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rocketonarail

rocketonarail

Hero member
Location
Gloucestershire,England
Back in the early `noughties various suppliers here in the UK sold " state of the art " forged replacement pistons for Laverda triples and twins ....... Miura and Phil Todd sold them .... I got mine from Richard Slater , 80.5 mm , for the 1200 Mirage .

I believe they were made by Aso , in Switzerland , but not Laverda specific as far as I know ............. They were certainly pretty looking things , with a purple ( teflon ? ) coating for the skirts , and a crown finished to a compact disc standard , which you could see your reflection in .......

Not flat top , like the factory fitted 8 : 1`s , but with a slightly raised crown , which would give a CR in the region of 9 : 1 , I would imagine ......

The thing is , the raised crown contained cut outs , for valve clearance ........ one cut out being larger than the other , and I`m certain there was a specific way round these pistons were supposed to be fitted , probably an arrow indicator to point to the front ( exhaust valve side ) ....... It must have been that , although I can`t remember for sure ....


Now , I`m pretty certain about the following , although it was about twenty years ago , and I`m going by memory ......

............ When the pistons were positioned facing in the recommended direction , the smaller cut out was positioned under the larger inlet valve , whilst the larger cut out was positioned under the smaller exhaust valve ............ Logically , you would expect the larger cut out to match the larger valve , and vice versa , but this would mean the pistons would be fitted the wrong way around ( back to front ) , according to the instruction .

In the event , I fitted the pistons the recommended way around , figuring ( hoping ) there would be enough clearance between larger inlet valve and smaller crown cut out ......... The exhaust side of things , with the smaller valve and larger cut out presumably would be ok ..... Also , I was reluctant to fit the pistons the " wrong " way round , in case it would cause problems concerning the weighting , or balance of the pistons ..... probably not , but I don`t really know much about these sort of things .

There was also the thought that the 4C`s lift , and timing , would maybe create different clearance issues , compared with A11`s , or A12`s or whatever , when used in conjunction with these pistons .... but again , that is something I`m not sure about either ......

Didn`t have any problems over the next 15 - 16,000 miles , so that I guess was that , but I wondered if anyone else fitted these pistons at that time , and had any similar thoughts concerning this ........
 
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The connection point on the piston can be positioned not central, offset with something to do with the rotation, that cutout setup sounds really odd though.
 
Vince said:
The connection point on the piston can be positioned not central, offset with something to do with the rotation, that cutout setup sounds really odd though.
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Yes .... I looked at a picture in the Green Book at the time , which shows factory domed pistons with their cutaways ...... Tim Parker says there is an indicator arrow in the crown which should point to the front , and as a double check , make sure the larger cut out is at the rear ( inlet ) side !! ....

I decided to bite the bullet , and fitted these replacements the recommended ( but seemingly wrong ) way round ........ Your mention about the gudgeon pin placement being possibly offset makes me glad I did ....... 🫤 .........
 
Offset pin placement is not common. Every piston I've ever fitted:

a) had an arrow indicating fitment, and b) had the larger valve pocket designed to go with the (larger) inlet valve

Never seen a piston with a larger inlet pocket than exhaust pocket. Whatever was happening with those slugs, Rocket, with most examples you would have known immediately if the way you'd fitted them was arse-about because the inlet valve would have hit the crown and bent. Very weird, or very lucky?
 
piranha-bro2 said:
Offset pin placement is not common. Every piston I've ever fitted:

a) had an arrow indicating fitment, and b) had the larger valve pocket designed to go with the (larger) inlet valve

Never seen a piston with a larger inlet pocket than exhaust pocket. Whatever was happening with those slugs, Rocket, with most examples you would have known immediately if the way you'd fitted them was arse-about because the inlet valve would have hit the crown and bent. Very weird, or very lucky?
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Yes ....... I would think if well known Laverda specialists supplied these pistons , then they would have checked that the recommended fitment would be ok ...... It just didn`t seem " right " when I fitted them ...... but I just took the chance , and it worked out ok ......

In retrospect , I could have just phoned up Richard to check with him , but for some reason just went ahead and fitted them ......... must have lived dangerously back then ........ :) ........
 
As Pirahna said, never seen larger valve cut out on exhaust side-but I have seen pistons fitted backwards with no ill effects, last time was on a Caterham Super Seven. As for offset pin, manufacturers tend to off set the bore rather than the piston pin ( desaxe) so I reckon you were lucky.
 
You can Plasterceen the clearance, add plasterseen to the piston and turn the engine over and measure the clearance.
 
I did manage to bend a couple of valves once , but that was much earlier , with standard 1200 pistons and original CDI ignition still in place .........

