Engine issue

[Jeff G 78]

I'm not necessarily asking for help here, but rather, I'm curious if the armchair Z experts can figure out what is wrong with my race engine.  Here is the background...

 

My engine is a F54 block with a shaved P79 head, Web Racing camshaft and a 3-2-1 header.  I run SU carbs and a ZX distributor with the E12-80 module.  I built the engine a few years ago and it now has two endurance races on it with a total of about 20 race hours.  Last weekend we raced the car and the engine was running great with plenty of power.  About 6 hours into a 9 hour race it started missing at high RPM just before a fuel stop.  We thought it might be a fuel starvation issue, though the AFR never went lean.  After the fuel stop, it began to run worse and worse, missing at lower RPM and losing power.  The driver radioed in and said that it died and he was coasting into the pits.  Oil pressure, water temp, and AFR were all right were they should have been while it was losing power.  All of the fuel was bought together and the issues started close to 2 hours into a fuel run, so bad fuel can be ruled out.

 

We began to try different diagnostics, but nothing seemed wrong at first.  It had fuel and spark, but wouldn't fire.  We thought maybe it had vapor locked, but even after it cooled, it still wouldn't fire.  Starter fluid didn't work, so I pulled the plugs and valve cover.  The plugs had a perfect light tan color and all of the valves were going up and down with no obvious problems.  Next, we checked the ignition timing and valve timing.  Both appeared to be correct.  With the crank damper mark at #1 TDC, the #1 piston was confirmed to be at TDC and the #1 cam lobes were both up.  The distributor rotor was pointing towards #1.  I then looked at the cam gear pin with the crank showing TDC and the pin was up where it should be by the naked eye.

 

Next up, the compression was checked.  This is where the first problem was found.  All 6 cylinders were near 140 PSI with all plugs out and the throttle open.  The compression should have been closer to 180 with my engine setup.  Again, the engine ran strong earlier in the race. 140 PSI isn't great, but the engine should run reasonably well with 140 PSI if that is the only issue.

 

Next, we tried a different known good coil as well as a known good distributor and module, cap, rotor, and plug wires.  We still got no fire.  The engine never even tried to start after it initially died on track.  Spark was checked at the coil as well as at the plugs and it showed good no matter what ignition parts were used.  The fuel lines were removed at the carbs and the electric pump fed plenty of fuel into a pop bottle.  We tried bump starting, starter fluid and new ignition parts with no luck.

 

My thinking is that somehow it must be valve timing or valve related due to the low compression readings.  It doesn't appear to have skipped timing and the valves appear to go up an down smoothly.  The distributor rotor turns as it should and oil pressure was always good, so the crank worm gear and oil pump/distributor shaft do not appear to be stripped.  The engine oil and water look fine with no signs of mixed fluids.

 

It could have bent valves, though all six have equal compression and 140 isn't horrible.  The engine does appear to puff a bit strangely when cranked, so it feeds the theory of valve timing or bent valves causing the intake charge to escape through the exhaust ports.

 

We also tried to turn the distributor back and forth while cranking.  It never sputtered, backfired, or coughed.

 

The engine never made any bad noises while running or when turned over via starter or by hand with a breaker bar and socket on the crank bolt.  The engine should not have been money-shifted, but with three drivers, anything is possible.  There was only one downshift per lap from 4th to 3rd gear.

 

So... I have not yet done any further diagnostics since getting home, but I will do a leak down and put a borescope in the plug holes within the next week.  If I don't see anything, I will pull the engine over the winter and tear it down to check everything.

 

Any theories?  Winner gets nothing other than bragging rights and internet accolades.

 

GO!

[siteunseen]

1st!

 

Valve springs

[240260280z]

timing chain stretch or guides coming loose/worn or tensioner not pushing far enough.

 

 

check valve timing marks again at tdc.

[beermanpete]

Is it possible the ignition pickup or reluctor have moved such that the timing is off far enough that it won't even pop? I suppose it would have to be later rather early for that to happen. Check the internals in the disturobutor. My father had trouble with his Alfa Romeo where the timig kept shifting, although the car still ran but poorly. We traced it down to a staked shaft coupling in the distributor that came loose.

Edited September 4, 2015 by beermanpete

[bartsscooterservice]

Did you use a spark tester ? Spark outside the engine even blue doesn't mean anything I have found out.. Also be sure the timing is correct ?

 

It could be in the head like siteunseen is saying. Worst case you have to dismantle the entire engine..

Edited September 4, 2015 by bartsscooterservice

[Jeff G 78]

I am not ruling anything in or out, but to clarify, here is what I do know:

 

Cliff, the valve springs are all intact and appear good.  They are high performance Schneider springs.

 

Phillip,  I am with you.  I think that the issue is very possibly in the chain guides or tensioner.  The top end of the guides looks fine, but until I pull the front cover, I will not know for sure.

