button between the nose of cam/cam gear and inside face of timing cover. There's also a trick spacer setup that replaces the freeze plug on rear of cam bore. I run a cam button on flat tappet circle track car ... have to. Correction, the later factory OE roller cam motors have a retainer plate that prevents cam walk.
JACK:gap

 

[iron cross]

A common problen is to substitute a R43 for the non existant 44`s. The first thing to do is to change the plugs from AC43`s to AC45`s. The 43`s are too cold for street driving and prone to fuel foul. It will probably suprise you how much cleaner it will run.

 

[Vetsvette2002]

Michael,

Check your timing again, this time a little differently. With the timing light hooked up blip the throttle a few times and allow to re-settle. Did it change? or stay the same. If it changed, I would look at the timing gears/chain. It won't have jumped a tooth, as Hib said, the whole engine would run bad. But, the gears was plastic coated and after 25-40 years, the plastic coating is gone allowing the cam gear to change its timing, it will advance and retard as it wants. GM put the plastic on the gears to reduce noise. If this is the case, replace the gears and chain - only repair for this.

If the timing is not changed, Then go after the plugs and plug wires. Are you absolutely certain you have the plug wires on the correct plugs? More than one master mechanic has missed this. Also check the cap and rotor for internal arcing.

Don

 

[Mikey1]

No....everything seems to be fine now. Just did the timing adjustment....

...but thanks for the additional hints...

Michael

 

[pvtpilot]

Glad to hear the old "365" is feeling better. Most of the likely (and some not so likely) causes have been identified above. However, one thing that puzzles me is initial timing of 16 degrees is a little beyond factory recommendations, but would not cause cylinders 2 and 3 to miss. Secondly, you said the idle dropped to around 600.. typically an advance in timing will cause the idle to increase.. In any case, timing varying 6 degrees one way or the other will not cause only two cylinders to miss.. The first thing I would do after a simple wiring check would be to replace the plugs. And, as has been recommended here, for normal driving use a little hotter plug.
Best, Glenn

 

[Mikey1]

Done....

...now Delco R45, new cables, new dist cap.