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I have been working on a friends 1999 Honda Cr 80 he had blown the top end and had some pretty bad scaring in the jug so ....to save a few bucks he got a "2003 CR80" jug off eBay that had a new standard bore sleeve in it . The jug also came with a new piston and ring the ad says it is a Wiesco piston but its not. I'm not sure what brand the piston is but the old piston that i was replacing was a Wiesco and the two are not the same. so i checked the new piston with micrometer, it is 47mm standard bore just like the old piston. So i put the new piston and jug on the bike (bolts finger tight) and turned the motor over....no issues. So i torqued the cylinder and head bolt to spec and now the piston is hitting the head when i turn the motor over. If i loosen the head bolts it quits hitting. so either the piston is too tall or the jug has been shaved down too short or some thing .....i even tried putting two head gaskets on it and it still hits when torqued down???



so i guess im asking if any body has ever encountered this problem, and if there is any aftermarket head with a deeper combustion chamber that could possibly compensate for this, or if this being a "2003" jug does it need to use a "2003" head, i can take the cylinder back off and check the piston height compared to the wiesco piston that came out of it and see if they are different ...u know see if the piston is taller causing this issue ...but I've never seen a high compression Cr 80 piston and even if they did sell one it would have to work with a stock head to make the "high compression" right....not tap the head every time it comes up!!



please .....any suggestions I'm stumped :headscrat
 

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132 Posts
Discussion Starter #2
I have been working on a friends 1999 Honda Cr 80 he had blown the top end and had some pretty bad scaring in the jug so ....to save a few bucks he got a "2003 CR80" jug off eBay that had a new standard bore sleeve in it . The jug also came with a new piston and ring the ad says it is a Wiesco piston but its not. I'm not sure what brand the piston is but the old piston that i was replacing was a Wiesco and the two are not the same. so i checked the new piston with micrometer, it is 47mm standard bore just like the old piston. So i put the new piston and jug on the bike (bolts finger tight) and turned the motor over....no issues. So i torqued the cylinder and head bolt to spec and now the piston is hitting the head when i turn the motor over. If i loosen the head bolts it quits hitting. so either the piston is too tall or the jug has been shaved down too short or some thing .....i even tried putting two head gaskets on it and it still hits when torqued down???



so i guess im asking if any body has ever encountered this problem, and if there is any aftermarket head with a deeper combustion chamber that could possibly compensate for this, or if this being a "2003" jug does it need to use a "2003" head, i can take the cylinder back off and check the piston height compared to the wiesco piston that came out of it and see if they are different ...u know see if the piston is taller causing this issue ...but I've never seen a high compression Cr 80 piston and even if they did sell one it would have to work with a stock head to make the "high compression" right....not tap the head every time it comes up!!



please .....any suggestions I'm stumped :headscrat


here is a link to the cylinder i bought

www.ebay.com/itm/2003-new-cr-80-cyl...6kkwSjD426I9oaE%3D&orig_cvip=true&rt=nc#rpdId
 

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The '03+ bikes changed to 85cc, using a 47.5mm bore instead of the 47mm bore of the 80cc bikes. Are you positive the bore is 47 and not 47.5? A 47.5mm piston would hit the squish band of a 47mm head.

If that looks in order, it's time to start measuring some parts. The height of the pistons and the height of the cylinders themselves. It is possible that the '03 cylinder had the base turned at some point.

You have several options depending on what you find. If the head is the issue you can send it to a builder and have the chamber and squish band modded to work. You can also stack base gaskets to get the cylinder up some. Don't stack head gaskets, those metal ones aren't the most reliable things anyway. Cometic makes an aluminum/foam base gasket in .018" and .032" thicknesses.

You want no less than .024-.025" squish (distance between the piston and head).

A trick on the head gaskets is to hit it with some silver spray paint and let it set up for a few minutes before assembly.
 

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Squish is normally adjusted with the base gasket, you should be measuring it and adjusting it.

Even a brand new kit from alpena comes with several different base gaskets.
 
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