I raced last Saturday night at Milestone Ranch. It was the first time they put us on the Pro track. Like any MX Pro track it's full of huge doubles and triples... not really great for Pilot racing. I had to brake hard for the first jump then nail it for the second... all the way around the track... WOT (Wide Open Throttle), Brake, WOT (Wide Open Throttle), Brake. Anyway, the Pilot ran great during practice. It ran great again throughout the first moto. But then... as I was cruising my way back to the pits, something seemed odd. The thottle response was just a little off. 30 minutes later, time for the second moto, I went to start it up and... I knew immediately... it was done. It cranked a few times but it got slower and slower. After a few tries it wouldn't crank at all. You could just hear it tightening-up...

Here's a few pics I snapped. The cylinder is on its last bore so I'm considering taking it to LA Sleeve. the crank needs to be rebuilt. Any suggestions from the So Cal guys out there on where to take bottom end? Thanks, Darin


//////////////////////////////////////////////////////////////////////////////////////////////////////////////////

Parts list (((don't ORDER ANYTHING YET)))

94301-14200 Pin A, Dowel (Dowel pin for Engine mount just need one)
90701-HE0-000 (Dowel pins for crank cases your old ones are stuck and will be junk when I remove NEED TWO )
91204-HE0-003 (Seal for the left crank case cover must have forgot to list this on the other order)
95701-06085-00 (bolt for recoil starter one is too short, its not the right bolt NEED ONE)


//////////////////////////////////////////////////////////////////////////////////////////////////////////////////

ATVR fail

No cooling holes drilled in the piston hmmm

Sure it needs a bore or just honed and a new piston?

Measure the cylinder for out of round and taper if in spec chances are its not worn since the last rebuild.

Why would you need cooling holes drilled in the piston for a pilot? I thought pilot jugs don't have exhaust bridges, therefore; no need for holes in the piston...

You don't see the bridge in the pics above with the scuffing above the bridge?

Its a CR500 cylinder he is running.

This top end was done 2 1/2 years ago at a Honda dealership... I was naive back then. I had very little mechanical experience and thought that I should trust the "pros". Thanks to this site... I've learned a lot.

You're right Hoser... The cylinder may just need to be honed. The crank, however, was stuck even after I removed the jug. It's moving now but... not easily. I don't feel competent enough to tackle a bottom-end rebuild. So, I'll pull the motor (( Internal Combustion Engine ? )) and take it somewhere locally.

I've never come across any discussions about drilling cooling holes in CR500 pistons. It makes perfect sense... Is it common? Any CR500 owners out there have any comments?

Oops... Somehow missed looking at that pic

No big deal it was a good question, your right the Pilot does not have a bridge and no holes need drilled.

Measure the over all width of the exhaust port if you can like in this pic.





The current piston looks like a Honda or PRO-X piston in the pics?

If the cylinder is ported and the exhaust ports are cut too wide you have to use the wiseco pistons because the cutouts on the sides of the cast pistons will allow a passage between the exhaust and the transfers.

Can you slip the cylinder back down over the piston then through the exhaust port take a scribe and scribe the exhaust port opening all the way around on the piston then we can see exactly how close to the cut outs you are.

If the bottom end is hard to turn its done don't run it!

I have the tools to go through the bottom end if you cant find someone local that's reasonable to perform the work, factor in shipping x2 if sent my way.

Any pics of the crank and rod ? Is their any discoloration?

Yes... It's a Pro-X.

I think you're absolutely right about needing to run a Wiseco piston. As you suggested, I slipped the piston back into the cylinder. When looking thru the exhaust port I can actually see the cutouts in the piston. It's not much more than a hair's width on each side but the cutouts are clearly visable.

Help me to understand what's going-on in this situation. It seems to me that fuel/air mixture is entering the exhaust port thru the transfers when the piston is near the top of the stroke. Then, the mixture ignites and causes excessive heat in exhaust port. Is that about right?

If the pressure in the pipe is higher than whats in the transfers (crank case pressure) then your going to have hot exhaust gases blowing into the transfers, see any signs of carbon in the bottom end or transfers?

If the pressure in the pipe is lower than in the transfers when the cutouts connect then pressure from the crank case will bleed into the pipe, this will reduce power because their is less of a charge in the crank case to be compressed on the next cycle.

The more pics you post the more we can help you.

Pics of the crank...

Whats all the dark specs I see in the crank case?

What clutch you running?

Any pics of the bottom of the cylinder showing the transfer ports?

The dark specs appear to be flecks of aluminum. There's a decent gouge in one area of the piston. You can see it in the attached picture.

The clutch is Power Block.

Cylinder pic attached.

Engine is here and apart.

Seal behind recoil was leaking balancer oil.

One of the dowel pins for Engine mount was crushed and will be replaced.

Not much metallic in the balancer case.

Welds part of CR500 mod

Crank seal on clutch side installed real deep

Cases split mad side bearing, see brown carbon trails on bearing race and bottom end

Rust on crank

Clutch side case

Better view on how deep the seal was set.

Seal full of dirt and crap, seal was bad letting in dirty and took out bearing or the bad bearing damaged seal and let dirt in, whats the history on this seal, looking at the seal leaking on the mag side I am under the impression these seals have not been changed in a long time???

Bearing stuck on crank, I will have to grind it off, the metal ball seperator all bunched up and wrecked, the resistance felt when trying to turn the Engine over was all the metal rubbing on the cases, it cut a trench into the cases where it was rubbing.

Instead of grinding the bearing completely off, we used to take a grinder and just cut 2 places in the outer race across from each other so that we could take a 2 jaw puller and grab the bearing in the notches with the puller and pull it off the crank...It's much faster and easier than cutting the bearing completely off with the grinder, and you don't risk damaging the crank surface....
Redman