Venolia pistons, keep or not?

[Roto36]

My 77'D has a fresh rebuild from previous owner. When I got it all I had left was tuning carbs, paint and few miscellaneous things to finish. While getting help from members here about my carb issues it soon lead me to check my compression. It was off the chart at 240 psi both sides. I had no reason to check what was in the jug until now. I found Venolia pistons inside with over sized sleeves, after some measuring I'm at 800cc and have a little over 12:12 compression. With help from grizd1 I learned how to lower my compression so I can run regular pump gas.

I checked around with my local machine shops to have material removed from the tops of the pistons to increase volume and lower CR, some shops say they're not setup for this work and another strongly recommend I leave these pistons alone because they're not something you come across everyday. One shop actually said "shaving these pistons is like taking a distinguished lady and knocking her teeth out so she can perform better" (made me chuckle...!). I'm sure it's no problem to find a machine shop to work on these but after learning more about these piston I'm having second thoughts.

This shop recommended I find a jug with matching pistons instead of shaving these. This way I can always increase things as they wear out.

So now I'm at a road block of options to consider.
- Thicker gaskets and take what I get and use octane booster?
- Find a shop, shave the damn things and move on?
- Find a matching stock jug with pistons? (What years interchange?)
- Keep or sell the jug with Venolia's?

Not wanting or needing a hod rod bike, just a cruiser for occasional overnight road trips.

Any ideas/advice would be much appreciated!

 

[scabber]

Sell the cylinders and Venola pistons. Take some pictures and put in the classified section on site. Get a good stock set of pistons and matching cylinder. You are better off staying with the lower compression stock pistons.

 

[hotdog]

Shave them to suit your needs. I'll be doing the same to my brand new Ross pistons soon enough to enable pump petrol to be used.
Measure twice, cut once - make sure there is enough meat in the piston crown to allow removal of the required alloy to set your C.R. prior to firing up the mill.

 

[TwoManyXS1Bs]

Round-off all the sharp corners on piston domes can help.
Also, recess/pocket the valves. Valve face/tops can be reduced a little, slight concave in exhaust, round-off that annular corner on intake face/top. Lotsa work for maybe 1/2 point compression drop, but at 12:1, a little makes a big difference. 240psi compression sounds like 16:1, time for some math and measurements. Do you know how to CC a head?

 

[Roto36]

Yep cc'd the head and cylinder with guidance from grizld1. Wouldn't doubt my numbers may be off a bit so I made sure to go through everything a few times. After my third cc measurement came near the first two I was pretty confidant with the results.

 

[grizld1]

Roto, the setup you have now is only usable with race fuel. When I tell you that Venolia crowns are thick enough to be shaved by .030" to .035" without risk of damage, I'm talking from experience, and not only my own; it's a common modification and any machine shop with a milling machine can take care of you. As far as recontouring the domes goes, that's fine if you have some experience under your belt, otherwise leave it to a professional speed shop; there's a lot of room for error there. If the CR is still too high when you cc the motor again, double up the base gaskets and degree in the cam.

 

[Jack]

With a 83mm bore and 63cc C/C volume you'll need at least 16 to 20CC- dome( what you're looking to achive is a C/C VOLUME OF 45CCs) or.250+ dome to match the squish area in the C/C. can you post any picures of the underside of the dome?

 

[Roto36]

 

[Jack]

Those are ForgedTrue that appear to be in excellent shape , the "RAREST" piston you ever come across and if I were you,I would sell'em for a hefty premium price or hang on to them for they are part of the XS's racing history. It's not every day you come across a gem like those What's the MM size?

 

[Punkskalar]

I'm with Jack on this! Sell me the piston/jugs/rings and I'll put them in my land speed bike Seriously, pretty please Just don't cut those!

I'd gladly help you get another Street Friendly big bore, anything Hugh's HandBuilt Related, etc...

Hugh

 

[Jack]

I'm with Jack on this! Sell me the piston/jugs/rings and I'll put them in my land speed bike Seriously, pretty please Just don't cut those!

I'd gladly help you get another Street Friendly big bore, anything Hugh's HandBuilt Related, etc...

Hugh

And who's porting that head

 

[Black Rose]

I'm with Jack on this! Sell me the piston/jugs/rings and I'll put them in my land speed bike

Hugh

Ahh now you've jumped in, Great ! Once you go you'll always come back. I'll keep an eye out for you.

Roto,

If your only looking to cruise your daily rider, there are a few folks that could put those slugs to good use. They will more than happy to set you up with a great street combination.

 

[TwoManyXS1Bs]

Ahh, the wisdom of Solomon still works...

 

[scabber]

If you had read the post he said he didn't want a hot rod bike. Just a cruiser for over night road trips. Even if he shaved the domes. It would be a hot rod bike. The 650 stock motor would fit his needs perfectly. My advice to sell. So I have first dib's on those pistons.

 

[hotdog]

I agree, onsell them.

 

[Roto36]

What's the MM size?

I'm no machinist but my trusty calipers tell me:

piston - 79.90mm
bore - 79.94mm

 

[Jack]

I'm no machinist but my trusty calipers tell me:

piston - 79.90mm
bore - 79.94mm

Those are 750CC pistons and are most likely from the early to late seventies, you can't even google the company I wish I was in the position to make you an offer( a ported head with all my little tricks is all that I could offer at this time) but my good friend Hugh would set you up with a good street friendlier combination,so what ever you do "Please Don't Cut Those Pistons" later

 

[racerdave]

Those are 750CC pistons and are most likely from the early to late seventies, you can't even google the company I wish I was in the position to make you an offer( a ported head with all my little tricks is all that I could offer at this time) but my good friend Hugh would set you up with a good street friendlier combination,so what ever you do "Please Don't Cut Those Pistons" later

Jack, your google must be broke.

 

[grizld1]

Exactly right, guys--Venolias are common and current but Forged True pistons are rare, and there won't be any more of them! Cutting down the crowns would be vandalism.

 

[Roto36]

All be damn'd, I've heard of rare finds but who would'a thunk pistons. Leaving these untouched for sure. I'll be looking to sell after I do some research and learn a bit more about them.