I have a feeling that's a threaded ring in the outside ?.
ET: Engine (Twin) Chopped Cases
- Thread starter D.Harvey
- Start date
From the pictures I would assume he ran a single row primary and a Norton gearbox. A belt drive primary is the way to go, I've had one on mine for 25 years with a Norton box, Commando clutch and crank mounted alternator, which can be done with a standard mainshaft with a bit of ingenuity (I can tell you how) the only problem was oil coming down the g/box shaft making the clutch grabby. I now have a top run guard on.
Hi Chris,
Did you need an ESA or some kind of cush drive set up with the belt drive primary, or is this taken care of by the belt itself? Thanks.
Which is one of the ideas I had planned to do.
Had yours been taken down around the bearing housing Chris?
You have 2 large bearings next to each other, Drive side,
I would think that is strong enough, A lot of engines have far less,
Maybe only use 8 to 1 pistons ?, I am still on 9 to 1 s, Not had any pinking, But a lot of us have lowered the Ign' timing a nats,
Both of which is a good idea with this rubbish petrol we have now.
You could sell the cases on, There have been a few people looking for chopped cases,
They are hard to find.
In reply to your two questions, I have no cush drive in the system at all, the back wheel is a Manx copy, it doesn't seem to bother anything.
I didn't take anything away around the bearing housing, just took what was left of the primary casing wall back, leaving enough to be able to drill and tap for the alternator mounting, it was cut well back already, basically needed milling flat to clean it up. I actually had some welded on where it tapers away at the back/top as it was cut even further in.
The person who rebuilt the bottom end used a sealed outer bearing with the inner seal removed, I think this was wrong and the seal should have been left as after a while it started leaking (I now have an external seal) on my Triumph I have just the fully sealed bearing and that has been no trouble.
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Chris, looking at your picture, the clutch diaphragm looks unusual having an extra ring around the centre. What's the story?
Sorry Bill, no idea, it was like that when I got it (2nd hand from some autojumble no doubt)
The belt will not provide any significant damping. If that were true, modern cars that use these belts for timing belts would have variable timing, which is not the case. The saving grace of these systems is that usually the clutch is far superior to older clutches and will work admirably under very tough conditions. The ESA does most of its work when starting from a stop, which is not what race bikes are required to do during races.
I think the decision comes down to deciding if you can trust this compromised bearing journal to be as reliable as a stock one. Otherwise, you will spend tens of thousands of Pounds building a Lightning with a risky mechanical problem. If you had posed the question as one of "I have to run a 1/8" wide drive bearing because I don't have room for a stock one..." I suspect the eagerness to build an expensive bike around this problem would diminish. The fact that it is difficult to measure the damage done is not a good reason to ignore the problem.
That being said, I think the journal could be repaired. It will take some skill, but it is worth discussing. If the journal can be strengthened, you could install a clutch with a cush drive, or a rear hub with a cush drive, and that would allow you to use a belt or chain with good results. If you have concerns about locating the crankshaft, you might consider running a ball-bearing conversion for the main, which tends to prevent the crank from moving. You will have one circlip, and the nut on the end of the main to help keep the crank in place.
David
Not when I was selling my set Bill - all prepped (by Bob Dunn) and ready to go - they went for a song!