Vintage Dirt Bike Q & A

Started taking motor apart with intentions of new crank bearings seals, rod and bearings because I had a seal leak on the clutch side.(Don't know previous history on motor)
Now that I got it apart, crankshaft feels real tight, both sides and is smooth on rotation, no noise. Everythings off but cases are not split.

So I thought I would just put in seals, BUT, my side to side big end on the rod clearance is .027 and service limit is .028. Rod big end up and down has no play.
Do you guys think I can get away with running a new piston through this motor and then when that piston is done, split the cases and do it all then? Don't really wanna split cases unless I have to. This is a back up bike so I was thinking I could get through this summer with it just doing the clutch side crank seal. Gimme you honest opinion, thanks garry

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Garry Mainer
#33m (retired)
Honda Cr250r 1980
Honda Cr250r 1980
Yamaha TY250C 1976
Arctic Cat 650 H1 2007

My inclinination would be to RUN IT! You're still in specification and the maximum tolerances are usually set on the very conservative side.
I'd worry about it more if the small end of the rod had a problem.

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1978 CR250R
1979 CR250R
1980 CR250R
1980 ME360
1986 CR250R

If there is no up and down play in the big ends or the crank bearings, I say run it...

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

Thats what I needed to hear! Gonna go order me some crank seals.

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Garry Mainer
#33m (retired)
Honda Cr250r 1980
Honda Cr250r 1980
Yamaha TY250C 1976
Arctic Cat 650 H1 2007

Barry, I have been a motocross mechanic for over 25 years and my opinion is I would not run that rod with those limits. A new piston will put alot more pressure on the rod and will almost always take the rod out. Alot of people don't relize this but it happens alot when they tend to freshen up a top end with not adressing the rod. Later Randy Sorry I know you did not want to here this.

You could send the engine to http://www.racerstoystore.com. They put IMS hot rod kits in both my engines and replaced the mains and seals. If you are told elsewhere that the crank and rod are only available as a single - expensive - unit, that is true, but a rod kit from a 1984 Honda ATC250R works fine. Send it to someone who has done this before.

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

Thanks for the advice Randy, you are probably right, but we are gonna run it. Chances are it won't get rode much anyway if at all. Then this coming winter, I'll make the changes when I have more time.

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Garry Mainer
#33m (retired)
Honda Cr250r 1980
Honda Cr250r 1980
Yamaha TY250C 1976
Arctic Cat 650 H1 2007