Long stroke crank trenches.

[LateAgain]

Looking to possibly get a 62 stroke crank requiring a trench cutting into the crankcase for the back end of the conrod clearance. Anyone had this done recently, by who and how much? A local ex-Scooterist and engineer is happy to do it but hasn't done it before, he would also like to know the going rate for such machining. I had a trench cut by a mate a few years ago but he's not local anymore and pretty chocka-block. The trench he cut was for a 60mm and from memory was about 3mm deep... anyone recommend the depth for a 62mm, or is this purely dependant on the con-rod used?

Cheers, Paul.

[Warkton Tornado No.1]

Mostly, my own trenches have been cut by me, with hand held tools. I use a sanding drum in a die grinder to rough out, then finish with various flap drums in an electric drill, then by hand sanding etc. So it’s a case of ‘suck it & see’ rather than controlled depth cuts.

I am no longer a great believer in the principle of HPC, so I don’t take the minimum on that premise. However, I do take the minimum material out only so that the strength of the crankcase is not compromised.

The trenches I would advocate are not ‘stepped’ in any way but are rounded & blended in. Less corners equates to less stress, especially sharp corners. Also, gas flow is probably better, unless you subscribe to the principle of turbulence aiding the transfer process...

Nonetheless, if I had the luxury of suitable machinery, I would use it to cut a trench based upon the stroke & connecting rod big-end diameter as you rightly suggest. Clearance of rod to case should take into account the crank flex & then some to avoid 'windage' which is a bit of a drag.

In the past, I have resorted to having the connecting rod big-end diameter reduced as well. Good rods can take it as the material is so strong, with the exception of the early AFR’s own rods which were brittle, IMHO.

[LateAgain]

Cheers for the informed reply WTNo.1...

Reading the 225 thread I found this...

Is that the PM Tuning 62mm crank (HPC) with 116mm rod?

No, I went as cheap as possible
it is the 62mm MEC RB spec from AF,they have also machined the conrod but I found out that I also need to machine some tiny parts from the crankcase.

http://www.afrayspeed.co.uk/index.php?p ... tributeID=

I've never read any bad review about this crank, yet
The guys at Scooterotica garage were also using them (machined) without problems in RB25 and other engines producing around 20-25 Hp.
I don't think that my engine will produce power higher than 20 Hp,you know that I like Clubmans and Amals MK1
If I had the money,I would have gone for a second Supercorsa 62mm from JB Tuning like the one on the Rapido.

P.S. After reading Eden's amazing blog,I decided to reject the 62mm from Tino

I use this 62mm crank in my rb engine, but the 107mm rod, Ive used it for 2 seasons it done around 17000 miles now, I renewed the big end after around 13000 just before the euro as a matter of course. The case hardening had started to wear on the big end of the rod, so that was replaced. Been a very good crank at that price not over priced like a lot of others I could mention. Highly recommend it. The crankcase needs no machining just a little filing on the mouth when the crank is at bdc

Is that with ref to the PM Tuning 62/116 rod not requiring a trench ?

[Warkton Tornado No.1]

I don’t think your question is to me, but the rods that were available almost twenty or so years ago to upgrade an Indian crank were limited, or the knowledge was limited.

I still have an unused AF rod somewhere that I was afraid of using because the one of a pair that had been fitted to a crankshaft, smashed to bits before being having any chance of being used in anger.

M*z#chelli’s were worse, @ that time, IMHO, having had one self destruct upon start up on my drive.

Fitting was by a guy that would call me down to the shop floor to show me the run-out of the rebuilt crankshafts he’d do for me.