E: Engine Big End Replacement

Cyborg

Well Known and Active Forum User
VOC Member
My clan is from the Isle of Lewes and were worshipers of the Callanish Stones (too cheap to build a church). I have two other cranks (Norton) waiting in the wings, so with the combination of my thrifty nature and my proximity to Maughns, at least in my mind, at this point it makes sense to take a stab at it. It may all come to a crashing halt once I get out the micrometer and bore gauge.
 

timetraveller

Well Known and Active Forum User
VOC Member
Come on. Have a go at it. If I, an astronomer, can do it then anyone with a bit of engineering experience should be able to do it better than me.
 

timetraveller

Well Known and Active Forum User
VOC Member
Yes, and a decent spring balance or equivalent which is accurate to a gram or so. I have always tried to balance to Vincent's original figure for twins of 46 % but I know that some of the racing boys go for 50% or more.
 

Bill Thomas

Well Known and Active Forum User
VOC Member
Hi Bill, my crank has .002" runout on the timing side mainshaft, it could do with being a lot smoother running. Tony Maughan always reckoned .0005" max runout for a smooth engine. Cheers, Stu.
Ah the real world ! Stu, I always aim for perfection, But never get it.
The standard Vin crank is not the best in the world, People have been trying bigger pins and press fit with no nuts for years, My L/ning was so smooth when I first built it, But after it's first race, Not any more !.
If I can get .002 on my 560 Comet, I will be thrilled to bits !!.
I know you liked Bird Watching Stu, But what about Fishing !!, I asked Dear old Big Sid from USA about vibration, And he told me a trick about putting 1/4"or was it 3/16 ths, lead weights up the handle bars, He could tell a good story but I thought it's worth a try, My vibes were around the 65/ 70 mph ish and it's much better now, I think it was before you were on the Forum.
Another good trick is to drill and fit a small roller, Half in the flywheel and half in the main shaft, So the shaft can't turn. Cheers Bill.
 

litnman

Well Known and Active Forum User
VOC Member
64% on my stroker. Recommended by S&S.
ET crank 64%.JPG
 

passenger0_0

Well Known and Active Forum User
Non-VOC Member
I've done a few built-up cranks (Indian, Vincent twin etc. ....) in the past and personally wouldn't align them on centres unless these have previously been ground true to the main shafts. I used a tool room centre-grinder as you don't know how much the shaft centre has been pushed around by over zealous use of an extractor. I've also seen a drive-side main shaft that was twisted with 0.006" run out on the main bearing surface when run on centres. Mentioning this to the owner he told me several years ago he had locked up the engine at revs when the main shaft bush seized in second gear. Strange it had been vibrating a bit since then and pulled out its main bearings from the cases.

There are roller type set ups out there for truing cranks but I prefer plain knife edges located on where the main bearings are located.

All to their own I suppose. I now don't have access to specialised equipment so entrust my cranks to others.
 
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