Crankcase mods - advice please

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Nigeldtr

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Jul 26, 2012
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Hi,

I am just putting the bottom ends back together for a 70, 750 Roadster and a 93, 850 Mk IIa. I have seen recommendations to put in an oil drain hole down bottom left of the oil pump to stop the timing cover filling up with oil - would appreciate any views or experience. The 750 will also get the breather holes in the timing side crankcase and the breather moved to the Mag hole blanking plate.

I have also seen a lot about breather volume, pressure frequencies in the timing cover etc etc and was just wondering why not just leave out the "sealing washer timing side bearing" (NMT 2008) as this would let the oil fall and allow more air to flow around trough the bearing (appropriate "smaller" diameter washer replacement being used)?

Merry Chrsitmas and Happy New Year to you all!

Regards
 
You don't want to leave the washer out. The bearing could be flooded with oil from the timing chest which will cause the bearing to fail at high speeds. Jim
 
If you move the breather to the timing cover the additional holes in the crankcase are needed. I did this mod to my '72 and don't recommend it as it did not make an improvement. Goes back to if it isn't broken don't fix it. Your choice, though.
 
I assume the 70 roadster has the timed breather at the end of the cam? Leaving it and adding a breather at the mag boss may be the ticket. If one is good shouldn't 2 be better? I have run 2 on my 72. One at the mag boss after doing the mod, and one on the lower left (original). I have experienced no ill effect form the added breathing and noboby has commented negatively when mentioned here. I see this as a good omen for sure.

I believe the timing chest needs some oil to pool and there is a return hole to maintain a certain level. I believe it is just above the pump, adjacent to the left. The sealing washer does not seal completely and allows a certain amount of oil to bathe the bearing.

Crankcase mods - advice please
 
pete.v said:
I assume the 70 roadster has the timed breather at the end of the cam? Leaving it and adding a breather at the mag boss may be the ticket. If one is good shouldn't 2 be better? I have run 2 on my 72. One at the mag boss after doing the mod, and one on the lower left (original). I have experienced no ill effect form the added breathing and noboby has commented negatively when mentioned here. I see this as a good omen for sure.

I believe the timing chest needs some oil to pool and there is a return hole to maintain a certain level. I believe it is just above the pump, adjacent to the left. The sealing washer does not seal completely and allows a certain amount of oil to bathe the bearing.

Crankcase mods - advice please
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That drainback hole is in a good position for a vertical motor like it was designed for. When you tilt the engine forward like a Commando then you end up with excess oil staying in the timing chest. Jim
 
comnoz said:
[
That drainback hole is in a good position for a vertical motor like it was designed for. When you tilt the engine forward like a Commando then you end up with excess oil staying in the timing chest. Jim
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You're kinda leaving this open to conjecture. This is a 72 case shown above. As far as I can tell, other than the Atlas being vertical and not have this hole, all the Commandos from then on have this drain back hole. It really begs the question, if the verticals didn't have it and all the canted ones do, as shown in Dyno Dave's crankcase evolution, then what's the deal.

I know you are not one to split hairs, but how much oil is too much in the timing chest and what, if any, is the bad news in this canting issue.
 
Here is why I advise moving the oil return hole.

This is a old "88" case. The tape shows the oil level. Atlas cases were similar.

Crankcase mods - advice please


Here is a Commando case. The oil hole is pretty close to the same position as the "88" The tape shows the oil level.

Crankcase mods - advice please


If you had a sight glass on your oil tank you would see just under a quart of oil is hanging out in the engine when you are driving down the highway. I have installed a window in a timing chest to see for myself. It is full of oil being churned by the timing gears. Little if any oil gets by the rotating seal washer. It is there to make sure oil does not get into the bearing. Rolling element bearings will hydroplane and fail with excess oil.

Here is the oil level with the new hole drilled. There is plenty of oil to contact the crank pinion and get thoroughly spread around for lube. I have watched through my window to see it. This mod has been made to 100's of bikes with no problems. With less oil trapped in the timing chest the oil temp stays lower and the points seal is not so prone to leak. Conjecture no -just finishing the job Norton should have done when they started building Commandos with Atlas motors. Jim

Crankcase mods - advice please
 
Thanks for the replies. seems to make sense to have the lower drain hole, can't really understand why it was designed to be so high - another mystery. On the one hand, I am tempted to just leave it with the camshaft breather but as I have the cases on the bench, I may as well drill the extra holes, any harm in having two breathers?
 
OK, please excuse me while I split hairs here just a bit
I see your point but I feel your examples are a little drastic.

Here is mine with the drain back hole below the spindle.
Crankcase mods - advice please


And yours, above the spindle.
Crankcase mods - advice please


Mine will have a conciderably less amount of oil than yours without the add hole below the pump.

