CR 500 jetting issue

same here, i have fitted 3 now that have a good amount of service time and are wearing great. i do like the original mahle too, cant go wrong with those.

Never had a Wossner problem here. Air cooled 101: Ring gap and enough jet.

Hello Mate,

I've spoken to Andy and I'm having it honed out to 95micron clearance (approx. 0.0004") I think part of my problem is that I used to run the 500's on a blend of 60% 97 octane with 115% Octane Sunoco fuel to give me 105 octane. The 115% Sunoco stuff has lead in it, which helps keep it a bit cooler. I stopped using it as it was bloody expensive, but I might have to have a re-think.

I've got a 44mm carb on my Silverstreak, but I've not ridden that baby yet (probably wont ever ride it lol)

Steve

ive seen a heap of 500 woosy's seize on the box specs. i also note that they were fairly new engines (1 or two tanks) put into high load situations. deep mud, lonnng straights not enough enough jetting time etc

What sort of clearance is need in a 82 500 with a Wossner. Stock everything else . Ran fine . Just worn out the old piston

I've been told to use 95 micron (0.0004") clearance on the Wossener pistons. Ive also ordered some more leaded Sunoco 115 Octane fuel to hopefully cure my issues.

May want to move that decimal point over one. To .004 Because of heat of texas bored out a bit more .0045 now

So Steve are you saying you are adding a overbore or honing out to .0005 more to clean it up?

I was amazed also when I had the timing just a bit past or advanced on how hot bikes run

Timing being just a little bit too far advanced can a lot of heat for no real performance gain. On a water cooled bike it can dissipate most of it, but it can be very bad for an air cooled bike.

sounds like different advice than what most of us do. but our bikes still live somehow.

I'm just honing to clean off the aluminium coating I got when she nipped up. The thing only seized at the end of a long straight. By the time I knocked her out of gear and got the kick start out she kicked over again and fired up. I have always run stock timing, but I will double check that I'm on the dial. Plus as I said I'm going to run blended leaded fuel. It's going to be a couple of long nights to get her built back up before we leave for the biggest twinshock event in the world on Thursday...Farleigh Castle Vets Des Nations.

The exhaust will run hotter but not the engine because retarded timing has the fuel charge still finishing combustion after it has been pushed out to the header. Timing that is too advanced has the fuel charge burning and expanding too soon before TDC which puts the heat into the engine, not the exhaust.

She lives...3 hours and she is back together and running again just in time...

Good luck at Farleigh Castle this weekend, weather forecast down here doesn't look too bad!!

Why are there so many seezed ?
I think we're getting mixed up. Advanced is before top dead center, retarded is after top dead center,

yup, thats advance and retarded spark timing.....you could be getting mixed up, im not sure. many of us retard our bikes a bit for several reasons. saying it makes the engine run hotter is not a grasp of 2 stroke operation theory. there are few seizes here on cafe, mostly because we usually dont report "hey my bike ran its 10th tank of fuel no problems again" for no reason...but if someone has engine troubles we talk about it i guess..
seizes are usually jetting and bore clearance imho. i run my stuff somewhat hard and have never had it happen.

Anyone who's worth using will know what to bore it to regardless . Problem solver . Let the engine builder do the engine building

No one is confused. His point is you say retarded timing causes excess heat, which is only true if you are talking about exhaust temps, which is irrelevant to piston seizures, too much advance causes ignition of the fuel charge too early which dramatically increases cylinder head and cylinder temps which is directly related to what we are talking about with seizures.

The single most common cause of a seizure in a two stroke, of any kind, is an air leak which probably covers 75-80% of them, the remaining are jetting, ignition, tolerances, etc.

No don't use the advice of most engine builders. Do use the advice of Husky engine builders.

Most of top posters here build their engines and most tell the machinist their needs based on
true experience

So sorry - say it ain't so Joe - you will be missed

I agree, when I take a cylinder to the machine shop I give the machinist the specs I want

Well you guys need to find more knowledgeable machinists