Hole in my Piston??

[MadMax]

Hi Guys,
I was having this funny problem with my engine only running if I set it at 38° or more BTDC timing. It didn't run very well, but OK, I drove like a hundred miles with it. Now a few guyes told me, that setting my engine so far advanced would burn a hole in my pistons "real fast". How do I tell If I have a hole in them? It runs better now (got the valves properly set, before some didn#t quite close) And I don't want to take off both my Heads to look at the pistons. Will pressure checking be enough to find out whether my Pistons are damaged? They were new stock Pistons. Can anybody help? THX!

[Gorn]

You would know if you had a hole in your piston cause of the smoke. I agree with your friends. Sounds like you might a fuel mixture problem that is forcing you to advance the timing to get the car to run right. Does the car ping? (you know rattle under load).

[MadMax]

Yeah, it does ping a bit, if I really step on it. I don't think I've got a hole in my piston, as I say, it runs and all cylinders fire, I guess there would be even more irregularity if I had a blown Piston. I'm running with 91 octane fuel and a stock 350, stock cam, stock everything except for Edelbrock Performer Carb and Manifold. I guess I'll just give it another try, after all you learn with every mistake you make. But I damn well feel like I'm learning a lot these days ;-) Will changing the fuel make very much of a difference?

[junior]

too be sure do a compression test , or a leakdown on the cylinders . that will tell you if you got a hole in anything .

[pro70z28]

I agree with Junior. I would hunt down the ping problem A.S.A.P.

[BlueDSM]

If theres a hole in the piston, your compression readings will be zero or extremely low, and your leakdown will be large.

Something is odd if it only runs at that timing, is it possible that the timing chain may have skipped a gear, or the cam timing was modified?

Pinging only happens when you have a lean mixture under load, or are using a low octane fuel that detonates easy. Raising the octane basically increases the fuels resistance to pinging, so 94 octane should lessen pinging (it has in my cars when I wanted to run more timing or boost).

Thats all I can think of now.

[tjpoc]

Junior's got the answer. If there's a hole, you'll know it by zero compression in that cylinder or with a leakdown with a very high loss. Another thing to consider if you think you've damaged something is you could have wiped out your rings. Pre-det could blow a hole in your rings giving a similar result.

Buuuuuuttttttttt, why do you think you have a hole in the piston? Do you feel the engine missing on a cylinder or are you blowing smoke out the exhaust? Do you have a lot of crankcase pressure (oil or air blowing out your breather cap)? Your timing is a little high, but if you didn't stomp on it and let it ping itself to death, you should be okay. Focus on the fuel / cam / timing chain to get the timing to a more reasonable level. If you're a tooth off on your chain and gears, the engine may still run, but you may have to adjust the timing to get it to idle.

When you say new "stock" pistons, what does that mean? Cast or Forged? Forged can withstand more abuse and are not likely to be damanged by a few miles of pre-det. Cast may get pitted quicker, but in a hundred miles, it would be hard to say they are burned up. Advance in your timing doesn't burn a hole...premature detonation or a super lean mixture of fuel burnes the holes. Like if you use heavy nitrous with a weak fuel charge. Doesn't sound like you did any of that...yet!

[MadMax]

Hi tj!
No, I'm not running any nitrous. Don't need to either as I'm not in the racing business. I seem not to have damaged anything. I just readjusted my valves, now I've got the timing much better and it runs nicer, too. I just wanted to hear a few opinions on if I might have damaged something, before I give it a test run, which might ruin a lot more if things are damaged. And to tell the truth, I don't know exactly what pistons I have, I bought the engine second hand and the previous owner only knows that it was newly rebuilt in '99 and had only travelled a few thousond miles. I took one cylinder head off once to change a gasket and the pistons have those "eyebrow"-cavities for the valves. but I don't know if they're forged or not. How can you tell that? would be interesting to know...
THX again!

[73RS]

Are you setting your timing at 38 degrees btdc as total timing or is that initial timing? If initial that is way too much, you shouldn't go over 40 total as a max, usually a total of 36 is where you want to go. Initial timing can vary a bunch depending on how much total advance your distributor has, you need to know that to really set your timing properly. You can also get one of those dial in timing lights to get your timing set or put some timing tape on your harmonic balancer.

[tjpoc]

Hey Mad,

Have you tried a higher octane fuel? Like 92? You can get pre-det from a number of things, like too advanced timing, burned valves, low octane fuel...and so on. If you run a heavy vehicle, that can affect timing also. If you think you've damaged something, look for the smoke.

Re the pistons...it can be difficult to tell what they are. A cast piston is typically dull grey (like the background on this post). A forged is often shiny silver and generally you can see machine marks cut into the top. In either case, if you're not in the racing business, cast will work just fine. Either can have the eyebrows.

Good luck,

tj

[MadMax]

Hi Tjpoc and 73rs,
I think I'll just try some higher octane fuel. The normal stuff you get round here is 89, and there's 91, 95 and 100, but they get more expensive, of course. I've been running on 89 so far and it is a heavy car. I'll just give it a shot. The pistons are a sort of dull grey (that's what they looked like when I replaced the head gasket) but that might also be some carbon on them. I would think (judging by the rest of the engine) that I have which ever ones are cheaper ;-)
It's been running for some time again now, and I seem to be getting better timing out of it, I've made different marks on the balancer, so I can tell how it's set. I don't have a dial-back-timing light, but I guess that will be No. 1 on my BUY-list. Thanks for helping me out so far, I guess I'll be back to report how I'm getting on.
CU, MadMax.