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66mm piston with 30mm comp height?

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66mm piston with 30mm comp height?

Postby vegansydney » Mon Aug 09, 2021 5:23 pm

I'm looking for a 66mm piston with a 30mm compression height for a piston ported project I'm working on. Any recommendations for pistons without cutouts for reeds or boost ports?

A +2.0mm TS185ER oversize is 66mm, but ideally I'm looking for a 30mm comp height, rather than 32mm.
Last edited by vegansydney on Tue Aug 23, 2022 10:53 pm, edited 2 times in total.
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Re: 66mm piston with 30mm crown height?

Postby dscscotty » Mon Aug 09, 2021 9:22 pm

30mm comp height is a tough one, possibly look at muggello 200's I'm sure there's a 30mm (116 rod) version that may be suitable
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Re: 66mm piston with 30mm crown height?

Postby Fast n Furious » Wed Aug 11, 2021 12:42 am

Syd.......Have you considered using a 30mm CH windowed piston with a reedvalve inlet manifold?
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Re: 66mm piston with 30mm crown height?

Postby lofty » Wed Aug 11, 2021 8:58 am

webster used to weld up windows in reed pistons apparently.. I always thought this sounded a dodgy and a lot of hassle, but its a (maybe bad) option..
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Re: 66mm piston with 30mm crown height?

Postby dickie » Wed Aug 11, 2021 1:26 pm

lofty wrote:webster used to weld up windows in reed pistons apparently.. I always thought this sounded a dodgy and a lot of hassle, but its a (maybe bad) option..

Sounds like a recipe for disaster to me! :o
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Re: 66mm piston with 30mm crown height?

Postby corrado » Wed Aug 11, 2021 3:20 pm

I'd try AF, maybe something in the Wossner range as the 70mm comes without windows and they cut the window in for the RB kit.
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Re: 66mm piston with 30mm crown height?

Postby Warkton Tornado No.1 » Wed Aug 11, 2021 6:44 pm

The DT 175 piston had it's relevance prior to further knowledge becoming available. They seemed the only option available for Group Four engines & a good choice for HPC. Nowadays, with two stroke tuning, the lowering of primary compression has a more useful effect.

My preference with a long rod engine would be something like a 1 mm oversize Polaris piston & use a packer, but that's not the answer in this case.

I prefer to select pistons likely to be stronger than those intended for Lambrettas but am unaware of any that will suit this particular request.

However, there may be a NOS '175 to 200 conversion piston' available somewhere. I have an Ancillotti Dinamin NIB item as a museum piece (I guess!) but that is oversize(!) & is missing it's Dykes top ring.
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Re: 66mm piston with 30mm crown height?

Postby martyn dwane » Thu Aug 12, 2021 11:29 am

dickie wrote:
lofty wrote:webster used to weld up windows in reed pistons apparently.. I always thought this sounded a dodgy and a lot of hassle, but its a (maybe bad) option..

Sounds like a recipe for disaster to me! :o

I had two piston`s done like this in the 80`s (cant remember why !) neither failed in use, both done by Taffspeed.
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Re: 66mm piston with 30mm crown height?

Postby Scooterlam » Thu Aug 12, 2021 3:09 pm

Look up grampian
They have loads of piston data on line.
Quite frustrating trying to compare though
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Re: 66mm piston with 30mm crown height?

Postby vegansydney » Sun Aug 15, 2021 11:44 pm

Thanks for all suggestions! Much appreciated.

The 66 x 30mm Mugello looks ideal, except is has a boost port cut into it already (picture below). The Scuderia Lambretta Veloce kit has an option for a 30mm CH piston but as they're not widely available yet, I'm uncertain if it also has a boost port cut into it.

Running a reed manifold seems like added work and expense, particular as this will have very tame port timings.

I've also emailed AFR and they said to call. Wish me luck! :lol:

Image
Last edited by vegansydney on Tue Aug 23, 2022 11:32 pm, edited 1 time in total.
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Re: 66mm piston with 30mm crown height?

Postby Warkton Tornado No.1 » Sat Aug 21, 2021 12:31 pm

vegansydney wrote:Thanks for all suggestions! Much appreciated.

The 66 x 30mm Mugello looks ideal, except is has a boost port cut into it already (picture below). The Scuderia Lambretta Veloce kit has an option for a 30mm CH piston but as they're not widely available yet, I'm uncertain if it also has a boost port cut into it.

Running a reed manifold seems like added work and expense, particular as this will have very tame port timings.

I've also emailed AFR and they said to call. Wish me luck! :lol:

Image


The window in the Mugello piston will not stop it from functioning in a bore that has no port, so that could be used.

I'm not sure why you wouldn't simply use a base packer with a piston of 39 mm compression height.......unless you think HPC is something worth having? Ha! Very obviously, I don't :roll:

As for reed valve manifolds, I'm not convinced of their worth, compared to, say, a well carburetted engine with adequate, well engined air filtration. On the other hand, a reed cylinder, with the porting designed to incorporate the reeds close to the bore (MQ springs to mind) is a different matter.
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Re: 66mm piston with 30mm comp height?

Postby vegansydney » Tue Aug 23, 2022 11:29 pm

Still looking for a decent non-reed 66mm piston with a 30mm compression height. Any recommendations welcome.

So far I've found:

  • Mugello 198cc has a 66mm x 30mm piston but it has small horizontal boost port
  • The Scuderia Veloce has a 66mm x 30mm GOL piston option, but has a large boost port
  • NOS '60s Asso 200cc TV175 pistons are hard to find, have very thick rings, and when found are usually in + oversizes
  • AF Rayspeed don't make 66mm x 30mm non-reed piston
  • all other 66mm x 30mm pistons I've found have windows pre-cut for reed valves: Imola, Monza etc..

As mentioned previously +2.0mm TS185ER oversize is 66mm, but ideally I'm looking for a 30mm comp height, rather than 32mm. Anything I've overlooked?

Thanks in advance!
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Re: 66mm piston with 30mm comp height?

Postby Warkton Tornado No.1 » Wed Aug 24, 2022 11:07 am

I doubt anything exists with such a low compression height.

For 'completeness' the TS185 compression height is shown here as 32.5 mm:

https://www.mitaka.co.uk/ROAD_BIKE_PIST ... TS185P.htm

However, on the same sight, 33 mm:

https://www.mitaka.co.uk/CATALOGUE/PISTON_DIMS_ALL.htm

That said, I've used the oversize Wiseco TS 185 piston.

Unfortunately the Scooter Restorations own brand cast pistons seem to be unavailable.

The only other piston - that I have also used - is the Polaris Indy but the compression height is even more. They are available forged with one ring or cast with two rings. Good strong pistons though & can be 'found' cheaply.
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Re: 66mm piston with 30mm comp height?

Postby vegansydney » Wed Aug 24, 2022 8:30 pm

Thanks, I'm a huge fan of the TS185ER pistons and have used them in a range of cylinders, most recently an RT195.

Unfortunately the cut ways on the 'ER' piston will be too close to the boost port on one of the cylinders I have. The non-'ER' piston requires a ring peg relocation--which I've had done (by a professional) in the past, but trying to avoid if possible.

The Mugello 198 piston should work for the other cylinder I have (no boost port) and in the meantime, I'll continue to explore alternatives.
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