850 Case Mods

Yorkie · Dec 31, 2018

quick question - I am replacing the main on my Mk2a 850 and wondered if there were any case modifications that I should make while the halves are apart. I see there is a modification for the 750 combats but as my cases are slightly different do I need to drill the holes like DynoDave suggests for the earlier bikes? Thanks

cjandme · Dec 31, 2018

Nope not necessary. Mk2a's good to go.

Fast Eddie · Dec 31, 2018

Unless you wanna fit a reed valve breather along the lines of Comnoz’s advice, it’s an ideal time to plug the timing chest and drill a lower oil return hole...

SteveA · Dec 31, 2018

That may depend what you are trying to achieve? A reed valve breather on the rear of the case for example would benefit from blanked holes! And you can lower the amount of oil held in the timing cover if that is important to you!

Do you need to do either of these? Well no.

Fast Eddie · Dec 31, 2018

Quite right Steve, no he doesn’t need a Comnoz style breather... but if he wants one, now is an ideal opportunity to do the necessary mods. That’s all.

Yorkie · Dec 31, 2018

I was actually planning on fitting one of Jim’s breathers. Are the mods on Jim’s site?

swooshdave · Dec 31, 2018

Yorkie said:
I was actually planning on fitting one of Jim’s breathers. Are the mods on Jim’s site?

I've seen them on the forum. @comnoz

Yorkie · Dec 31, 2018

Found it. Thanks

concours · Dec 31, 2018

I LIKE the idea of lots oil in my timing chest, lubing chain, gears, bushes, etc.

JMWO

Time Warp · Jan 2, 2019

Yorkie said:
I was actually planning on fitting one of Jim’s breathers. Are the mods on Jim’s site?

That would be the one in the underside of the engine case no doubt, being a Mk2a and you elect to go that route you might want to check the clearance for the pick up tube.
The tube would not fit in my case so milled a relief for it, shortening the tube excessively is probably not the best method if that interference is found.
It seems some 850 cases have that excess material so worth checking if the engine is apart.

kommando · Jan 2, 2019

Jim does a version with a tube that leans and clears the ledge, the bottom of the tube is belled out so it leans over but rotates as you screw the breather body in.

Time Warp · Jan 2, 2019

Not on my engine case John, I couldn't find the picture, the tube was at full lean and binding on the breather body and engine case with quite some distance to seated (breather to case including ring seal/gasket)
Both of my breathers are the early version but point taken, perhaps not a worry with the newer version you mention.

CanukNortonNut · Jan 3, 2019

Fast Eddie said:
Unless you wanna fit a reed valve breather along the lines of Comnoz’s advice, it’s an ideal time to plug the timing chest and drill a lower oil return hole...

+1 Done this mod and couldn't be happier.
Cheers,
Thomas

850 Case Mods

Yorkie

cjandme

Fast Eddie

SteveA

Fast Eddie

Yorkie

swooshdave

Yorkie

concours

Time Warp

.......back to the 70's.

kommando

Time Warp

.......back to the 70's.

CanukNortonNut

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