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Camshaft end play

Posted By: Towner

Camshaft end play - 04/01/11 11:33 am

Hi,

sadly it turns out, that the exhaust thread repair does not hold (see Post http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=364273#Post364273).
It comes out of the head more and more, so that the exhaust pipe can't be fastened anymore. So I stripped down head and barrels again and noticed, that the
new JP piston had already a seizure and has to be renewed as well. The cams look good. I measured the endplay of the camshaft. It is about 0.15" (0.4mm).

Is that still in limit ?

Regards,
Ralf

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Posted By: L.A.B.

Re: Camshaft end play - 04/01/11 3:28 pm

Originally Posted by Towner
The cams look good. I measured the endplay of the camshaft. It is about 0.15" (0.4mm)


I hope you mean 0.015" (15 thou' = .381mm)? As 0.15" is 3.81mm.

If so, then that sounds OK.

Previous JP piston thread: http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=314083
Posted By: kommando

Re: Camshaft end play - 04/01/11 3:59 pm

JP uses a low number of base castings to cover a wide range of final applications, hence for most applications they start with a large casting and machine off the required amount. Except for a few applications at the lower end of the sizes the base casting covers they are always heavier than the original piston, that together with the small batch sizes they work with which seems to result in missed machining operations means they should only be considered as a last resort. I would be looking for some Hepolites or using the Cyclecraft (if they do 850 pistons) with a good ring brand.

I also had an 850 with a bronze insert for the exhaust thread repair which came loose, I sent the head to Mick Hemmings who welded a new aluminium insert. He charged the same as for a normal repair on stripped threads but there was extra work involved.
Posted By: Towner

Re: Camshaft end play - 04/01/11 7:28 pm

Hi,

@LAB: 0,015" of course (0,40mm).

I sent head and barrels to an experienced mechanic, who will weld new aluminium inserts. He has also good experiences with GPM pistons which are sold by Andover Norton . It may be possible that he can still use the first oversize.

Ralf
Posted By: Alan Prudhomme

Re: Camshaft end play - 04/02/11 3:09 pm

Do yourself a big favor and buy some brass exhaust nuts. Alloy expands twice as much as steel which makes keeping steel nuts almost impossible to keep tight. I suspect the crack in your head was caused by the alloy not being able to shrink fully on the steel nut (possible)???
I bought chrome plated brass nuts and they loosened up like the iron ones do....think I got the brass ones from NORVIL. The brass nuts stay put so you can toss all the tab washers wire and springs. Brass expands at the same rate aluminum does.
Posted By: Towner

Re: Camshaft end play - 04/02/11 4:50 pm

Hi,

the thread repair problem very likely comes from using a steel insert.

Regards,
Ralf
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Posted By: Towner

Re: Camshaft end play - 04/09/11 5:14 pm

Originally Posted by L.A.B.
Originally Posted by Towner
The cams look good. I measured the endplay of the camshaft. It is about 0.15" (0.4mm)


I hope you mean 0.015" (15 thou' = .381mm)? As 0.15" is 3.81mm.

If so, then that sounds OK.

Previous JP piston thread: http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=314083


I am not really sure that I got the correct reading, because it is not easy to measure. So I tried it again today. May be more than 0.015" but defintety less than 0,04" (1mm). Where is the limit and can it be adjusted without splitting the cases ?

edit: I just managed it to measure it more exactly with a feeler gauge at the thrust washer. It is 0.027" (0,7mm).

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Thanks,
Ralf
Posted By: Towner

Re: Camshaft end play - 04/09/11 6:42 pm

I recognized that only one thrust washer can be seen on the timing side. But in the manual is stated that after engine number 200000 2 washer are required....

The left conical washer (06-1086) is on my camshaft:

http://www.oldbritts.com/cam_bush.html
Posted By: L.A.B.

Re: Camshaft end play - 04/09/11 8:08 pm

Originally Posted by Towner
I recognized that only one thrust washer can be seen on the timing side. But in the manual is stated that after engine number 200000 2 washer are required....


My factory manual copy gives the following information:

"On engines between numbers 200000 and 300000, a flat thrust washer is fitted between this chamfered washer and the crankcase."

As your Commando is a 1973 850 model, it should have an engine number higher than 300000? So, no second washer.

Also, check what it says in the Old Britts info:

"06-2601 -- NORTON, Washer, Thrust, Camshaft, Some 1972( $5.62 each). This tabbed thrust washer is only used when fitting the 06-2600 bushing and there is a locating hole for the tab in the crank case."
Posted By: Towner

Re: Camshaft end play - 04/10/11 7:44 am

Yes, my Commndo has number 312091. So one washer is right. Thanks for the information. In my manual and also in the Haynes they only talk about later than 200000.

I found this post from Dave Comeau which confirms my reading of 0.030". In this post they also say, that the tabbed washers should be avoided.
http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=69240#Post69240

Originally Posted by Dave Comeau

..... and the cases and thrust washers are normally 1.105" total giving .030" end float/clearance.


Regards,
Ralf
Posted By: Towner

Re: Camshaft end play - 05/15/11 10:53 am

Hi,

the parts are back and my Commando is ready again. I also mounted new exhaust pipes and lock rings. The reason for the piston seizure were not the JP pistons but a wrong clearance of only 0.0035" (0.09mm ).

Ralf

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