Hi Guys
I are starting to reasemble my M20 engine. I have fitted a new bigend and all new crankshaft main bearings.
All parts are good quality ,proudly branded and came from a respected supplier. ( But as i tighten the grip my shaft won't turn ).

Crank case halfs were very clean and warmed up in an oven to help fitting the outer races. All the racers appear to be fitting correctly and the conrod is central. I suspect the new big end may have added a few thou to the asembly.

The crank and casers all slide easily together but when i tighten up the case ,the crank nips up tight. If i lossen the crank case and measure with a feeler gauge a find about 0.008 - 0.013 gap.
The spacer is 1.000, if i leave it out and tighten it up all is free.
I have not been able to find any info so on setting up the crankshaft clearance or end float.

So i'm asking for some help or info to get the clearance correct. Do the oil flingers come in different thickness's ? Do i carefuly reduce the spacer thickness ?
I have carried out Dave Plumbs suggestion for better oil to drive side bearings ( in technical info ) and there was a suggestion to discard the flinger. I'm a little nervous about this so have cept the flinger in place.
Can anyone help please?

Thanks
M20-109711

email (option): wpgarage@xtra.co.nz

Is your crank shaft trued correctly?

email (option): davmax@ntlworld.com

Are the crank case halves matched?

The crank shaft has bean assembled as per the maintenance manual and as it spins freely before thae cases are bolted tight ,i think they are true but i will recheck them.

Are the crank case half matched?, is a bloody good question. the bike was in boxes when i got it, the crankcase and barrel were assembled and the crank did turn. This thing is a basket case and who knows whats been done over the years
How can i tell if they are matched ? how do i match them if they are not?

May not be relevant to your problem if clearance is your issue but you could try putting the barrel on and tightening it down to the cases before you tighten the bolts holding the cases together fully. This can help with ensuring alignment of the cases if they are a bit sloppy.
Cheers
Pete

email (option): petercomley@web.de

Phil,

A mtached pair of crankcases were stamped with a match number on the front lugs. These were random numbers but they should match on both halves.

Regards,
Leon

email (option): leonhop3@planet.nl

Hi Phil..The crankcase halves are numbered on one of the front engine bolt bosses so you can readily check if they are a pair. However, it isn't generally problematical 'mixing' odd halves with these BSA models. The main bearing housings were machined at the same time as the crankcase register (the lip and shoulder where the two halves join), so if the register is a good fit one into the other then the bearings will be accurately aligned.
The oil flinger is necessary to keep the overall length of the crankshaft assembly correct..but check that it is flat and sitting flat onto the shoulder of the flywheel.
The correct width of the main bearing spacer is 1.000"-1.005" and this should not be altered..if there is insufficient clearance in the crankcase along the axis of the crank the problem lies elsewhere.
End float of the crank within the cases is not set..in other words, the crank is free to 'float' within the cases. End float is taken up when the crankshaft shock absorber assembly is fitted and the crank is pulled over and locked against the outer drive side main bearing by the shock absorber nut.
Before fitting the shock absorber assembly, but with the cases bolted up, the crank should have perceptible end float...
The crank should be checked first to ensure it is running within the specified limits..that is within .002" concentricity on the bearing surfaces of the mainshafts. Flywheel faces should be within .005" when clocked on the faces of the wheels...However, IF the mainshaft figure is correct there is a degree of 'flexibility' on this measurement which won't affect the operation of the crank...
When you are sure the crank is running true reassemble it into the cases..If you still have a problem then something is affecting the 'length' of the overall assembly. Check there are no burrs or damage on the crank shoulders that the bearings sit against, that the oil flinger is flat and correctly seated and that all bearings are correctly located on the shafts and in the cases.In the case of the roller bearings make sure the inners are fitted the right way round..the writing and numbers on the inner and outer bearing halves should face the same way when assembled. If all of the above is correct you should have 'end float' on the crank. If you haven't there may be a problem with the big end assembly itself..Ian

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

Thanks Dave.Hans,Pete,Ian and Leon
The half's are not matched 5742-7736 but i think they are true and quite usable. I think all bearings are correctly fitted but i will recheck them all. i am a bit worried that there is an issue with the big end.

If i need to replace it again can anyone suggest a supplier?
Thank
Phil
from Kiwi land
m20-109711

email (option): wpgarage@xtra.co.nz

Hi Phil
Whereabouts in the Land of the Long White Cloud are you? I'm in Kapiti north of Wellington and wouldnt mind having a look at your progress (you are way ahead of me with the M20!!). I'll be riding down to the Burt Munro rally in November if you are down south.
Doug W

email (option): watsond@xnet.co.nz

Hi Phil..I can supply a complete upgraded big end fitted to your conrod as a 'conrod kit' which you can then fit to the flywheels..but you will need to check the flywheel tapers before going down that route as the tapers must be OK for successful truing of the wheels..see pic...Ian

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