I was referred here for assistance in sorting out a current build of a KM21/M20 engine, for a one-off special.
What I have is a set of KM21 cases, part number 66-1602 and 66-1604. Although my spares catalog lists them as different
part numbers for 1939 than what I show stamped internally. Anyway...
Through research I thought I had found a proper crank/conrod from an M20 that would interchange with my KM cases,
and I could easily build up an M20 off of this platform. WM parts seem to be readily available in comparison to the early M21 pistons,etc.
I bought what turned out to be a set of 66-635 flywheels, and a nice tight 68-481 conrod attached from a '43 WM20 that was broken down.
By the numbers this appears to be a later M20/M21/B21/B33 set of flywheels. ??? Not sure on this fact. I checked the spares catalog, and the M20/M21 shared almost all of the same part numbers on the output shafts and flywheels, other than material at times between steel and iron...
So, I assumed an easy marriage of the M20/M21 could occur.
I did a test fit upon the crankshafts arrival, but to no avail. The cases lacked closing by about 1/4".
The cases had old races in them, and the crank came with its own roller bearings intact, so my first instinct was perhaps
a mismatch of particular roller bearing manufactures was the fault. I pulled away one side roller bearing hoping for closure.
Same result. I tried the opposite side, with the same result. I then thought perhaps the roller to ball spacing collar that came with the
crank set was incorrect, and removed it. Still the same result. With only the outer ball bearings installed...still the cases lack closing.
It appears the shaft shoulder lengths are perhaps different from the appropriate crankshaft.
I'm researching trying to see if this is a easily sorted conflict, or do I need to source other parts to make this work.
I see that the flywheels should be 66-636 drive side, and 66-634 timing side. Although the engine shafts from M20 and M21
are listed as the same 66-644 and 66-640 in my spares book for 1939.
A) I could buy a set of M20 cases and solve it simply, but I like the pre-war aspect of the KM21.
B) I could seek out an M21 crankshaft assembly.($$$)
C) I could modify my current set-up, if I had the proper measurements.
D) I have something else going on here unforseen, causing my issue.
Anyone have any light to shed on this subject??
I've been building A's and B's for a while, and decided I needed an M in the stable.
Im just not knowedgable yet in these particulars.
Thanks in advance!!!
email (option): skywalker1971@msn.com
Hi Luke. I'm sure Ian Wright will be along later as he is far more familiar with the different models and periods of change. But many of us have fitted an M21 crankshaft into our M20 crankcases and I'm not aware that the KM cases are different. Previous cases (1937 or 38??) were narrower with only one bearing on the timing side.....But that wont affect you.
Presumably your outer drive side main bearing is all the way in, past the circlip groove? You should be able to fit each case half in turn to see which side is not meeting the middle of the conrod.
Regarding the numbers that are cast into parts. (like the conrod which is one digit out from the parts list) These are the foundry numbers before any machining or assembly after which the part number becomes that in the lists. Ron
email (option): ronpier@talk21.com
At first glance I thought I had an early style HM from 37/38 that was perhaps a leftover in '39.
after inspecting the differences I ruled that out right away. I thought, just my luck. LOL
I'm going to check some precise measurements this weekend.
And look for burrs or wear on a shaft that may be hanging me up.
I will check the race fitment, as you suggested too.
Thank you.
We shall see if there is a mechanical issue, over a parts issue.
Perhaps more will elude to my difficulty.
-Luke
email (option): skywalker1971@msn.com
Hi,
Did you check if you have a matching set of enginecasings? They should be stamped with the same number on the side facing the front frame tube.
Non matching engine casings can have a very poor fit.
Regards,
Bastiaan
email (option): wdmotorcycles@gmail.com
Yes, I did check that also.
Both sides stamped #3262, and unmolested.
Good call though!
Thank you.
I think I may have found the issue...
The outer most drive-side bearing is kind of gnarly on the inside diameter.
I flipped the case around and that bearing will not go on the appropriate shaft.
Tomorrow I will drive out the roller bearing race, and ball bearing and get a closer look.
The retainer clip was missing as well, but the bearing seemed to be seated correctly with the thin shim behind it.
I ll keep everyone posted.
Thanks.
email (option): skywalker1971@msn.com
Those bearing circlips are a nightmare so I bought the type with the little loops on each end. My bearing supplier managed to find some with the correct thickness which I think were from USA.
Here is some info from the technical page http://www.wdbsa.nl/main_bearing_circlip.htm
Ron
email (option): ronpier@talk21.com
Thanks, I will for sure convert to a conventional eared snap ring. Thanks!
Sound advice.
AFAIK the only difference between early & late cases was the strengthening plate for the cams
And the placement
Early cases had the cams closer together and the cases end to crack around them'
Am yet to see a clean one
They cured this by widening the space between the cams wih a bigger pinion and of course he carrier plate.
Not sure when they did it
The M23 is the early narrow case .
email (option): bsansw1@tpg.com.au
Good information to know.
Thank you.