Just got my M20 engine cases back from vapor blasting, as we call it in the U.S., they are now gorgeous factory looking aluminum.

Question, I was about to assemble the engine with the workshop manual and I may be confused. On the drive side case (66-1604) it calls for a "new washer" to be installed. What is that? And does this seal the case so oil does not leak into the chain case?

What I have, described from aluminum case - inward, a large round thin flat washer, then SKP 6502A open ball bearing with attached race (made in Sweden), spring clip, spacer, bearing race MRJA25 (made in England) and finally answered open roller bearing MRJA25. None of the bearings are "sealed". Is all of this correct for assembly or do I need oil seals in there or something? And if I missing something please let me know where to buy it! These were all in the engine when I took it apart.
Thanks!

email (option): questmasters(at)hotmail(dot)com

Your order of assembly is correct and the spacer should not be less than one inch long. The outer ball bearings were open and hence the need for the oil retaining washer.

I've just fitted a new set of main bearings, supplied by Darren Wrudd from this site and the outer bearings came with seals, so I flicked the inward seal out to allow for normal oil feed.

You can inspect the inner roller bearings for pits to the outer races but difficult to measure wear to the race or rollers. The outer bearings of course are more difficult to inspect. Ron

email (option): ronpier@talk21.com

You should also have an oil flinger plate that goes against the flywheel face before the drive side bearing inner is fitted to the crank...Ensure the flinger plate surface where it contacts the crank and bearing inner is flat and unworn...

It's best to replace the original clip that retains the 6205 bearing with a modern version that has holes for circlip pliers...Far easier to fit and remove when required...Ian

email (option): ian@wright52.plus.com

And just a heads up on what Ian said about the circlip. The original circlip which is a bugger to remove and refit is about 1.7mm thick. A standard circlip is about 2mm thick, but my local bearing firm got me some at 1.6mm thick which are of US origin. So easy to use! Ron

email (option): ronpier@talk21.com

Thank you so much!
Is the round flat washer completely flat? I just want to make sure because it really doesn't look like it does anything but sit against the engine case between the bearing. Meaning, it doesn't seem like a good seal.

email (option): questmasters(at)hotmail(dot)com

I think the steel washer #109 should be flat. The one I took from the bike that I'm working on was a bit dished. I expct from the clamping effect of cush drive spline #56. It acts as an oil shield and won't matter if it's slightely dished towards the bearing.....Or hammer it flat.

Regarding spline #56. There are two types. One has a reduced collar machined on which buts up to that washer/bearing to space the spline off the crankcase. The other type has a seperate ring/spacer. Which I have seen eliminated by mistake on a rebuilt engine and the guy wondered why his engine woudn't turn over. Ron

email (option): ronpier@talk21.com

Not sure if it is a good idea to use a sealed bearing for the engine outer ball bearing. Also wonder if the outer seal is not blown out by the crankcase pressure if the inner is removed.

Since reading Trevor his remarks on the breathing of the engine in combination with open bearings I stick to the original design. Any thoughts?

Regarding the seal in the bearing being blown out, I have never known this to happen, and have been supplying these sealed bearings for many bikes over the last three and a half decades :-)
Not to say that it could not, but I can't see why it would.

The practice of leaving the outer seal in the bearing is mainly to help keep the oil in the engines, I know it is sealed also but I have seen shafts slightly worn under the oil seal lip offer a dripping oil seal leak, so anything that can be done to help keep an engine oil tight is good in my experience. Lubrication is not altered really from original specs as oil still enters the bearing and drains back out.

On one or two designs that I have seen, ( one was a modern motocross bike, can't remember the other one) there is an oil way hole behind the bearing to drain the oil back but even these have run perfectly well and sealed better with the single sealed bearing as the oil just drains back from the open side of the bearing itself.

I know I am no expert on the M20 engine, but I have sold a lot of these bearings over the years and cannot see any issue with using the sealed ones. If anyone knows different, then please do let me know as one is never too old to listen and learn.

On the other hand, if you are more content to take out both seals or just use an open bearing, that's fine too, it is after all what was designed into it.
I shall be rebuilding my own though in summer, and I will use a sealed one with the inner seal removed.
Happy days

Darren

email (option): dwrudd at lineone.net

I've fitted sealed bearings with one seal removed to numerous engines during engine rebuilds and all my own bikes are thus equipped. No problems to date. Another factor is wet sumping..Having the seal may prevent/reduce the amount of oil that gets to the chain case if an engine drops its oil after standing too long without running...

Regarding the passage of oil more generally it's just a more effective version of the tin shim originally fitted. It has no discernible affect on engine breathing that I've ever noted, even in tuned OHV engines...Ian

email (option): ian@wright52.plus.com

I fitted a sealed bearing to the drive side of my Matchless G3 after it was recomended by the guy who rebuilt my srankshaft with one of his special needle roller big ends. Apparantly it's what he always does to any engine he rebuilds. Ron

email (option): ronpier@talk21.com