H6 gearbox and crank clearances

[farmer58za]

Hi All
I'm re-assembling the bottom end of my H6, which will be made up with components from two different motors. I just need to confirm the clearances:

Mainshaft, countershaft and shift drum clearance = 0.1-0.2mm (from Clymer manual)

I can't see what the specifed crank clearance is but I have measured up both the cases and they give nearly identical results (including gasket and shims) of 1.25 to 1.3mm clearance to the crank.

Seal holder gaskets are 0.4mm and centre gasket is 0.7mm.

Are those OK?
Regards
David

[Montynut]

I read your post as meaning how do you adjust or set up the crankshaft in the crankcases?

There should be large shims between the crank seal carriers and the main bearings which centralise the crank in the cases. I have a set of mains with a slightly reduced OD to allow them to be a slide fit in the cases to allow shimming set up. This is usually a once only set up although can change if the crank is rebuilt and not returned to the same measurement as before or if a different thickness gasket is used. In your case combining components from two engines requires a full engine set up as you are doing. The clearance should be the same as the gearbox shafts. Have a look in the parts book and you can see the shims. If this is not done the crank will float longitudinally.

If you read the gearbox setup section carefully the shift drum is always shimmed from the right (ie the shims are always added to the right of the shift drum) with only one shim on the left while the input and countershafts are centralised. This is critical to ensure that the shift forks do not have constant pressure on the selector forks. The final adjustment of the shift mechanism is done in top gear. You keep repositioning the gearbox shafts until you can shift through all gears to top gear without moving the shafts (very frustrating) then look through the detent plunger hole and adjust the shift mechanism to centralise the detent groove. It is all in the manual but not very clear I am afraid.

Hopefully Jared will post shortly as he has done hundreds of them naturally

[farmer58za]

Thanks Montynut
Thanks for the advice.
Yes, setting up the crank is a bit of a "chicken and egg"excercise as the shims go behind the bearings, which are a press fit. Fortunately, I have the shims from both motors to work with.
Regards
David

[cappra]

Hi guy's,
The shaft end clearances are all valid. As is the centering of the selector shaft. As far as crankshaft endplay, in a perfect world, loose id beaings would be fitted so precise endplay
could be determined. You can also add shims to the thrust side until; you can feel drag on the crank and remove a shim and have no drag on the crank. Make sure the rod splits the centre
case, by centering the crank halves. My experiance has shown that Montesa motors are very tolerant when it comes to endplay and tolerances. I have rebuilt motors with out of spec clearances
that were operating just fine. Running the gearbox on the table can be an exercise in frustration at best!

                                                                                                                                                                           Jared
                                                                                                                                                                           S/W Montesa

[Montynut]

I use a set of used main bearings (but still in good condition) removed from an engine which have been linished down slightly on the outer cage to allow the bearing to easily move in the cases and that allows easy shimming of the crankshaft.

[farmer58za]

State of play as at tonight:

http://s215.photobucket.com/user/farmer58za/media/IMG_0191_zpsdc0c5917.jpg.html

Regards
David