Hi. Rebuilding a 1960 Dommie 99 engine.
I think I read somewhere that the gap between the timing cover and crankcase before the cover is screwed tightly against the crankcase should be 10 thou to allow the cover to compress onto the rubber oil pump nipple.
With my cover pushed onto the engine, I have zero gap at the top of the cover and 60 thou at the bottom. If I remove the rubber nipple from the oil pump spigot, the gap at the bottom is 17 thou. I can’t get the bottom of the cover to close up against the crankcase unless I use the cover screws to pull it into place.
I also removed the crankshaft oil seal in case that was causing a problem, and removed the oil pump rubber nipple but there was still a 17 thou gap.
The cover is flat (1.5 thou difference between top and bottom) and it doesn’t look like it’s been skimmed.
Should I be worried about this large gap?
The paper timing cover gasket is only 10 thou thick so I’ll still have a 50 thou gap to close down with the screws.
Any advice gratefully accepted.
Regards
Tony
Are the dowel holes
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Oil Pump Mounting
Check the Oil Pump Mounting. Are the nuts too large and touching the inside of the cover
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George and Philip, top marks…
George and Philip, top marks to both of you! I had a really careful look at the inside of the cover and there was a very sharp vertical line in the bottom right-hand corner. That line wasn’t very easy to spot as the inside of the cover has been aqua blasted. It coincided with the outer corner of one of the oil pump nuts (well done Philip). I didn’t have any reduced diameter nuts so I used ‘standard’ size. I got the Dremel out and shaved a very small amount from the cover and it now mates and closes properly with the crankcase - BUT that’s without the rubber oil pump nipple in place. When I fit the oil pump nipple, I’ve still got a 1.7mm gap at the bottom of the cover - that’s also the thickness of the nipple. However, I can pull the cover fully closed with the cover screws and the crankshaft rotates fine. I therefore think that it’s probably all ok now - unless anyone has a different view on this.
Thanks again for your help.
Regards
Tony
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Intermediate Gear Spindle.
I would not advise using the cover screws to pull this in to get a better seal. The thicker Commando cover gasket ( 25 thou versus 8 ) would help but there appears to be another issue worth looking for.
There were several versions of the Intermediate Gear Spindle for the Norton Twins. Some had a single scroll others a double. I once rebuilt an engine with a timing cover which also would not sit flush. It turned out to be the gear spindle was too long. It was missing the chamfer needed at the slotted end and hence not sitting far enough inside the cover recess.
The attached photos show the naughty spindle next to a good one. Checkout the ends.
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Thanks Philip. My spindle is…
Thanks Philip. My spindle is a single scroll type but I don’t remember seeing much of a chamfer on the end that goes into the cover - I’ll have a look tomorrow. That would certainly explain the cover being held off by ‘something’.
Regards
Tony
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In the cover totally clear? Off chance that a previous owner used silicon sealant and a blob is sitting at the bottom of one of the dowel holes? Worth removing lower dowel and trying cover without it to see if it fits ok?
Is there any indication of where/if it is ròcking on something? If it will screw down I would have thought whatever was holding it off would leave a witness mark .
If you screw it 'home' , does the crank still rotate ok without any unexpected noises?
Please let us have an update on what you find.
George.