Hi,

I'm beginning the bottom end rebuild on my M21 & I'm wondering about the shim between the drive side crank case & the outer drive side main bearing. When I stripped the engine there wasn't one present. The service sheet (607 i think) says that a new washer will be required & in a parts drawing I have it's shown as 66-661 'engine bearing shim (drive side)'. Does anyone know what thickness this should be? The service sheet also says that the conrod only needs to be visibly centred in the crankcase mouth so I guess it's not that critical? Will the thickness of this shim depend on wear on the bearing spacer or some other factor? I've looked on Draganfly's website & can't see it listed for sale.

Many thanks

Ben

email (option): mad_king_soup@hotmail.com

Hi Ben...The crank is located in position against the inner face of the outer drive side main bearing which is in a fixed position in the crankcase. Behind this bearing but still within the crankcase is a small oil baffle plate. This fits into the recess machined into the cases behind the bearing.
Crank position within the cases is governed by the main bearing spacer, which should be 1.000" to 1.005" long,the width of the inner roller bearing and the oil flinger plate...all of which are pulled up against the 'fixed' outer bearing and the flywheel 'cheek' when the engine shock absorber is tightened.
Shims can be fitted behind the sleeve that carries the engine sprocket to adjust the alignment of the engine sprocket and the clutch sprocket.
I have also seen shims fitted against the main bearing spacer to take up the wear on that component...Personally I don't think that is a good idea as there is a 'fretting' action against the spacer, caused I believe when the engine shock absorber operates, and this could break up any shims fitted..Conrod centrallity is not really that critical..there is plenty of space within the pistons gudgeon pin bosses to accomodate some misalignment of the rod. Correct crank positioning is more important in relation to the correct meshing of the oil pump drive gears...Ian

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

Original shim was 0.008" to 0.010" thick.
Original purpose was part of the "sealing" of the outer main bearing. Effectively a "labrynth" seal, which was not very effective.
Omitting the shim will affect primary chain alignment, but not "fit" of main bearings.
Absolutely essential that spacer between main bearings is within spec, see tech section, 1.000" min.
Fit a sealed ballrace as outer bearing.
See tech section.

email (option): n.gentner@bigpond.com

Hi Ian,

Thanks for that! I see the recess you mentioned, I'm fitting a sealed outer bearing (with the inner seal removed) so it sounds like I can ignore this washer if its just an oil baffle & not a shim. Would you recommend filling the oil drains between the bearings & drilling at the top as shown in the technical section of this site?

Thanks again,

Ben

email (option): mad_king_soup@hotmail.com

Also important is that the flywheel shoulder or cheek is undamaged and flat and the same for the oil flinger plate where it sits against it..Note Neales comment..if you leave out that oil baffle you will affect the engine sprocket/clutch sprocket alignment by that amount...Personally I don't make any alteration to the oiling..it works OK in its standard format and these engines don't have any main bearing issues..even in a highly tuned OHV specification..and I've tuned them to over 40BHP at the crank.Ian

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

Hi Neale,

Thanks, I see what you mean about primary chain alignment. I suppose 0.010" would not have a discernible effect. I'm going to fit a sealed bearing as you say and I'll also fit a new spacer as the original was well under 1"

Thanks for the info

Ben

email (option): mad_king_soup@hotmail.com

when does thick become long

email (option): roger.beck@node6.com