Proposed engine build musings

[tony172]

Thinking about the specs for my next engine build, commencing late summer this year.
Would like to know people's thoughts-

64mm bore, thin ring tv175 piston,
30mm crown height,
60/116 gp taper crank,
175/124/155 timing (roughly),
30mm dellorto,
Dj pipe,
Re-profiled head,
1.3 squish
Light flywheel
Af Close ratio gearbox
68% exhaust port width
17deg btdc static

Dont know sprocket sizes for use with the af box yet.

Going in a bone down superlight skelly, 11stone rider, looking for reasonable A road capability and 70-75 top, good around town

Thoughts anyone?

Thanks
Tony

[vegansydney]

Without derailing your thread, I'd be interested in what 64mm, thin ring, 30mm compression height piston you plan on using?

AFAIK there very few options for quality pistons that fit those specs, and why the TS185ER piston has been widely used for so long. Mugello 186cc with the 30mm compression height? There is also a new Wossner 64mm piston from AF Rayspeed, but uncertain of compression height. If you know of others I'm all ears

[tony172]

Whoops, my mistake, that's supposed to say 62mm. Scooter Restorations have a 62mm tv175 piston made by Diamond with 1.5mm chrome rings.
That's the piston I was planning on using
Sorry for any confusion

[tony172]

Does anyone know specs on the ring peg position of the ts185 piston?

[hendy]

I'm running a similar setup.

Gp150 bored to 62mm.
178 ex
124 tr
143 in

Goes very nicely, but I have 25mm dellorto through a drilled airbox and and old mick abbey expansion i got for £20.

So, carb and pipe wise, it's very different, but the tune is similar. I stayed lower on the inlet just from reading MB tech pages which advise against high inlet timing.

I thought the highish exhaust duration might make it a little unpleasant around town, but not at all, it's very civilised.

[hendy]

By the way, I know someone who has a DJ pipe for sale.

[tony172]

Oh that's interesting to know, lower inlet is also something I've considered after reading the MB site, and I'm glad you're finding the higher exhaust timing to be manageable, as I've always aimed for 125/180 on my vespas, with good results. Maybe I could go a tad higher with the exhaust and lower with the inlet.
Can I ask what piston you're using?
Second guessing the diamond piston now, and considering the ts185er although I'm trying to keep it from being over square.
Suzuki Pe175 62mm seems perfect but more than I really want to spend on this one
I'm aiming for the best compromise between bore/stroke and con rod length without too much faff or expense.
Thanks guys

[tony172]

Also, thanks for the heads up on the pipe but I'm really only in the planning stage, I don't want to get carried away buying stuff at this stage!

[hendy]

I used an asso 62mm, 39mm crown height.

I'm not sure it makes sense to compare vespa and lambretta port timings too much as vespa use that crank timing thingummybob technique. I'm not very knowledgeable on vespa, but that's my understanding.

I'm not sure there's a problem with being over square really. To me, you can increase bore or stroke independently with good results, but a perfectly square motor gets the maximum cc from minimum bore and stroke, so it's an inherently efficient design. Or is there something else to it?

[mick1]

75 top might be overly optimistic, i'd be surprised if you got into the 70's......settle for low 60's and you won't be disappointed.