I recently bought a 1988 250r from a buddy that he was having trouble getting it to kick start it came with a 1988 310 engine and the engine on it is suppose to be a 1986 with a 265 kit I tore the engine down and the exhaust side of the piston was missing I was thinking that it had a blowed head gasket and it caused it to melt the piston but I’m not sure the engine has a spacer plate under the cylinder so I’m assuming it has the long rod in it but I’m not sure I cleaned the cylinder up and it seemed to clean up nice so I was gona put a new piston and rings in it but I’m not sure what year piston to get I googled the numbers on top the old piston and came up with a 68 mm wiesco 1986 piston but I was just wanting to try make sure that was the year piston I needed and the reason tgat it broke or melted was not because someone had the wrong piston it any advice would be greatly appreciated
250r piston help
Justin335
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before you go and order something, you need to determine your cylinder clearance. Just putting another 68mm piston in there may be a short term fix if there is too much cylinder clearance. The piston skirt will break and potentially trash your whole motor. The next size larger piston is a 68.50, 526MO6850 for wiseco. plenty of them for sale on ebay. However, once you go past the 2mm overbore (68mm) the standard headgasket will not work and ideally you would need to get your head rechambered to account for the increased surface area now part of the chamber on a 2.5mm overbore.
no quick fixes if you want it done right.
also you have a long rod per the HA2, so use the spacer plate with the 85/86 250r piston
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you dont. take cylinder and old piston to a quality machine shop to have them measure. Like a place that would build a performance auto racing engine, if you dont have a good local dirtbike repair shop. You want clearance in the 0.0035-45 range. maybe a little bit more figuring some might be worn off piston as well as the cylinder.
K we don’t really have any shops around here that build race engines we have a Honda dealer I will go in there tommorrow and c I’d tgey can check it out for me does anyone have a head gasket recommendation for the 68 mm or would stock b fine
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as other said you cant just order a piston and hope it works.it need the bore checked then usually a larger piston needs ordered then they bore and finish hone for new piston.if you dont have a shop around you send it to a shop.as for headgaskets oem is pushing it with a 68mm bore.and anything bigger the head gasket also needs bored...bdt motorsports can do all the work and also has the needed headgasket in stock.
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1,608 Posts
This is how I ID OEM stock crankshafts
KA4 1985 Honda ATC 250R Short Rod
HA2 1986 Honda ATC TRX 250R Short Rod
HB9 1988-1989 Honda TRX 250R Long Rod
Now 1987 I really don't know much about that year was already morphing into an 88 so it has many differences from an 86 and allot of similarities from an 88
Good luck
KA4 1985 Honda ATC 250R Short Rod
HA2 1986 Honda ATC TRX 250R Short Rod
HB9 1988-1989 Honda TRX 250R Long Rod
Now 1987 I really don't know much about that year was already morphing into an 88 so it has many differences from an 86 and allot of similarities from an 88
Good luck
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lean.not enough octane fuel for compression.
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I'm guessing that your engine has an air leak like crank case seals. Other than cleaning don't mess with the carb. Do yourself a favor and research for a local mechanic and request a leak down test after rebuild. It will save you money in the long run.
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The leak would be on the intake side which includes the crankcase on a two stroke. Leaky crank seals seems to be most likely. I don't know and know one can without getting hands-on. If your goal is running 250r on a reasonable budget a local mechanic will be able service you and your 250r best. If your budget allows send your complete engine to a respected builder.
K so I got my piston and stuff and was checking on crank seals and noticed there is oil where the crank and rod is every time I turn the crank over it will come up with oil on it so I am assuming the crank seals have to be bad I have the other bottom end from the 88 motor if that will work but if it’s not a really big job I was thinking bout putting the seals in the 86 motor if I don’t have to split case or anything does the case have to be split for the seals to be replaced
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