Topic: Need 1000cc piston advice - vintage Venolias vs. new DPs

[Austrian_CB]

Hey guys,

a few might have already seen my "new member introduction" thread ... If not, here's the link! Check it out if you wanna know more about the past of 72 CB 750 drag bike. http://forums.sohc4.net/index.php/topic,169464.0.html

I'm rebuilding a 1000cc engine that was built back in the day with a bunch of performance parts, but stock rods etc.
Well I already got Cycle X super rods, hd cam and primary chains, ape studs etc.

I just have a question about re-using vintage Venolia 70.5mm pistons. The pistons seem to be in good shape, rings to now (no to minimal wear). One has a mark on the dome from hitting a valve at point what I looks like. Cylinder walls are not scored.

Is it a bad idea to re-use those pistons? Should I go with the 71.25mm DP1000R's or can I just thermal coat the Venolia's and be good?

Side question ... whats the easiest way, on a configuration like this, to figure out the thickness of base and head gasket? had copper gasket installed that's approx. 0.155" thick, base gasket was already removed when I got it.

Engine will not be used for drag racing anymore. Street use only. Would like the engine to be as reliable as possible, don't want to tear it apart all the time but neither to I have unlimited funds.

Btw engine was torn apart for leaking base gasket due to stretched studs ... go figure.

Would be a great help to get everyones opinion and hear some suggestions, thanks! 

[MRieck]

 I would put those Venolia's on the shelf, look at them and talk about the "old days".    One piece oil rings, heavy, clunky parts.
 I have 71.25 flat tops in stock that I can give you a great price on. I believe I also have 72mm flat top and high(er) compression pistons too. I can also help you with chamber cc when using the 71.25 pistons to get particular compression ratios.

[kmb69]

I would put those Venolia's on the shelf, look at them and talk about the "old days".    One piece oil rings, heavy, clunky parts.
.....

Party pooper! Don't you know how to bust somebody's bubble!     

[Austrian_CB]

Damn ... guess I have to go with new ones. And I thought I had something special  haha

I'd like to do 71.25 and keep it somewhere around 10.5:1 compression. Can I keep the existing sleeves and just have them bored out? Any good machinists who I could send the cylinder to on here?

Thanks,
Simon

[754]

 First off weigh your pistons, some were heavy some where light.., lets sed what you actually have there. .

[kmb69]

That #2 piston appears to have hit a bent or stuck intake valve at some point.

[Austrian_CB]

I know, I stated that in the original post. That was one of the reason for me asking if they'd still be re-usable. Not sure if that did any colleteral damage or not!? I was definitely a battle scar from many years ago and they just put those pistons back in ... head locks good. 

Will weigh the pistons tmrw.

[Jerry Rxman Griffin aka MuthaF'er]

Damn ... guess I have to go with new ones. And I thought I had something special  haha

I'd like to do 71.25 and keep it somewhere around 10.5:1 compression. Can I keep the existing sleeves and just have them bored out? Any good machinists who I could send the cylinder to on here?

Thanks,
Simon

MRieck has already offered his help. Won't get any better. Other members that can help are Kenny at CycleX or Big Jay at APE.

[turboguzzi]

+1 on Mrieck, would skip ONLY because of those ancient oil control rings. they remind me too much of those on my old british bikes. ok-ish for a slow turning 500 single, not for a sohc...

[Bill/BentON Racing]

Old piston's.....welll, I'd use new if possible...pins also!

[kmb69]

I know, I stated that in the original post. That was one of the reason for me asking if they'd still be re-usable. Not sure if that did any colleteral damage or not!? I was definitely a battle scar from many years ago and they just put those pistons back in ... head locks good. 
.....

Sorry, didn't read first post close enough. Just blowing through, looking at the pictures.

+1 on MRieck support. As Spanky says, "Won't get any better".

[Medyo Bastos]

I know, I stated that in the original post. That was one of the reason for me asking if they'd still be re-usable. Not sure if that did any colleteral damage or not!? I was definitely a battle scar from many years ago and they just put those pistons back in ... head locks good. 
.....

Sorry, didn't read first post close enough. Just blowing through, looking at the pictures.

+1 on MRieck support. As Spanky says, "Won't get any better".

i like to l ook at pictures too 

the only real way to tell if that piston is any good is to have it magnafluxed.  if it passes the test you can have the lands redone for modern rings.  may not be worth the effort...

[Austrian_CB]

Thanks for all the replies guys!

It's pretty obvious what everyone's opinion is! And it makes sense, I was probably trying to tell myself using the old ones will be just fine.

To the oil ring ... how is the oil ring on the new ones, 3 piece i'd guess?

