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Hi guys

I’m considering using a TS 185 piston in a SIL 200 barrel.

I’m thinking Mitaka 2mm oversized

The engine already has a crank installed with 116mm rod.

What are the pitfalls?

Will it work?

Is the barrel the right length? Shorten or thicker base gasket etc

Are ring pegs in right place?

Is gudgeon pin right size?

Will piston need shortening?

Will combustion chamber need rework?

What else have I not thought about?

Anyone got any real world experience of this?


Thanks

Alex

I have a ts185 64mm rod which has no issues with peg position. With a 116mm piston, I think you'll need 2mm base packers, but that's off the top of my head.

Thanks Dickie, I’d thought 3mm packer, rod being 9mm longer and crown being 6mm shorter.

You should check ring peg positions & other details on the web. Grampian used to be the best to research with a very comprehensive site. However, a Wiseco +2.0 mm TS piston worked with a Rapido barrel with no issues. I think I still have the piston....

I can't recall offhand the crank conrod details but it was probably 60 mm stroke, so the overall length must be fine for 58 mm.

alex_hughes wrote:Thanks Dickie, I’d thought 3mm packer, rod being 9mm longer and crown being 6mm shorter.

Isn't the crown 7mm shorter at 32mm versus 39mm? It doesn't matter a huge amount as you'll presumably be doing a dry build anyway. Could save a couple of quid on packers if you don't already have them though.

I've got some barrel & piston dims plus crank info for jap pistons, let me dig it out bud

alex_hughes wrote:Are ring pegs in right place?

The top peg will need relocating on the early TS185 pistons, but not on the later TS185ER ones. Not that hard for an experienced specialist to do. I've been running a converted one for 1000s of klicks for close to 2 decades. On later builds I've just purchased the ER pistons.

alex_hughes wrote:Is gudgeon pin right size?

Yes.

alex_hughes wrote:Will combustion chamber need rework?

Yes, but several people can do this no problem. Last one I had done in the UK was by MB to an RT195 head (to fit 65.0mm TS185ER in an RT195 with a 58x116 crank).

alex_hughes wrote:What else have I not thought about?

Not many oversizes past 66.0mm. I believe Wossner and Mitaka top out at 66.0mm and Wiseco at 66.5mm. Given this, for a standard 200cc, 66.0mm barrel I'd personally consider using something with a CH of 30mm (as opposed to 32mm). You may be able to get away without modifying a head using one of the following options (please check first though!)

Mugello 198cc: 66.0mm x 30mm CH piston (small horizontal boost port)
Scuderia Veloce: 66.0mm x 30mm CH GOL piston option (large boost port)
NOS '60s Asso 200cc TV175 66.0mm x 30mm CH. A little harder to find and have very thick rings, but have a couple of + oversizes.

Good luck and please post your progress so we can learn from it. Thanks!

Had a chat with Mark Broadhurst.

He’s never done this particular conversion but he will reprofile the head. He’s recommending using (in order)

1 BGM head or

2 SIL head or

3 Innocenti head

BGM head will be £150 versus the fact I have half a dozen SIL heads on the shelf… budget rules so I’ll use SIL.

SIL all the way!!!

Great heads and proved over the years on all sorts!!

Was this top end built and is it on the road?