lapping head to barrell and piston bore clearances

Hi guys,
the XC 250 1983 I bought had a new head and has not been run, what is the procedure for lapping head to barrel.
Also what clearances do you recommend for piston bore with the wossner, what they recommend ???
Thanks in anticipation

what wossner recommends for the 250 is fine, or has worked for me at least.
as for the lapping, pick up some lapping compound and apply a small amount to the top of the liner. set the head on, and using light hand pressure, twist back and forth a few times. wipe the compound clean enough to verify the compound has done its job. it will take 2 or 3 times but you want to see a somewhat uniform ring the whole way around the head, showing a good seal. you dont really want to do more than whats needed. after this is done clean it all up very well and reassemble. do not use any type of compound, just bare metal between head and jug. obviously you will need to pull the cylinder and head to perform this. good luck!

oh, and you better get a rest for that kicker soldier! dont let that foot slip off!!

check that the head bolts are not longer than the threads in the barrel....have seen them bottom out just on tight but allowing air in once hot with seizure . took 3 pistons to figure it out

If in doubt, add 0.01m/m to the recommendation. Don't forget, that when a cylinder and piston are worn - it is usually by about 0.2 - 0.3 of a millimetre!!!

In the UK - we think probably due to the recent lowering of fuel quality (10% of pretty much all UK fuel is now Ethanol), we have had reported to us a spate of 430 seizures - bikes that were perfectly happy on the old fuel.

Andy

ETHANOL SUCKS

Hi guys,

Thanks Justintendo for that I was a little surprised that no head gasket existed when I stripped it down. Your not far from where I got my bike (Indiana, Carmel).

Thanks Surprize, will no doubt see you soon maybe Beaufort again. The XC is all in pieces and Geoff M doing some minor welding and frame improvements. So I will on KDX 250 if I finish that. Will check those bolts, especially now that they have been spot faced thankyou thankyou thankyou. I am not dislectic.

Thanks Andy. I also have a 2010 WR 125 (now a 165 thru Walt Smith (this forum)) and the head has been back to the usa once for further relieving and it still pings and this is because Australia has shit fuel as well compared to the US. They have like 100 octane pump gas and I thought we had 98 here but its not the same. I need to use an octane booster for 165 now.

Thanks troy. Missouri well that's a great place to live, (Mark Twain National Forest) I was going to ask where the hell is republic MO and then goggled, I was expecting Uzbekistan or somewhere eastern Europe not Springfield Missouri.


Anyway thanks Guys

your welcome

I use valve lapping compound to lap the head to the cylinder for the perfect seal. This should be done on everyone we take apart for a refresh. Just a little lapping will do. Try to put an even pressie around the top of the head when lapping it. There's two seals on the top of the cylinder with a tiny space inbetween. I make sure both seal lines are in the head all the way around and these two lines are clean on the head. You need a 360 degree seal.

Seek perfection for the perfect seal.

The '83 250wr husqvarna milk truck surely delivers it was my first husqvarna.

Have you ever tried to mate to pieces of metal together with out any sealing material any where else besides a husky head?
It never seals does it... How can you believe that its a perfect seal with out any sealing agent. I know there is no gasket and you lap the two together but I would also find it hard to believe that there is no leaky heads out of all the bikes out there. Did the factory allow a certain amount of leakage you have to wonder? I wonder if the factory did a leak down test after they built every engine?
Makes you think how many are out there leaking. I did here a husky mechanic who owned a shop back in the day and said they use to take a small paint brush and paint a thin layer of paint on the mating surfaces to help seal them together. Any body else ever here such?

no but it has to be FLAT and SMOOTH never found any evidence of leakage

nope, think of it like a flare fitting on a hydraulic line, metal to metal with no goop...will withstand hundreds of psi. what about a copper head gasket? no goo there...the swede engineers were no dummies. i would be very hesitant to use anything on an air cooled head to help it seal, i think this would help it leak.

I leak tested every assembled husqvarna engine and no leaks. It's a lapped fit.
I have disassembled engines prior that had leaking heads not that bad were they burned a groove but carbon in the lapped seal area.
This taught me to lap every head to the cylinder on the refresh. Maybe a little leakage can happen if there not torqued correctly. Or maybe over torqued.

Wow some history and experience in this thread on lapping of huskies. Thanks Guys. two seal lines around the entire head.

Wow some history and experience in this thread on lapping of huskies. Thanks Guys. two seal lines around the entire head.

The surface of the lapped area, should be a light gray sand blasted color. The COLOR should be even all the way round the head and cylinder. If not sure lap it one more time.
There is course and fine valve lapping compound I prefer the fine.

Assemble the head to cylinder squeaky clean.

IT is a pretty common method for sealing 2 stroke heads, my Starmakers, Stormers, Bultaco and Montesas are all the same

starmaker??? i need pixs on that one

IRC a Villiers engine of around 250cc sold as a competition engine, to be used in a frame of your choice. Looked similar to the later Fluff Brown AJS motors

Beetle's and the air cooled Citroens also had heads lapped into place with no gaskets as well