 

Pete, I thought that too, but I swapped the entire distributor, so I'm leaning away from that being the issue.  I checked the rotation and the lash in the rotor at several positions and all felt correct.

 

Bart, interestingly, I did try to use a timing light to watch for ignition while cranking the engine and it did not work.  I will revisit this with another timing light since my advance light gets flaky at times.  I have never tried to use a light without the engine running, so I wasn't sure if not getting a light flash meant anything.  Again, I swapped the coil, distributor, cap/rotor and wires individually and all together with no change.

 

These are all GREAT suggestions and I would have said exactly the same things if it were me being asked.  Keep the ideas coming.  I'd love to figure out what happened without needing to tear it all down, but it will likely come to that.

 

I promise I will update the thread as I learn more, though I will not be pulling the engine apart for several months if that's what it comes to.  I'm moving the car in November to a new winter home where I have lots of space to work on it over winter.  

 

What does everybody think about the low compression and slight puffing?  I have run engines (not L Series) a tooth off and they still run fine, just down on power.  I would think that if it was off by more that a tooth or two, I would be dangerously close to having piston to valve contact.

 

Oh, one more item that I forgot to mention.  While diagnosing, we found that the crank damper bolt was loose by several turns.  The engine has 20 race hours on it and the everything was torque checked before this race, so would anything specific cause the bolt to get *impacted* and lose tension?  It could have happened when it jumped timing I guess (if the timing jumped).

[Captain Obvious]

You checked fuel delivery to the carbs, but did you verify that fuel is actually making it into the bowls? Maybe your little screens or your float needles have plugged up?

 

I know it's unlikely that both carbs did the same thing at the same time and I also know you said that it wouldn't start even on starter fluid, but I just want to play too.  

[beermanpete]

What about a problem with the Woodruff key that keys the distributor/oil pump drive gear? Perhaps, when the damper bolt loosened it allowed the gear to vibrate and wear or fracture the key?

[Jeff G 78]

Pete, that was my #1 theory and it still could be true.  I backed-off when I checked the distributor timing and found it to be where it belongs.  I will certainly double check it though.

 

Captain, it is certainly possible, though unlikely that both carbs clogged.  The fuel flow to the carbs was great.  I figured that the starter fluid would rule out a fuel problem, but again, I will revisit everything.

 

Keep the ideas coming.  Just because I checked stuff at the track, doesn't mean I won't check again.  At this point, I think it's a fun exercise for those of us who have been doing this forever to diagnose the problem.  I expected each of you to chime in quickly and there are a few others on the forum that I know will join the fun.  

 

It's a frustrating problem, but one that I WILL find the answer to once I fully inspect everything.  Hopefully, it's not a catastrophic problem and I only have to replace a woodruff  key or a faulty tensioner.  Fingers crossed...

[Mark Maras]

 I love a good mystery.

 How long did it take to go from the first symptom to dying? Was a compression check done prior to the failure? What is the source of the strange puffing sound when cranking the engine? I'm looking for another piece to the puzzle.

[Jeff G 78]

Mark, the initial high RPM misfire was about 5 hours into the race just before a fuel stop.  The car progressively got worse (missing at lower and lower RPM) until it finally quit running just after the 6 hour mark.  The last 15 minutes were far worse.  Prior to that, it still did OK, just had a misfire according to the driver.  I was in the car earlier and it ran fine, so I have no direct knowledge of the symptoms.

 

The driver kept reporting that water temp, oil pressure, amps and AFR were normal throughout.  We thought it might be vapor lock, so that is why we left him out.  In the past, when that happened the symptoms were similar, but there wasn't a quick fix.  This time, it was clearly something else since we let it completely cool and it still wouldn't run.

 

The compression check was only done after we checked the easy stuff like fuel, spark, and valvetrain.

 

The puffing was subtle.  It almost could have been confused as attempted firing, but it just sounded like the intake charge was being partially expelled.  Very tough to call since we were right next to an active race track with lots of background noise.

[Zed Head]

 

Oh, one more item that I forgot to mention.  While diagnosing, we found that the crank damper bolt was loose by several turns.  The engine has 20 race hours on it and the everything was torque checked before this race, so would anything specific cause the bolt to get *impacted* and lose tension?  It could have happened when it jumped timing I guess (if the timing jumped).

 

Is the damper itself still in good shape?  Still damping?  Maybe the timing mark you're looking at has moved.

 

On the low pressure - different gauges can read different pressures, due to internal volume variation.  Low pressure might not be relevant, but does fit changed cam timing.  

 

I'm a big fan of the notch and groove for checking that the cam and all of the other parts are in their proper relation to each other.  Does the Web cam not use the notch and groove?  Cam lobes up is not the most precise.  That's what struck me when I read your first post.  

 

Also, on spark - current through the coil will determine strength of spark.  Changing ignition system parts won't change power supply.  Maybe you've got a fried power supply wire to the coil and module.