Need help: Strange 88mm pistons in my engine

[rolf j]

Hi,
I thrashed a piston at the race last weekend. The bike is originally a V7-Sport, but the PO has put in 88mm pistons, 78mm crank and a head that resembles LM1-2, surely using the LM1-2 size valves (44/37). Perhaps this is an old performance kit? No idea, I only know the job has been done a VERY long time ago.

The piston I found in there has the following measurements:

Diameter: 88mm

Deck height from top wristpin: 24,2mm which is near enough the 24,4mm that Guzziology states is the most common one in the Tontis (I may even have measured inaccurately). No problems so far.

The dome height is 6,5mm which according to Guzzilology is not found originally in any Guzzi engine.
The 88mm pistons come originally with the following dome heights: 1,8mm - 4,1mm - 15,0mm.

Any suggestions how and where to source a piston like this?

Would it be possible to mill off 8,5mm from the dome of a LM4 piston? (15,0mm originally). Is it enough material up there to do such a crude thing?

rolf j

 

[rolf j]

Would it be possible to mill off 8,5mm from the dome of a LM4 piston? (15,0mm originally). Is it enough material up there to do such a crude thing?

Just heard from a friend that the LM4 has an approx 9,4mm thick "roof" so the milling-off option seems to be out. What now?

 

[Skeeve]

Would it be possible to mill off 8,5mm from the dome of a LM4 piston? (15,0mm originally). Is it enough material up there to do such a crude thing?

Just heard from a friend that the LM4 has an approx 9,4mm thick "roof" so the milling-off option seems to be out. What now?

Get out a Wiseco catalog & look thru the VW pistons the same way Tonti did when he was collaborating with the racers when they first started hotting up the loop frames back in the 60s! That's probably the original source for your odd 6.5mm dome ht. that you discovered upon tear down... Good luck!

 

[guzzigray]

SP3's use 88mm pistons with 44/37 valve heads. That might be a starting point for replacement. Compression wouldn't be that high but you could mill the heads.

 

[Hudriwudri]

Hi,


Any suggestions how and where to source a piston like this?

Would it be possible to mill off 8,5mm from the dome of a LM4 piston? (15,0mm originally). Is it enough material up there to do such a crude thing?

rolf j

Hi rolf

here are some adresses for pistonmakers who produce pistons for the guzzi, judging by me i would rather go for the CPS pistons as the company is really nice and easy to deal with besides that quite some guzzi teams seem to use them in italy.

CPS Costruzione pistone speciale:

http://www.pistonispeciali.it/

In case you dont see your particular need call or fax them i assume they also galdly supply you with a pistons blank that should suit all your needs.

Wahl Spezialkolben:

http://www.wahlspezialkolben.de/

As mr. wahl is a well known specialist of one off pistons there is not much to say bout his quality besides i guess it could get a lil pricey.

at the end you could also give woessner http://www.woessner-kolben.de/ pistons a call, alsoe very nice to deal with and they might also be able to supply you with a suitable piston or a blank.

to begin with i would try to give cps a call/fax.
Otherwise both wahl and woessner should be prime candidats to find VW-piston, even though the valve cut outs might be wrong of which im not quite sure though?

with machining material off a piston top especially on a race bike i would be quite carefull.

kind regards

christian

Oooops: forgot You could also try to give mr. bruno scola a call as he is a "supernice" Guy and i assume he should also talk english, and frankly, if he doesnt know i would not know who would :lol:

 

[Chris R]

You could also try to give mr. bruno scola a call as he is a "supernice" Guy and i assume he should also talk english, and frankly, if he doesnt know i would not know who would

Bruno is a super nice guy but he doesn't speak english and most italians would say he doesn't speak italian (No disrespect)! He is from Bergamo so he has a very heavy bergamasci accent which can be hard to understand for anyone who has learned italian as a second language and non-locals.

Bruno is very much old school; polish and knife edge everything in sight, stick in a big cam, big vavles and big lumpy pistons, polishing and porting by intuition (no flowbench) so he might know where your big lumpy piston came from. The only other pistons I know of were done by Cosworth (very nice and expensive as expected and available through RACECO UK) and RAM (no idea who they really are but Pete Roper has bought stuff from them).

This is in no way a criticism of Bruno - last time I was there he treated me to a very delicious lunch and was thoroughly delightful as I struggled to understand what he was saying.

