ET: Engine (Twin) main bearings
- Thread starter erik
- Start date
Erik, securing the Main Bearings is a problem. A lot depends on the condition of the crankcase. If it's in good condition the correct grade of Loktite will help but it's important that the case is heated to the right temperature. Just as important is that the crankshaft is running dead true. If the crankcase is damaged then maybe you should get advice from an expert like Ernst Hegeler.
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Fitting bearings with loctite in a hot crankcase could be the reason for trouble later. The crank will run true and the cases repaired by an expert but I have seen something like securing screws to fix the bearing in situ.
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My inner main bearings have a single lip. They are fitted in the cases with the lip furthest away from the crankshaft. This is supposed to stop the outer race walking out of the cases towards the crankshaft.
I fitted the same to a friends Twin Bike years ago, And have a set for the next Bike I do.
Cheers Bill.
I´d hate to weaken the bearing housing by drilling holes there. Basically the practice of having the rollers on the inner race and outer no lips is a bit unfortunate, I found the types with rollers in the outer race, so it is easy to assemble the engine and due to the lip on the inner race plus the positioned rollers in the outer there is no way the outer race can walk into the crankpin nut. Seems to me that type of roller bearing was never develloped in the imperial system.
For the near future you could use a low strength Loctite like 243 when dropping in the race at say 100 degrees C crank case. Most bearing fit Loctites are of the strong type .For maintaining positions in oversize bearing seats when hot you could dimple the seat very lightly in 4 places and checking each dimple height with internal micrometer.
For more than one reason I decided on metric roller bearings with said lips on the inner race and rollers contained in the outer race. Sizes are i.d. 30 mm , o.d. 62 mm , so there is a chance to rectify the cases by an adapter bush down from 63,5mm to 62 mm , no weakening of the case by boring the 63,5mm for a substantial bush to restore to original imperial size. The mainshaft can be sleeved from 25,4mm to 30 mm and you get all choices for different types of modern PA 66 GF roller bearings, no ball bearing in there, all roller on the crank, details per PM . Assembling the crank into the engine case is super easy as the inner races slip into rollers with no problem at all. In the photo you may get an idea about my thinking.
Vic
For the near future you could use a low strength Loctite like 243 when dropping in the race at say 100 degrees C crank case. Most bearing fit Loctites are of the strong type .For maintaining positions in oversize bearing seats when hot you could dimple the seat very lightly in 4 places and checking each dimple height with internal micrometer.
For more than one reason I decided on metric roller bearings with said lips on the inner race and rollers contained in the outer race. Sizes are i.d. 30 mm , o.d. 62 mm , so there is a chance to rectify the cases by an adapter bush down from 63,5mm to 62 mm , no weakening of the case by boring the 63,5mm for a substantial bush to restore to original imperial size. The mainshaft can be sleeved from 25,4mm to 30 mm and you get all choices for different types of modern PA 66 GF roller bearings, no ball bearing in there, all roller on the crank, details per PM . Assembling the crank into the engine case is super easy as the inner races slip into rollers with no problem at all. In the photo you may get an idea about my thinking.
Vic
So what is the correct temp for heating cases when using Loctite? That is sort of a rhetorical question and I assume it depends on the clearance and what Loctite you are using. It reminds me of a bad experience I had when the bearing race was about 75% of the way home and the Loctite set up instantly. Spoiled my day!
A Comet should not need it, Because they are closer together, They are a much better setup. Cheers Bill.