engine valve to piston clearance problem

Tearing down the Fly to find the ever ellusive "Gremlin". Upon disassembly we found a couple of pistons that have had an ever so slight "kiss". The top of the piston has just grazed a valve. This is evident in 3 cylinders. When I say grazed, it barely polished the carbon off the pistons.

Now I understand we have an evident problem but here is my actual question.

Would or could this cause the stutter that I had upon launch?

The stutter would appear after 60 feet or so for approx. 1 second then run like gangbusters. We changed every component known to man and still no change. Could this be our problem?

The mystery cam that has been in the car from the beginning is going away to try and alleviate any unknowns.

 

If it ran decent other than the stutter, I'd throw a little thicker head gasket on it and give it a run.

If the problem goes away, you found it, if not, you didn't!

 

I just wonder if the rods aren't stretching....

 

With a powerglide, I don't think so. The valve contact with the piston crown is most likely at max RPM, when the valves float a little. Most 'glide cars don't reach that point until the shift or the lights, and either of those are usually downtrack from the 60 foot mark.

Not that I am an expert, but I would guess maybe a mixture problem. Those Hilborn injectors are not known for precise mixture control over a broad range of engine speeds. Of course, the ever-popular ignition problem could be the culprit.

 

I thought it was ignition myself, that's why I sent the mag back afetr having it overhauled. Then I tried another mag, then an HEI. 2 caps, 3 sets of wires and 4 different sets of plugs.

 

What are you gapping the plugs at?

 

.016"-.025"

 

What are you running for fuel distrobution? Sorry for being stupid, I haven't been in on this build.--TV

 

Hilborn injection

 

my .02 cents,

Is it possible with that shallow of a plug gap you are "washing out" the flame, a.k.a. the flame is being knocked out? I know with an H.E.I. recommended gap on plugs is usually around .040 to .060 even. If you are running a good aftermarket coil I would open that gap up a bunch. With an aftermarket hot coil I have run .065 gap with zero probs before. Bone stock most are gapped at .045.

Hope that might help

Scot

 

With the HEI we gapped at .045".

Magnetos need a shallow gap for starting.

 

I had that to happen with the va;ves kissing the pistons and found some sloppy valve guides. It might be worth a check. Good Luck ,Hooley

 

We (Champion Racing Division) recommend .018 - .022 for a Magneto ignition depending on a llot of factors. Infact, we have most Nitro engines running .012-.014 right now.

With other (MSD, Crane,Jacobs) race ignition systems, we recommend .026 - .032 MAX in race engines.

Larger gaps than this the turbulence will blow out the spark, proven fact.

I do not feel that the issue you are having is ignition related, I believe from what I have read on your combination, it is fuel transistion related.

 

Glen, we went there after the ignition.

I changed 1 used injector pump, then we bought a brand new one.
Changed fuel nozzles,2 sets of lines and injector lines. Converted to methanol. Changed barrel valve settings from 1 end of the spectrum to the other.
The only component left is the barrel valve, which may get changed just for grins.

I am sending it off to have it flowed although I don't think they will be able to tell us anything we don't already know.

I am suspect still of the ignition possibly arcing to the header tubes. We are gonna build a new set just to gain some boot clearance.

It is REALLY getting old trying to troubleshoot this pig. I know you guys are tired of hearing about it.......but my wife doesn't care.

 

Other than this 'stutter' that takes place momentarily ofter launch, the engine performs like you expect, correct??

This 'sutter' never happens with the engine unloaded (out of gear ) or under a 'drive-up-through-the power band like on the return road, right??

 

I love that car! A kiss is just a kiss. When the valve JUST kisses the piston (for whatever reason) all it's going to do is polish/rub off carbon. It's indicative of a narrow margin that may need to be attended to, but not the cause of your problem. I don't know dick about fuel injection (but, one day i'll try this type setup on the street), so that's the extent of my 2 cents.

 

No, it's crazy Glen.
It launches pretty decent then about 20 ft out it falls off a little and starts missing. Then it clears up and runs on out. The best we could get was like a 12.59 at 107. I have a video if ya wanna see it crapping on itself....

 

yeah, email me the video

ahotrod@bellsouth.net

 

Here it comes....BIG FILE.

 

just a guess....but how is the return line run ...? brandon

 

straight run about 3 ft long, 1/2" ID hose.

 

what i meant was ...how is returned ....into the supply line or back to the tank ...? thanks

 

The way injectors work is that in the return line there is a "pill box" that has a metered orifice i.e. jet, and the amoutn of fuel that returns to the tank is actually what meters the fuel.

So it goes straight back to the tank with whatever the engine doesn't need.

That prolly made no sense.

 

Glen, let me know if ya get the videos. They didn't bounce so I think you should get em.

 

the reason i was asking ...a buddy was having similiar troubles with his pulling tractor.....the fuel was being returned to the supply and was sorta goofing up the supply......he switched the return to tank ....to the top and showering in ....the guys at ron's figured that problem while talking to them at the pri show...must have worked as he didn't have any troubles after switching......brandon

 

Had a near identical problem with our first Hilborn engine a 292 SBC in a gasser years ago.The problem turned out to be unequal air flow between the cyls at idle and small throttle openings.The fuel delivery is equal so if the air flow is not we see some slightly flooded cyls on the ones that are not getting enough.This is affected bank to bank by the cross linkage including the clamped on arm angle, and cyl to cyl on a bank by the fit of the butterfly in the bore.
I wound up balancing these using a uni-syn meter that we used on the old multi carb setups like Jag, MG,Healy,etc.
A small unbalance caused us the problem that you describe.Had a heavy wheel and low gear so came out of the hole pretty strong but stuttered as though rich for a little then cleaned up and screamed on through.
These butterflys don't automatically center up in the bore when the screws are tightened but have to be helped to align with your fingers and by tapping with a soft rod or screwdriver handle.
I placed the uni-syn on top of the stacks or base one at a time at idle noting the ones that flowed high or low so I could readjust.Good luck

 

Interesting.....Thanks.

I have reset the butterflies to make sure they were closing the same. The gap is matched, but the thing is we have never adjusted the cross linkage. Hmmmm.....

 

Got 'em ! ... and responded to your emails.

 

Thanks.

 

Rooter.....I ain't got a clue but I love watching you and yer dad work on it.