I don't think they have to be dead square ?, Now where did I put those small bearings ??. Cheers Bill.
E: Engine Big End Replacement
- Thread starter Cyborg
- Start date
Hi P0
I haven't worked on many M/C big end ass'ys and when i did it was as a teenager in the early 60s and then only on singles, but my methodology - fwiw - was to first bump the ass'y on to a solid block of wood placed on the workshop floor to get the alignment as close as is possible just by using a rule across the od's of the flywheels, starting adjacent to the big end ass'y then at 90 degree intervals. Checking the 'parallelness' of the flywheels with a vernier. If the f'wheels are parallel then it is possible to get the ass'y close to truth just using the rule method alone, before finishing the job between rollers as per V B's jig.
Have to say however, that the further away the DTI is positioned from the bearings the better. In fact, to facilitate this, i would go so far as to say that it may pay to make up sleeves that fit over the keyed/splined portion of the mainshafts. If you really want to go the extra mile then insert one main shaft in a crank case and then secure it onto a solid bench or, preferably, a mill bed and check the truth of the alignment with a DTi running on the other mainshaft. In essence all the misalignment transfered to the one shaft. It is quite faff and is a bit ott but can be quite an eye opener because any runout is magnified.
HTHs
Roger
So if the combined total runout (sum of both shafts) with the crankpin nuts torqued is within .002 either way I measure it (between centres or on rollers) can I call it a day?..... never mind, I can't bring myself to hit it again..... so I'm done until I start weighing whatever piston I'm going to use. Couldn't find a suitable stump, so made a crank holder on the bench and held a lead ingot between the flywheel the the large hammer. Holder also worked for torquing the crankpin nuts.
Good enough for me, Now you have all the gear, You can do mine !.
Had to go for a ride on the L/ning, To remind myself why I am doing this, And to see if I can still ride !.
Cheers Bill.
dont go more as 0,03mm runout, if not your main bearings will work loose, in a vinnie its not the bearing fit which is at fault, but the fact that 4 bearings needs to be inline, and a strait crank. if not something has to give.... i consider it even to much, and will take the odd day extra, to hit it hard
or use C3 ++++++ bearings, and rattle along
or use C3 ++++++ bearings, and rattle along
I agree with Vincent on this. I am not sure what you mean by 'combined total runout'. Are you adding the two side's values together? Does this mean that you could have two thou on one side and zero on the other. My opinion is that two thou(0.05mm in Vincent speak) is too much. Sometimes they just wont get down to the lower values but if you think an extra thump or two will do it then go for it.
Yes, adding the two side values together. I got that from Tuning for Speed. It reads " Well the correct amount of runout is zero, but this is rarely attainable, and if the sum of the errors indicated on both shafts comes to less than .002 there is nothing much to grumble about."
It does go on to talk about 3 or 4 bearing cranks and I get that the 4 bearing will be less forgiving. There is roughly .001 per side measured with the crank on rollers and the dial gauges outboard on the shafts. Part of the runout readings I'm getting if from battle scars on the outboard portions of the shafts. If I clean them up (which I will do now that I know this crank will be used and not tossed in the dumpster) and machine collars for the gauges to run on, it would read slightly less.
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dont go more as 0,03mm runout, if not your main bearings will work loose, in a vinnie its not the bearing fit which is at fault, but the fact that 4 bearings needs to be inline, and a strait crank. if not something has to give.... i consider it even to much, and will take the odd day extra, to hit it hard
or use C3 ++++++ bearings, and rattle along
.03 mm on each shaft? or .03 mm for the sum of both shafts?
I'm not sure the bearings in cases are perfectly in line and even if they were, that alloy seems to move around like wood. I understand the need to strive for perfection, (my bride explains that to me every 3rd Thursday of the month). The C3 bearing thing is an interesting discussion. It seems like in some situations where the interference fit is less, C3 should not be used.
Anyway, I don't know if I could get this crankshaft any closer. It has suffered greatly in the past and I'm surprised that I got as close as I did.
Thanks for your input. It's appreciated.
you can take the small timing bearing out, it ll last for longer, if the crank is crooked
i put it on the big mains and than both other bearing positions may not be more than 0,02mm (aim) but if 0,03mm (after two hards days of hitting it), make the clearance on the bearings a bit bigger.
one can not add them up.
Oh and i go from it that the cases are line drilled or does one say bored?
cheers
one can not add them up.
Oh and i go from it that the cases are line drilled or does one say bored?
cheers