Oddball engines and prototypes

**Flettner** · 17th July 2018, 11:12

crank parts, ground shafts on Central pin are 25mm dia.
Perhaps in the future i might bring them up to 26.

**Michael Moore** · 17th July 2018, 14:15

It seems like better steel in the parts to allow higher press fits would be the best way to go. OEM 2T cranks don't seem to take much pressure, but something like a Ducati 750 bevel or Laverda 750 gets a 40T press groaning. I'm sure some of that is due to the size of the pins, but those two bikes use some pretty good steel that doesn't mush out of the way.

**jato** · 17th July 2018, 15:18

years ago i pressed apart a never-been-rebuilt honda rs125 crank just to see what honda do on their race engines. from memory (a dodgy one i'm afraid) it was something around 12 to 14 ton to push it apart and it had .09mm or so interference on a 24mm pin - quite a surprise but it wasn't anywhere near as "flexible" as a motocross crank when subjected to experiments in the press. as mentioned , to handle the fit i'm sure you need a tough steel with a hard bore ($$$) . certainly a few mm of tig welding is the economical solution. the loads from centrifugle (or centripetal if you like to call it that) force cycle 4 times per rev on the pin to webs and to a degree into the main journal so you can see why engines love to dis-assemble themselves at high revs... money keeps them contented for a while...

**Flettner** · 17th July 2018, 16:58

Ha Ha yes money keeps them contained for a while, love it.
just found in my boxes of stuff a ground pin ( with the gear machined on it, made from EN39B ), measures at 0.05 press. Bit light I think, I've made plenty more I see but not ground yet. I'll take these out to 0.08 / 0.1
Crank is nitrided 4140, so a resonable steel.

**husaberg** · 17th July 2018, 19:55

Honda used to have two charts for selective fitting big ends and bigend mains based on the crankpin and pin hole diameter the big ends were then colour coded
kind of like this yamaha had a similar system, but you had tocorrect their own slapping them together and fit them yourself after delivery of the TZ.
https://images.cmsnl.com/img/partsli...32e02_a34e.gif
I have always wondered with the RS125 as Honda never sold bits, only complete cranks maybe they believed they were not up to repeated use with tight pins.

**Grumph** · 17th July 2018, 22:20

Originally Posted by husaberg

I have always wondered with the RS125 as Honda never sold bits, only complete cranks maybe they believed they were not up to repeated use with tight pins.

I'd thought that too - but local to me they seem to be surviving rebuilding OK, so I'm now assuming it was simple greed on Honda's part....

**guyhockley** · 18th July 2018, 07:22

Originally Posted by Grumph

There were two 350 triples built here. Jim Cashman built the C3 which was raced in the support class of the Marlboro Series. He cast his own piston port water cooled barrels. One of them featured on the Westoby bucket single I put up in the chassis thread ages ago.

The other I know less about. Built at Boyles in Wellington, I remember it as air cooled. It was in a Steve Roberts built TR250 frame with the usual Ceriani forks and brakes those had. Boyles were at the time the leading Suzuki tuners in NZ - and Keith Turner's TR500 used a Boyle engine to get runner up in the 500 World title. Geoff Perry nearly won Daytona with another Boyle engine.
I remember Dale Wylie riding it at a Hawkesbury meeting ( a country roads circuit ) and winning nearly everything.

Husa - Wallace is fighting his way through a batch of T250/T20 cranks at present.

Thanks, Greg.

A different triple:

https://www.bonhams.com/auctions/24494/lot/362/

**guyhockley** · 18th July 2018, 07:32

Not suggesting it as a solution for the Flettmotor, but thought this was interesting if the claims are true.

http://www.generalpolygon.com/why.htm

**Flettner** · 18th July 2018, 08:14

you see some pressed crank pins with grooves cut into the surface, say six or so generally. I'm guessing these are so some of the distorted press fit, microscopicly, distort down into these grooves helping to assist drive? I wonder this might make subsequent pressing less effective?

**Grumph** · 18th July 2018, 16:12

Originally Posted by Flettner

you see some pressed crank pins with grooves cut into the surface, say six or so generally. I'm guessing these are so some of the distorted press fit, microscopicly, distort down into these grooves helping to assist drive? I wonder this might make subsequent pressing less effective?

I don't know about less effective - but it certainly makes alignment easier on reassembly. A while back, Barry Lynch was showing me micro grooving on a late crank. That one was deliberate - but he was also talking about rough edges on the holes in crankwheels leaving grooves in shafts which he liked as it helped establish alignment when setting up to press back together.
Sadly Barry has sold up and moved to Husa's side of the hill. Another precision engineer gone.

**husaberg** · 18th July 2018, 20:34

Originally Posted by Grumph

I don't know about less effective - but it certainly makes alignment easier on reassembly. A while back, Barry Lynch was showing me micro grooving on a late crank. That one was deliberate - but he was also talking about rough edges on the holes in crankwheels leaving grooves in shafts which he liked as it helped establish alignment when setting up to press back together.
Sadly Barry has sold up and moved to Husa's side of the hill. Another precision engineer gone.

I remember that name Was it BE RT or the one just one bock over from RT?

**guyhockley** · 25th July 2018, 05:47

Latest edition of Classic Racer magazine has a report on the Pukekohe classic festival. There's s a small, uncaptioned picture of a DIY Ducati Supermono (air-cooled). Think I've found it...

"This unusual Ducati single caught my eye. There was something very ‘right’ about it, even if its provenance was somewhat head-scratching. A chat with owner and builder Andy Gourlay revealed the bike is a ‘fusion’ of half a 900 top end, a 750 bottom end (with custom balanced crank), the front part of a ST2 frame with fabricated rear, a 916 tank and various other Ducati, bespoke and universal parts."
From: https://www.rideforever.co.nz/news-a...festival-2015/
Nice job!

I've just checked, and there's been nothing from Will since 28th May. Anyone know if he's OK?
Wil, you out there?

**Grumph** · 25th July 2018, 06:14

Andy's a friend of mine - and another friend rode his GS1000S up from ChCh to ride the Ducati at Pukekohe. I've never seen it in the flesh but I understand the internals are same-same as a Supermono insofar as the balancing and crank arrangements go.
He's a clever engineer - and yes, Guy another of the Yorkshire Gourlays.

**husaberg** · 25th July 2018, 10:45

Originally Posted by Grumph

Andy's a friend of mine - and another friend rode his GS1000S up from ChCh to ride the Ducati at Pukekohe. I've never seen it in the flesh but I understand the internals are same-same as a Supermono insofar as the balancing and crank arrangements go.
He's a clever engineer - and yes, Guy another of the Yorkshire Gourlays.

Andy was the one who is or was the marine surveyor? had a macchi (marine surveyor is boat WOF rather than someone who questions Dolphins)