 

[rolf j]

Thanks a lot guys!

I'll follow these leads and hopefully through the winter I'll get it up&running again. Coming back to you about the results.

I've done the teardown now and except for the mess in the top end thing do not look too bad. The slack in the wrist pins are huge - sensational! One valve lifter ('cup') has broken in two :shock: and messed up its bore so a bit of machining&oversize lifters will hopefully save the engine block. Crank and big ends look like they came off the factory line.

End of season for me now, next race is in April-2011!

 

[motoguzznix]

You just need to get a piston for a LM123 88mm upgrade kit.
More than 20 years ago I bougt such a kit in Mandello to increase the capacity of my LM2 to 948,8 cc. This year I renewed a friends engine with new cylinders/pistons and the pistons were exactly the same than those 20 years ago: even the weight of piston/pin was within 1 g. Dome height was 7 mm which is close enough to yours.

 

[rolf j]

You just need to get a piston for a LM123 88mm upgrade kit.
More than 20 years ago I bougt such a kit in Mandello to increase the capacity of my LM2 to 948,8 cc. This year I renewed a friends engine with new cylinders/pistons and the pistons were exactly the same than those 20 years ago: even the weight of piston/pin was within 1 g. Dome height was 7 mm which is close enough to yours.

More than likely that is the one!
I've got the piston out now and find it is marked asso-w and a number at the bottom, which I interpret to mean Asso Werke, an Italian piston maker (would have thought it was German judging form the name!). I've contacted the factory and quoted the number, but not yet a reply.

 

[guido preciso]

The piston used in some old V7 racing conversions could be also Mahle parts offered by the famous BMW-Schintzer automotive tuner.

My own V7 sport (in S3 trim after the last tuning step in the mid seventies) was tuned and raced in the early seventies by the F2 champion Vittorio Brambilla (a champion on two wheels , too) and those forged types were fitted also in his own March Beta powered by two liters BMW four, which he succesfully racend in F2 european championship.
My own bike dispacement is 982 cc, with short stroke.

Note: Bruno Scola was born in Mandello, not far from Lecco, so he is not a Bergamo man and abslolutely doesnt' speak or understand the Bergamo dialect but "laghee" (as for "Lecco lake area inhabitant") :lol:

His way of work is traditional but not bad, and he is a nice person..also if is rather difficult to have a pizza payed by him... :lol: :lol: :lol:

Cheers

 

[rolf j]

After studying a few cylinder heads I now seem to understand what the previous owner did some time long back: The head was originally a smallvalve head which has a smaller combustion chamber than the mid-valves of LM1-2, 3mm difference in diametre and a bit on the depth as well. He has fitted mid-size (LM1-2) valves and widened the chamber to make it into a strange ovale shape, probably in order to adjust down the compression when the slightly domed (7mm) pistons went in. I now have to start all over again due to a well and truly crunched up head and I am now debating whether to make it a smallvalve or a mid-valve. A cam with higher lift and a bit more duration is going in as well. I eventually found pistons with flat deck, a pair with 7mm dome and a pair with 10mm dome so I have a few options at hand. Lots of experimenting coming up, fun!!

 

[motoguzznix]

I would go for the LM123 7mm dome pistons.
If you put them under the standard small valve combustion chamber which has 9.2 CR with G5/Cali2 pistons, CR rises to 12:1. This will be lowered by the mods already done in the combustion chamber and so chances are good to get a driveable CR.
With 9mm domes it is unlikely to get a working CR apart from the problems with piston to valve clearence.

 

[rolf j]

I would go for the LM123 7mm dome pistons.
If you put them under the standard small valve combustion chamber which has 9.2 CR with G5/Cali2 pistons, CR rises to 12:1. This will be lowered by the mods already done in the combustion chamber and so chances are good to get a driveable CR.
With 9mm domes it is unlikely to get a working CR apart from the problems with piston to valve clearence.

Definately going along with your ideas here!

The fun part is that I've lately sourced enough parts to build a second engine, but don't know how it will work for the 2011 season yet, just a bonus if it becomes a running reality. A set of sleeved 94mm cylinders&pistons, roundfin, that actually has been in use so it is more than just theory. The sleeving has been done by a Swedish Guzzi engine builder who has a good reputation. Plenty of worries, dummying-up and tests though before the start button will be pressed!