Piston and cylinder wear

[kiesta00]

Hey guys I had my stroker motor put together last February and I blew a head gasket this weekend and got coolant in the crankcase, so I had to pull the topend off to get it out. I noticed the piston and cylinder has some wear marks on them on the exhaust side. Is this common among stroker motors?

http://i70.photobucket.com/albums/i106/kiesta00/DSC00449small.jpg
http://i70.photobucket.com/albums/i106/kiesta00/DSC00452small.jpg
http://i70.photobucket.com/albums/i106/kiesta00/DSC00454small.jpg
http://i70.photobucket.com/albums/i106/kiesta00/DSC00447small.jpg
http://i70.photobucket.com/albums/i106/kiesta00/DSC00445small.jpg
http://i70.photobucket.com/albums/i106/kiesta00/DSC00446small.jpg

[regg187]

Ok, I'm gonna give my 2 cents, Exhaust side seizure (milld) 2 oiler holes drilled in the piston, and big wear on the piston in the center of the exhaust port. Not a 4 corner seizure.
I'm guessing the Exhaust port is pretty wide on the BB, I didn't see a bridge in the EP. Piston getting Too hot and bulging into that wide EP ,bulgin reaches its max in the center, of course thats why theres a nasty line in the alum piston (soft). but the motor builder must know this thats why there are oiler holes right in that exact spot. I'm thinking maybe a little lean on the top end jetting let this motor heat up beyond whats "norm". or maybe a small air leak leaned it out. Do you have an oversize Rad on it. I know they recommend that on the bigger motors.

What ever.. my diagnosis is she got too hot. fix that and you'll fix your problem.

Remember this is only worth 2 cents.

[kiesta00]

It never seized up...it was running great until it blew the head gasket and got coolant in the cylinder and bottom end...

The bike ran hard as hell on alcohol until it blew the hdgasket, I had the compression at 215psi. I may just switch to a pro-x 310 thats for sale on a forum instead of fixing the stock cylinder setup.

[GPracer2500]

Looks like the exhaust bridge may not have been properly relieved. I'd guess that wear pattern developed on the piston soon after it ran for the first time up to full temperature. But the bridge-to-piston contact wasn't bad enough to cause a full seizure. They just clearanced themselves, essentially.

From the OEM service manual, page 1-15:
http://i34.photobucket.com/albums/d133/gpracer2500/bridgerelief250r.jpg

The bridge needs a little extra clearance. Since it sits in the middle of the exhaust gas flow and has little means to transfer heat to the rest of the cylinder, the bridge gets hotter and expands a bit more than everything else. So, it needs a little extra room to expand into.

The oiling holes are standard items on all Wiseco pistons used with bridged exhaust ports. The holes help maintain the bridge's oil film to keep it and the piston from actually touching. Some Wiseco's have the holes drilled by Wiseco (as is the case for the 250r) while other models that share pistons with non-bridged cylinders require the piston installer drill the holes.

http://i34.photobucket.com/albums/d133/gpracer2500/WisecoholesLarge.jpg


So, that's my $0.02. Hey, now you've got $0.04 worth of reasoned guessing! ;)

[regg187]

Yep, 3rd picture , missed it ,

:mad:

:o

there is a bridge in there, not releived enough, but on the cylinder wall there are marks beyond the bridge. It did seize , just not enough to lock it up or those marks couldn't exist. marks= metal to metal contact=seizure. when it was bored did they stick to the very minimum side of the clearences or just slightly under, it might explain the marks, you said it was on alcohol before, they run much cooler, so it is reasonable that they ran the clearences tighter, because of this.

NICE CALL GP2500!

now it's up .05

[86 Quad R]

yup..... i'll third that. deffinately from the exhaust bridge not being releaved enough.