kb 40 sleeve question

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kb 40 sleeve question

Postby robhinze » Tue Jun 02, 2009 7:44 pm

I have an old .40 that was made back in the mid 80's. Sat in storage all these years. Engine was very stiff from the old fuel and etc. Took it apart and noted rust/gunk in rear bearings. Cleaned out with PB blaster (antiseize spray) now the crank spins free. Slipped out the piston and buggered the ring while trying to slip back in with out cleaning from the top (Doh! New one orderd) The piston sleeve and block had to be heated to 380 degrees in the oven for 20 mins to be pushed out of the block.
My question is this..Should the sleeve just slip back into the block? Or will I have to heat the block and freeze the sleeve and piston to re-instal. Does the piston always have to be inserted from the bottom of the sleeve?
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Re: kb 40 sleeve question

Postby Arctic Cat Rider » Wed Jun 03, 2009 6:18 pm

robhinze wrote:I have an old .40 that was made back in the mid 80's. Sat in storage all these years. Engine was very stiff from the old fuel and etc. Took it apart and noted rust/gunk in rear bearings. Cleaned out with PB blaster (antiseize spray) now the crank spins free. Slipped out the piston and buggered the ring while trying to slip back in with out cleaning from the top (Doh! New one orderd) The piston sleeve and block had to be heated to 380 degrees in the oven for 20 mins to be pushed out of the block.
My question is this..Should the sleeve just slip back into the block? Or will I have to heat the block and freeze the sleeve and piston to re-instal. Does the piston always have to be inserted from the bottom of the sleeve?


Use some fine emery cloth (like 400 or 600) to clean the outside of the sleeve, and the inside of the case. You do not have to heat it up to re-install the sleeve. You will have to coax it a little, it's not a "slip fit," but it shouldn't be much of a challenge.

You will install the piston and con rod, connected to the crank, before you put the sleeve in. This is the only way to do this. Otherwise, if you put the piston in after, you'll never be able to slip the big end of the conrod over the crankshaft pin. There's just not enough rooom.

Put the piston and rod assembly in, turn the crank to top dead center, or bottom dead center...whichever one is easier for you to slide the sleeve over the ring, and piston. Just be easy on the thing....if you start to get impatient, put it down for a while and revisit it later.
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Postby MECOA » Wed Jun 03, 2009 7:26 pm

Actually you may have to heat the case a little to make it easier to slip in. Only about 180 degrees.

NOTE to Artic Cat Rider - the 40 has a bolt on front housing so the piston does not have to be installed on the crank.

You can put the piston/ring/rod assembly in the sleeve after the sleeve is in the case and push the crankpin into the connecting rod while it's all in the engine.
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Postby robhinze » Wed Jun 03, 2009 9:03 pm

What is the best way to compress the ring on the piston head? Before the piston had some crud in the ring groove and I did not get it compressed enough. This resulted in a damaged ring and ego.
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Postby MECOA » Tue Jun 09, 2009 8:23 pm

It doesn't get compressed into the head. It gets compressed into the groove and then into the cylinder. You can put it in from the bottom of the sleeve to. There is a slight taper there that will help it into the cylinder.
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