Advice on GT186 crankshaft, Rapido Italy good enough?

[The prisoner]

Hi,
i'm rebuilding my engine with a GT186 kit at the moment, will be fitted with 25 phbl and ancillotti clubman (maybe an other later ).
Concerning crankshaft, i've got an Italian Rapido "albero motore LAM CORSA 200CC nero corsa 50 biella ramata lungh." with bronze rod and black webs in the shed.
I don't know if it's good enough, compared to a GP200 racing MEC EUR for exemple?
Someone fitted an other type of crank with the Rich T kit?
HPC crank? Different dimension (60/107 or 110)? Modified rod or pin? Modified webs?
Cheers for help.

[Rich_T]

The vast majority use stock production cranks 58 & 60 stroke with 107 rod. There are a couple out there with 110 rods and a packing plate and I know one that had the SCC HPC crank in it which went very well (the advantage being low drag on the crank rather than higher primary compression).

For a standard crank Maz or MEC 58/107 cranks are very good. I personally don't know of anyone running modified webs with a GT kit, most (90%) want to keep the conversion reversable or minimal changes/stock looks.

I don't recognise the make of your crank but provided it is in good condition and is or does not twist it should be OK.

[The prisoner]

The vast majority use stock production cranks 58 & 60 stroke with 107 rod. There are a couple out there with 110 rods and a packing plate and I know one that had the SCC HPC crank in it which went very well (the advantage being low drag on the crank rather than higher primary compression).

For a standard crank Maz or MEC 58/107 cranks are very good. I personally don't know of anyone running modified webs with a GT kit, most (90%) want to keep the conversion reversable or minimal changes/stock looks.

I don't recognise the make of your crank but provided it is in good condition and is or does not twist it should be OK.

Hi Rich,

cheers for advice.
I had reserved a black web MEC 58/107 GP200 race crank for that use but gave it to a friend in emergency and recover this Rapido one instead, but it's new (still in package) so not twisted
Don't intend to reverse the conversion without changing crank because originally it's a TV175.
I'll be interested in having feed-back of people who have fitted 60 stroke or 110 rod: better torque, sweeter engine?

[Rich_T]

The kit was designed around 58 stroke 107 rod. Technically, a 110 rod should be better and a 60 stroke crank does increase torque, usually because of the capacity increase but it does change the piston velocity for the same given RPM. Some say that the 60 stroke cranks vibrate more, technically this is right but how much it is noticable compared to a change in engine mounts, for example, is highly debatable.

The case against 60mm stroke cranks is reliability. The material between the pin and the outside of the webs gets thin and stretches, reducing the tightness of the fit and sometimes leads to twisted cranks. I have a 60mm stroke crank engine I'm working on now, but the pin is welded (exactly for this reason).

Personally, I have not built a GT with a 110 rod. You'll have to ask around for that.

If the casings are TV I would definately advocate leaving them exactly as they are, the kits still go pretty well even when the transfers are not matched.

[The prisoner]

Ok.
Understood about 60 stroke crank weakness, let us know what are the results on torque once you'll have finished this engine.
Will MP you for other questions (Porcupine head...)

[Yanker]

Hi,
i'm rebuilding my engine with a GT186 kit at the moment, will be fitted with 25 phbl and ancillotti clubman (maybe an other later ).
Concerning crankshaft, i've got an Italian Rapido "albero motore LAM CORSA 200CC nero corsa 50 biella ramata lungh." with bronze rod and black webs in the shed.

Can you please double check the label? does it not read albero motore LAM CORSA 200CC nero corsa 58 biella ramata lungh.

It is most likely a typo? and the latest packaging of the familiar black webbed ex 'MEC' crank. Corsa 58 would mean 58 stroke (standard). Biella is 'con-rod' Check the rod big and small end centre length for the rod length. I understand theat the MEC brand may be in some financial/contractual trouble but the same cranks are still being supplied directly from manufacturer to UK wholesalers packaged as you described (black box).

[The prisoner]

Your right Yanker, it's written 58 and not 50...sorry.
Will post a picture of this crank and package asap.
It looks very close to a MEC but rod is bronze in color, not polished. Small end bearing included seems a beat chip but can replace it by something better (13 or 14 pins roller bearing)?

[Rich_T]

If you're fitting a GT kit you get a new wide SE bearing in any case and if this is the original manufacturer for MEC and 58 stroke then the crank is perfect for the job.

[byron]

... it's new (still in package) so not twisted

doesn't necessarily follow... I always get cranks checked for trueness etc before fitting, even new, unused ones, some of which have been out...

[The prisoner]

Byron, Yanker and Rich, here are some pics of the "new so not twisted" crank:



Bronze rod:



And black webs:





And the SE bearing, but you were right Rich , there is a large (22,5mm) new one in the Mitaka piston box included with the new GT kit.
No shims needed for that type of piston and small end 22 mm bearing i think