Thanks Sam.

 

Hey Wshrdskin, That's funny that it ran that long, on engines with big HP you have about 6-20 seconds from the time you see smoke to big trouble in little China!! LOL. Have you ever had a needle valve stick and hydro-lock the engine with fuel when you tried to start?? Just another possability.

Someone asked if running high octain fuel in a low compression engine would hurt it. No it certainly won't hurt but if you run 110 instead of 91 in a low compression Rap (11:1) it will cost you about 1.5-1.75 rwhp. You can add ignition timing to gain most of that back but your cylinder pressure and temps will be about the same, so why waste your money.
Ray
PS here is a link to my web site and a video clip of one of our 686's on pump gas beating a 400cc Banshee, Ported, with CPI out of frame drag pipes, 15:1 comp ratio, 34mm flat slide carbs in a 300 ft drag.
Rap video
"Chris shee bashin" is the clip

 

wshrdskin Have you measured the wrist pins they keep getting longer from JE . I think the last JE failure had a wrist pin that was 2mm shorter than stock .
I wonder if they make shuttle components???[img]i/expressions/face-icon-small-shocked.gif[/img]

 

Never seen any smoke on the first or second piston. The first I just had oil coming out of the crank case breather, fir st a little then over the course of the 2 week vacation more and then the weekend at pismo enough to get real concerned and I was noticing a loss of power. I know I waited to long to get concerned, never said I was smart. [img]i/expressions/face-icon-small-blush.gif[/img] LOL. The second piston there was no warning signs like I was saying, it just died and before I was able to stop there was enough strokes of the piston left push out the oil from the crank case breather tube.

No sticking needle valves or flooded engines ever. I'm useing BSR 42 needle valve assemblies in my stock carbs also as the hole is much larger and will flow more fuel. I started doing that after the first failure along with jetting up 4 sizes incase the long up hill wide open throttle runs were running my bowls dry and causeing a lean condition.

Thanks for the ideas and help.

 

No, I haven't. I know JE made changes to the wrist pins. I don't know if the second one was an updated pin or not.

Ok, I just went and measured them both. I don't have a mm tape measure but the first piston wrist pin is 2 1/4" long and the second piston wrist pin measures 2 1/2" long. I guess the second piston was one of their updated versions.

 

That's really odd. I have never seen a piston failure that leaked cylinder pressure to the crank case but didn't suck oil into combustion chamber!!??!!
When we were having piston cracking on the stock car engines (on the shorter tracks) you would see a whisp of smoke under deceleration in turn 1 or 3 then a trail in 3 or 1 (opp corner) then before you could radio to shut it down, Ba-boom!! a big mess..
PS
The fuel requirements that I am recomending are for our climate, high humidity and no dunes. With dry air and long climbs, a bit lower comp ratio would be advised, but 11:1 is no prob on 91.
I'm gone for the night again, spent all day on the chassis dyno and half the night porting, now my head hurts, LOL
Ray

 

Well, I never look behind me when I'm riding and it didn't ever smoke on startup. Nobody riding behind me through the dunes or desert ever said I was smoking either. On the 1st piston I'd have to believe that there was some smoke as that quad was rode for a while before the repair. Just never saw it.

 

Depending on cam grind, you almost always have positive pressure in the cylinder. Even on intake stroke, the hole in the carb is bigger than the hole in the piston. This is depending on a lot the things like, overlap, and timing. But all in all, because of positive pressure, you would more than likely only see little smoke out the pipe, just like you said you did.
One time I popped a head gasket at 25 pounds of boost. Funny thing was, if I was in the throtle about 3/4 or over, it ran fine. Anything under it ran like crap. The reason, I found out latter, was because it would suck water into the cylinder if the hole in the carb was too small (no positive pressure). But under boost, no problems.
I'm working out your cc procedure for you, but I'm going to post it to a web page because it is 4 pages long!!! I will get to it ASAP.

 

Wow, 4 pages. Let me take the time to thank you for your time and efforts. Thats very generous of you. I appreciate it. Take your time. I won't be ready to put this back together for a week or two. I won't do anything more with it until this weekend. ie check the timing chain, flywheel key etc. The putting together process won't be until next week or the weekend after this coming.

Thanks again.

David

 

I would think if detonation was the main culprit once the piston started to fail it would go very quickly. Detonation on a weaked spot on the piston would just not last. That's another reason I think it's a flexing problem.

You would get smoke out of the pipe mostly on decell. but I think the rappy has minimal oil going to the bottom of the piston so you wouldn't get the smoke out of it like most engines. The lack of oil may be a factor with the cracking too (lack of cooling) as well as the rod problem.