850 MkIII ES primary drive centres

Thanks for the suggestions Simon,

I was contemplating making up eccentric bushes and as you point out, top and bottom mounts would need doing to maintain vertical alignment - I was hoping not to have to strip everything down that far .

An alternative is to bore out the chaincase seal diameter on to the correct centres and sleeve it back for the seal. The up side is I've already got it stripped down that far!

I'll go and stare at it a bit longer...

Mark

Previously wrote:

Hi Mark,

The above is clearly an engineering solution which will most likely solve the problem. However, I see that you have said that there is no play in the gearbox mountings, but have you considered the engine mounting bolts ? It may be possible to jiggle the engine back and forth to get the correct alighnment. In the past I have found that the wiring gromet weeps oil as they go rock hard after a very short time.

Cheers HT

You make a good point Hans!

I'll check that possibility before comitting to cutting any metal.

I could live with a 'weep' from the wiring gromet. In this case, when parked up after a run,I get a line of oil from the rear sprocket to the chaincase, both stands are covered and oil is working it's way up the speedo cable to dribble out over the LH headlight bracket. Not a drop leaks between runs!

Thanks

Mark

Hi Hans,

Not really bizzare, just VERY oily.

I can see the oil on the back of the chaincase (only around the clutch area) as well as everywhere else, and it's the pink ATF that I prefer to use in the case and its path rearward can be traced. Oil pools in the rear sprocket recess so I'm pretty sure its getting onto the speedo drive and through the cableup to the front - forks rebuilt last year with no leaks apparent when lifting the gaiters.

Taking the inner chaincase off shows a pool of oil in the gearbox sprocket recess, again pink.

Single MKII concentric with K&N style filter with oil tankbreather piped into the end - no oil dripping from the filter. Non return breather on crankcase exit and added a filtered, non return,inlet breather to inlet rocker cover.

Chaincase centre support stud has a nut & washer behind which means it can be adjusted easily to ensure no bending of the cases.

Good point about crank end seal - it would not necessarily contaminate the oil short term but could help oil pump out of a less than perfect seal.

That seal/gearbox relationship is still wrong! I had a go with the crankcase engine plate studs and they're a good fit with no possibility of moving the cradle there.

So I'm going to source a seal with a smaller OD (1.625 instead of 1.875), sleeve the chain case then bore it to suit in the correct position. This way I get the seal in the right placewithout trashing the inner case.

I'd rather be riding it though!

Mark

Previously wrote:

We were discussing your problem at our (Shropshire) branch meeting last night. One of our members who has a Mk3, and has some experience at wolverhampton, says that the engine plates were machined with the engine bolted in position ie as a unit and that is why the engine number should match with the number stamped on the gearbox. (and frame come to that) It's just become apparent to me when trawling through the tat on ebay that on later Commandos the engine number is stamped on the gearbox. So if at some stage in it's life yours has had a new gearbox casing, that might explain the discrepancy. The easy fix IMHO would be to file the top bolt holes until the desired adjustment is achieved and then pack the gap remaining forward of the bolt to prevent it moving forward in the slot. You could make a proper repair at a later date. It would hardly constitute a bodge as that is what the previous Mks of Commando used. 0.030" would not take five minutes a side. Having seen Simon's Mk3 gearbox, you can remove it without undoing the cradle to engine bolts, unlike the earlier Commandos.

Be aware that if you have a gap on one side of your oil seal 0.030" bigger than the other, you will only need to remove 0.015" to get it centred again.

My last tip would be to buy a new seal from a bearing / seal supplier that has recent new stock rather than seals that have been sitting around for years on a dealers shelf going hard. I learnt that one the hard way.

Thanks David,

I've just checked and the engine and gearbox numbers do not match! Engine starts 406, gearbox 334 so your diagnosis seems right.

I was aware that the bike had a new main frame during it's life (MkIIa now) so it's likely other big lumps were not originally put together in the factory!

Lining everything up with the top gearbox bolt removed so all centres are concentric shows an error in the top bolt of around 1/16" which translates to the 'missing' 30 thou at the gearbox shaft (about half way between top and bottom g/box bolts). Primary chain tension at this position looks better as well so it's out with the files.

Seal is a petty standard size and local seal supplier carries stock so I should be OK there.

Thanks to all for your input.

Mark

Update

I can now report that after re drilling (boring) the engine plates for the gearbox top mounting I've got the clutch seal to be concentric within a couple of thou. I've only done a hundred miles or so since but not a drop of oil has leaked (from this area) since. I have a slight weep from the gear lever output but that's it from the primary!

I'm hoping that that's fixed it.

The plates were adjusted in situ by making up amandrell to take a 22mm hole saw with a 9/16 diameter front end touse the gearbox top mountas a guide bush - after first moving the gearbox toput everything on centre and clamping using the bottom bolt. A dremel was used to grind the engine plate away to get clear access to the gear box top mount. The hole saw was run in a beefy mains drill at low speed with plenty of lube and the guide ensured it didn't wander or chatter.

I cut holes from both sides and made up stepped washers from stainless to take up the difference between the new holes and the9/16 bolt.

While this is not something that everyone would want to do it appears to have fixedthe problem for me.

Thanks again for your input.

Mark.