possible 350x preignition?

[camoweasel]

To first start off, I do understand the theory behind octane and detenation, so I'm up to snuff that idea. Basically, my question is what does pinging sound like on a single cylinder ATC engine? I just finished rebuilding my top end with an oversized 10.25 piston and a ported head. I am noticing a very faint sound right when you first accelerate from a stop and when you bog down the engine down. It almost sounds like a very very quiet tinging sound like hitting a machine screw against a brake drum, but very quiet?? For some resaon I guess here things that most poeple don't so it could very well be in my head. I did notice the head gasket I used was thinner then most head gaskets I've ever used?? It came with the rebuild kit I bought from G&H ATV supply in Tennessee. It's a brand I never heard of but seems to be working fine. But other then that the engine runs great and sounds good overall. I am running 93 octane as we speak but I just never heard a single cylinder thumper ping or pre-ignite before so I don't know what it sounds like??

[Dirtcrasher]

You may have higher compression than you think and hearing detonation...........

Should have been a 3 layer head gasket. Or run race gas and rejet which I've found to be a PITA.

[camoweasel]

DC, The versah headgasket I used before was indeed 3 layers thick. The brand name kit I used came with my remanufactured cylinder I sent to G&H ATV discount supply to get bored. It was a weird name that I've never heard before. I'm trying to remember but I am almost positive, it wasn't as thick as the Versah. I've heard plenty car engines ping before but not a thumper engine so I don't know what listen for. Like I said, it's very very faint but most noticable accelerating from a stop and when the engine is lugged in a higher gear. It may or may not be jetting issue but I am using 93 as we speak. Next week, I will be making a trek from PA to FL, to do some riding with a friend, so with the hotter weather I will encounter i want to be sure the issue can be resolved.

[SWIGIN]

What piston are you running?

[camoweasel]

I'm using an 81.5mm WIseco 10.25 compression piston. Next oversize to stock.

[beets442]

What does the sparkplug look like?

[camoweasel]

it looks normal to me. A little grey but no signs of pre-ignition.

[Dirtcrasher]

Whats the compression at?, don't forget to disable the cable.....

[camoweasel]

Well that may be tough to find out since I don't own a compression gauge. I'll see if I can borrow one from somewhere and get back to you.

[camoweasel]

Doubt that I'm going to find a compression gauge before this weekend. Here is an easier question: What does pinging or detonation sound like in a ATC thumper engine?? I'm half tempted to mix half 93 octane pump gas and half 100LL fuel in a 5 gallon can and try it once??

[SWIGIN]

From my experience with 350x motors, pinging sounds like a valve tap and it's very loud. But is'nt this the motor that the guy had the rings on wrong? If so that sound could be anything. try the race gas mix but with your piston it should run fine on 93.

[bcredneck]

swigin is totaly right when i first got my 350 i used 87 it pingd like crazy loud i drained my tank and used 91 no sound

[camoweasel]

From my experience with 350x motors, pinging sounds like a valve tap and it's very loud. But is'nt this the motor that the guy had the rings on wrong? If so that sound could be anything. try the race gas mix but with your piston it should run fine on 93.

Good memory there. But no it's not, I got all my stuff out of his shop and started over but this time I did it myself with a friend who knows this stuff. He made sure I didn't do anything wrong, and it was a great learning experience. The original cylinder had some scratches from the last yahoo, so I sent it away to have it bored to a specific next size wiseco. Everything came out really nice and sounds good. I'm just not sure if I am hearing pinging. It's very faint tingy sound but most audible when first starting out accelerating and when the engine is lugged out in a higher gear. It's definitly not valvetrain noise cause, I just adjusted the valves and the cam chain is brand new. I may try some 100LL since I will be treking to Florida (sea level and warmer) to see how it reacts to the weather.

[Flossyb20]

I would double check the carb settings..maybe your needle hieght is not adjusted properly. I sounds like when you first open the throttle, the engine "bogs" down for a 2nd before running right (the ping). Had the same issue with mine, and I thought the same thing you did, but come to find out my main needle was set too high. Hope this works for you, as it was a pretty simple fix.