To the weight of the Venolias ... #1 226.3g #2 227.3g #3 227.3g #227.3g ... all include rings.
What is the weight on new 71.25mm ones?

[PeWe]

Hi,
My JE 71.25mm pistons (DP1000) weighs 190 grams each without rings and wristpin. But my pistons are special order  since the head has opened chambers 24.4cc (std size calculation 22.5). Pistons adapted to 24.4cc and CR10.5:1

Pistons in the middle between DP1000 12.5:1 (195g) and 10.5:1 version (185g). The crown look like a 12.5:1 that is grinded off a bit.

I run them with Mike Rieck's billet block, CB750K6 street bike.

You already have a lightened crank?
Undercutted gears in the transmission to avoid unwanted jumping gears and over rev.   2 and 4 typical jumpers.

I have an APE Ultra crank w Carillos in mine, engine has never run as smooth as it does now with the lightened and balanced crank.
Plus an old lightened alternator.

I also highly recommend Mike Rieck as your HP provider/restorer, work as well as all connected parts needed in one package.

[gschuld]

Oil rings since the mid 70s have been 3 piece:  And FWIW, a s set of rings per piston is 23 ounces on big bore 70s pistons with 3 piece rings if I recall correctly. 

George

[MRieck]

Oil rings since the mid 70s have been 3 piece:  And FWIW, a s set of rings per piston is 23 ounces on big bore 70s pistons with 3 piece rings if I recall correctly. 

George

23 ounces George? Must be the Mallory filled tungsten piston rings.

[gschuld]

Whoops, that isn’t right.  I meant 23 grams.

George

[MRieck]

Whoops, that isn’t right.  I meant 23 grams.

George

Just busting B's George.

[gschuld]

I know Mike, got a Turkey day stuffing on the brain  

George

[Big Jay]

If you decide to use those pistons, I believe the rings would be Honda 1000cc Goldwing first over. And that should be a 3 piece oil ring.

[gschuld]

I was distinctly under the impression that RC included Honda factory 1mm oversized cb450 rings with their 71mm Venolia pistons and they had the one piece oil rings.  Naturally the Venolia 70mm pistons then used Honda cb450 stock bore rings.  FWIW, Venolia had an exclusive contract with RC from 1971/2 through the mid 70s when they then switched to Arias.  All the early RC pistons(Venolia)I am aware of used Honda factory rings supplied from basically across the street from RC’s Terrance California shop. 

I believe the cb500t(also 70mm bore stock) switched to the 3 piece oil rings.

The 1975 gl1000 was 72mm factory bore I think.

George

[Austrian_CB]

I can't even express on how much I learned in this thread  all that info is worth a lot.

I ended up picking up a set of 71.25mm DP1000R's from Dynoman. I was lucky that I realized they have a black Friday sale and have the piston kit for $150 off. So that's what made the decision way easier.
Will hopefully get the cylinder machine work, maybe some head work done by MRieck.

Very excited to build this motor right now ... lots of motivation on here!!

[gschuld]

That’s great Simon.  Glad you are moving along with the project.  Those JE pistons have a great reputation.  You won’t be dissapointed. 

Ask when you have questions.  You’ll get answers, hopefully the correct ones. .  Some like me pretend to know what we are talking about.  Others here have the real hands on experience.  I’m bettter with obsolete parts and useless bits of cb750 high performance history.

Please keep us updated on your progress.

George

[PeWe]

I can't even express on how much I learned in this thread  all that info is worth a lot.

I ended up picking up a set of 71.25mm DP1000R's from Dynoman. I was lucky that I realized they have a black Friday sale and have the piston kit for $150 off. So that's what made the decision way easier.
Will hopefully get the cylinder machine work, maybe some head work done by MRieck.

Very excited to build this motor right now ... lots of motivation on here!!

You need patience when you assemble the cylinder over the pistons. The oil rails are thin and rather flimsy.
I pinched one and had to order new rings that cost a lot due to the shipping to Sweden. Not available around here in Europe.

You might notice that the oil rails will get stuck into the expander when squeesing them together. I filed the inner corners just a little of the rails, a rounded shape to avoid making them to hook into the expander they must sit ON, not beside.

I found an easier way to get the cylinder to fall over the pistons with rings by the cylinders on weight without pressing it down and risk to pinch a ring. Put a screw driver into the wrist pin and moved it quickly forward-backward to vibrate down the cylinder while I carefully pressed the rings together. The 2 top rings no problem, the oil rails needs extra attention. The vibrating method worked fine!
I made my mistake since I did not have the cam chain tensioner in place. It fell outside and I had to lift cylinder to get it in again. I had 2-3 pistons in and I put the cyl back on too quick....

[MRieck]

 Yes....the oil rails are delicate