E: Engine Big end needle roller bearings

[oexing]

It is a bit amusing to read : Some like to go for short stroke engines for getting high revs and high performance. Some like to go for extra long stroke - ah - for what benefit ? I got a 1935 Horex 600 four valve single with 103.5 mm stroke, had the first ride this year on Sunday. Yeah, great thumper at some 26 or 30 hp. But I would not want to punish it for extended times, forces in the engine getting unhealthy at higher speeds. I´d think a good combination of carbs, c.r. with a modern piston and unrestricting exhaust system should provide a lot of fun on twisting roads anyway.
I did complete crank webs as well , press fit parallel pins, main shafts integral. No need to nitride I´d say, get high tensile steel and they will do. Yes, machining is a laborious job, even more the grinding of the pin bore to a decent surface roughness with intergral main shaft. But a 40 mm pin in a high tensile crankweb is an extremely rigid assembly so due to this I had to apply my press to get run out from 0.06 mm after pressing in to less than 0.02mm , no copper hammer could do - or I was no longer strong enough to swing it hard enough at my age . . .

Vic

 

[Bill Thomas]

Hi Bill, I was thinking somewhere between 100 and 105, as I have yet to source a rod that will may determine the final choice, are you using full circle flywheels? I am planning heavy press fit parallel pin in Nitrided flywheels.
Best Phil.

Just reworking standard wheels, Might not be good enough !.
I think anything over 102, Can give too much piston speed ??.
The spares company had some short rods, A few months ago ?.
Cheers Bill.

 

[timetraveller]

Vic, the reason for the hardened flywheels is not for the strength but to maintain the fit of the crank pin in the wheels if ever it is necessary to dismantle the assembly. Experience has shown that unhardened flywheels move enough when the crank pin is moved in, and then later out, that the interference fit is lost. That is a beautifully prepared set of components in your photographs. Very nice.

 

[bmetcalf]

How close can you allow the mainshaft and crankpin holes to be to each other?

 

[Martyn Goodwin]

Hello everyone, this is my first post here. I am trying to source quality KZK needle roller bearings 40 x 48 x 20 being my preferred size for big end use. INA were my first port of call as I knew they did this size, it seems no longer alas. In fact my bearing supplier has come up with nothing. Has anyone here any words of wisdom on the subject. I am in the drawing phase of planning a long stroke crank for a Comet special.
Thanks Phil.

Contact Terry Prince. He has already solved your problem and can supply a complete long stroke crank assembly for both Comets and Twins. Bonus is the price is very reasonable.

 

[oexing]

Norman,
I have never come across nitrided cranks in pressed up designs, usually nitriding is only done to plain bearing car or truck engine cranks to extend life of journals. You may be right with very poor quality low strength material but then I would never accept crappy steel in my engines.
The original Vincent cranks are not overly hard steel, allright, but application of a good EP lubricant on the crank pin and bore should be good to save press fits without seizures. But then, a standard Vincent crank web is not suitable for parallel press fits, the bore just too short for a rigid assembly, due to the counterbore for the crankpin nut. For a 40 mm pin I machine the crank bore 0.10-0.11 mm undersize so this is quite some press fit. The pin has to have a nice polished radius at its edge so as not to score the bore - plus some EP lubricant.

Vic

 

[Phil Hogg]

My experience with Nitrided flywheels is from rebuilding Jawa/Eso speedway motors. They have hardened flywheels and you can rebuild them several times before the fit goes, moreover they go together really nicely. I used to scramble pre 65 class with a two valve motor in a Mettisse some years ago. Funnily enough that got bored and stroked to 600.