Author Topic: V75 to V75-4V conversion piston weight  (Read 4508 times)

Offline fingerprince

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V75 to V75-4V conversion piston weight
« on: March 27, 2017, 08:19:23 AM »
Hi to all readers,

I am doing the conversion from my '95 V75PA into a V75-4V. I am using Lario heads.
I have all the parts I need to do the conversion.




I have found the original V75-4V pistons, but they are 40 grams heavier than the standard V75-2V pistons.




This weight difference might cause vibration issues.
When I look at the part numbers for the crankshaft from the V75-4V and the later crankshaft, I see that they are different (for the V75-4V it is 27064285, for the later 2V models it is 27064185).

Here are my questions:
- Does anyone know what the difference is between the 2 crankshafts (does it have to do with the weight difference of the pistons)?
- Would this weight difference make a big deal, if I use my old crankshaft, without balancing the new combination?

Regards

Offline SJM

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Re: V75 to V75-4V conversion piston weight
« Reply #1 on: December 03, 2018, 03:07:02 AM »
If you use the Lario pistons in a 750, the compression ratio will be much too high, as you will have the same clearance volume in a larger capacity cylinder.
« Last Edit: January 04, 2019, 03:17:02 AM by SJM »

Offline Chuck in Indiana

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Re: V75 to V75-4V conversion piston weight
« Reply #2 on: December 03, 2018, 02:34:00 PM »
I would think something will have to be done. 40 grams is a lot. (thinly disguised bump to the top)
Welcome to both of you to WG..  :smiley:
Martin in Australia is working on the 4V problem as we speak. Maybe he'll show up..
Chuck in (Elwood) Indiana/sometimes SoCal
 
87 AeroLario
95 Skorpion tour
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Offline jacksonracingcomau

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Re: V75 to V75-4V conversion piston weight
« Reply #3 on: December 03, 2018, 04:54:17 PM »
I would think something will have to be done. 40 grams is a lot. (thinly disguised bump to the top)
Welcome to both of you to WG..  :smiley:
Martin in Australia is working on the 4V problem as we speak. Maybe he'll show up..

mine is 650, did not change balance, std pistons.rods crank
best ref here is MWren build of few years ago. think Mike /Todd ended up making new pistons or maybe shaving weight off 4v
But simple answer is yes balance crank
I found lots, most importantly, check everything, esp actual seat pressures, installed heights, coil bind etc, is not as simple as throwing valve springs in.
problems with mine far more from previous fixers than factory
interesting compression lario v targa, but do not know actual differences, parts book a good start.
but check clearances everwhere, assume nothing
Hope Mike chimes in, that bike might have miles on it by now
I have 600 on mine, all wot but  not enough to make me the prover yet
check out my elephant walk thread for tricky adjusters, worth the dosh imho


Wildguzzi.com

Re: V75 to V75-4V conversion piston weight
« Reply #3 on: December 03, 2018, 04:54:17 PM »

Offline Simmoto

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Re: V75 to V75-4V conversion piston weight
« Reply #4 on: December 10, 2018, 01:16:55 PM »
There was a recent thread on the Loop Frame Yahoo group, guy fitted a set of Gilardoni pistons and barrels but found the set-up vibey. Weighed OEM and Gilardoni pistons and found Gilardonis to be heavier and the bike to be vibey. He took a dremel to the pistons, removing some weight underneath until they matched OEM weights.  He was only removing 6-7 grams per side though, you might not have enough metal to lose 20 from each....and it might not be a good idea for other reasons...but worth throwing out there....
« Last Edit: December 10, 2018, 02:43:51 PM by Simmoto »

Offline fingerprince

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Re: V75 to V75-4V conversion piston weight
« Reply #5 on: January 23, 2019, 04:03:46 PM »
Update !
I found an original V75 4V crankshaft in Germany. It was in very good condition.
I did the upgrade with suzuki GN250 valve springs, and cups, Honda Acura valve stem locks.
The bike performs well,  I did 400 miles with it, and waiting for the next spring to continue riding.
With the left spares, I'm building a 750cc 2 valve engine, with modified camshaft, lighter flywheel, and higher compression ratio.
'm curious for the result!

Cheers

 

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