I agree with your finding and withdraw any conjecture. Now, will you agree that it isn't as bad as you demonstrate?
I love this shit! :)
 
Just a thought, does the large bearing washer act as a sort of oil flow restrictor for oil feed for the timing side main which also relies on the timing side being full of oil? Obviously doesn't apply for the drive side.
 
pete.v said:
OK, please excuse me while I split hairs here just a bit
I see your point but I feel your examples are a little drastic.

Here is mine with the drain back hole below the spindle.
Crankcase mods - advice please


And yours, above the spindle.
Crankcase mods - advice please


Mine will have a conciderably less amount of oil than yours without the add hole below the pump.

I agree with your finding and withdraw any conjecture. Now, will you agree that it isn't as bad as you demonstrate?
I love this shit! :)
Click to expand...

Yes, in the later years Norton must have realized there was a problem and they added another hole to aid drainback and did away with the hole near the rear of the case. But from what I have found it still is not low enough.

On my racebikes I used to drill a large raduised hole clear at the bottom under the crankshaft to get all the oil out that I could. I still never had cam bushing or idler problems. Needless to say they did see limited millage and l wouldn't recommend this for a streetbike.

Crankcase mods - advice please
 
The oil return hole in the vertical Atlas case is a problem. Its even higher than on the Commando. It can be lower about 1/2" same as on the Commando. But if it was down low by the oil pump the level might be to low for the gear on the crank shaft and oil might not circulate to the chains etc.

Any suggestions?
 
jseng1 said:
The oil return hole in the vertical Atlas case is a problem. Its even higher than on the Commando. It can be lower about 1/2" same as on the Commando. But if it was down low by the oil pump the level might be to low for the gear on the crank shaft and oil might not circulate to the chains etc.

Any suggestions?
Click to expand...

Well I have modified a few vertical mount competition engines with the same low hole as I use on the Commando. They seem to be doing fine.

I guess if I were doing a street bike with a vertical engine I might drill the hole to 5/16 and then install a piece of curved 5/16 tubing to raise the oil level enough to insure contact with the pinion gear. Jim
 
Jim,
Are there any pics on forum showing what holes to plug and where to drill the lower drain hole in timing side?
 
Beach said:
Jim,
Are there any pics on forum showing what holes to plug and where to drill the lower drain hole in timing side?
Click to expand...

Crankcase mods - advice please


Some cases have less holes to plug.
Of coarse you don't need to plug the hole for the ignition wiring.
You would not plug any holes unless you are using a crankcase reed breather. Just drill the lower drain hole. Jim
 
Drifing off to sleep thinking on our crhonic winter oil threads, it occurred to me that a tiny additional very low oil drain should/could be added that will drain cam case after shut down for more oil changed per change but not limit the actual running level set by larger hole. I want my Peel to wet sump to some extent for cam splash oiling on first kick over. Peel has fail safe non electric anything valve to prevent tank oil wet sump.
 
hobot said:
Drifing off to sleep thinking on our crhonic winter oil threads, it occurred to me that a tiny additional very low oil drain should/could be added that will drain cam case after shut down for more oil changed per change but not limit the actual running level set by larger hole. I want my Peel to wet sump to some extent for cam splash oiling on first kick over. Peel has fail safe non electric anything valve to prevent tank oil wet sump.
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Maybe, but it might be quite a while before the timing chest was refilled after each start if your intake rocker arms are snug on the pivots.
 
My meager knowledge of plain face gears and chain links is they don't need much if any lube for time enough to get oily enough again by time engine warm enough to give'r gun. Only benefit of tiny drain would be 1/3 cup more oil changed on draining to change oil. Both my Combats throw oil out the exhaust rockers on clock faces and past tire soon as oil pressure hits with blips over idle. Anyway appreciate the awareness of the mod and its slight benefits of oil heating drag elimination. On some bikes the oil pick up gets uncovered on wheelies so can't hold long or siezes up to discover the issue in the first place. Cdo's are safe to hold wheelies and feed oil in but may wet sump some till full enough to reach sump drain. Not a common concern here of course.
 
hobot said:
On some bikes the oil pick up gets uncovered on wheelies so can't hold long or siezes up to discover the issue in the first place. Cdo's are safe to hold wheelies and feed oil in but may wet sump some till full enough to reach sump drain. Not a common concern here of course.
Click to expand...
Not, if during your modding, you have blocked the forward pickup and opened the rear as suggested.
 
On some bikes the oil flow to pump feed gets uncovered which can't happen to C'do's with factory oil tank even if nose low on steeps or stoppies. Draining back out might wet sump some but so what compared to starving big ends. Comnoz has done a stoppie with his loaded full fairing. I will have to see how much oil TS case retains then see how much sump oil needed for cam sling and make decision on what TS level to drill for plus tiny drain to get some wet sump start sling.
 
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