When Richard Slater rebuilt the engine back in 1991 , at 113,000 miles , he found the valves , although looking ok to the eye , when fitted and spun in an electric drill , were actually bent ........

.... Must have been that time I missed a gear accelerating down the slip road to join the M4 at Tormarton ...... The trouble with Laverdas is that they run out of revs so early on ........ :whistle: ............
 
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rocketonarail said:
I did manage to bend a couple of valves once , but that was much earlier , with standard 1200 pistons and original CDI ignition still in place .........

When Richard Slater rebuilt the engine back in 1991 , at 113,000 miles , he found the valves , although looking ok to the eye , when fitted and spun in an electric drill , were actually bent ........

.... Must have been that time I missed a gear accelerating down the slip road to join the M4 at Tormarton ...... The trouble with Laverdas is that they run out of revs so early on ........ :whistle: ............
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When my french market Jota was rebuilt by Grant Duguid, he also found at least one bent valve.
I think that I know when that happened, a missed gear when wringing its neck.
Paul
 
The larger cutout should match the larger of the valves, that part is straightforward. The Italian Asso pistons, OE supplier of forged pistons to Laverda, had an arrow on the INSIDE of the piston which had nothing to do with fitting direction. This was misleading for many.
Off-axis gudgeon pins are quite common, these help to decrease stresses in the conrod and aid smooth running.
piet
 
sfcpiet said:
The larger cutout should match the larger of the valves, that part is straightforward. The Italian Asso pistons, OE supplier of forged pistons to Laverda, had an arrow on the INSIDE of the piston which had nothing to do with fitting direction. This was misleading for many.
Off-axis gudgeon pins are quite common, these help to decrease stresses in the conrod and aid smooth running.
piet
Click to expand...

That`s interesting ........ It was some time go I fitted these replacement pistons , I can`t remember exactly , but I`m sure there was some sort of indication on them.... Whether it was in the form of an arrow on the inside , as per original fitment pistons , or some kind of marking elsewhere , I`m not sure ........

If the marking was on the inside , then it looks as though I did indeed fit them the wrong way round ....... :oops: .......

By the sound of it , the arrow , wherever it was situated , should have been ignored , and the larger cut-out matched to the inlet valve ...... which obviously makes sense ...... ( but when you see an arrow pointing the other way ....... ) ......

......... But the main reason I fitted them the way I did , and followed the arrow marking , was that I had the impression , ( rightly or wrongly ) , that these were not Laverda specific pistons , but much more likely off the shelf items , which just happened to be suitable for Laverda fitment , with cutaways that gave adequate clearance no matter which way round they were fitted ...........

Maybe the current keeper of 1200 * 1637 * , ( wherever it is now ) , should take a peek inside and find out for certain where the cutaways are , and which way the arrows are pointing , and maybe swap them around if needs be .......... ( On second thoughts don`t do that .... pistons which have already bedded in may not take kindly to being reversed in their bores ... ) ....

If everything seems ok best just leave things alone .... It`s been twenty years and at least 15,000 miles since they were fitted , after all .......

Having said that , If I still had the bike, I would be starting to take a look inside now , just out of curiosity ....... :) ...........
 
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Doesn’t matter if they were laverda-specific or not, the larger cutout accommodates the larger valve .

piet
 
rocketonarail said:
That`s interesting ........ It was some time go I fitted these replacement pistons , I can`t remember exactly , but I`m sure there was some sort of indication on them.... Whether it was in the form of an arrow on the inside , as per original fitment pistons , or some kind of marking elsewhere , I`m not sure ........

If the marking was on the inside , then it looks as though I did indeed fit them the wrong way round ....... :oops: .......

By the sound of it , the arrow , wherever it was situated , should have been ignored , and the larger cut-out matched to the inlet valve ...... which obviously makes sense ...... ( but when you see an arrow pointing the other way ....... ) ......

......... But the main reason I fitted them the way I did , and followed the arrow marking , was that I had the impression , ( rightly or wrongly ) , that these were not Laverda specific pistons , but much more likely off the shelf items , which just happened to be suitable for Laverda fitment , with cutaways that gave adequate clearance no matter which way round they were fitted ...........

Maybe the current keeper of 1200 * 1637 * , ( wherever it is now ) , should take a peek inside and find out for certain where the cutaways are , and which way the arrows are pointing , and maybe swap them around if needs be .......... ( On second thoughts don`t do that .... pistons which have already bedded in may not take kindly to being reversed in their bores ... ) ....

If everything seems ok best just leave things alone .... It`s been twenty years and at least 15,000 miles since they were fitted , after all .......

Having said that , If I still had the bike, I would be starting to take a look inside now , just out of curiosity ....... :) ...........
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It's now residing in Barry, South Wales and leading a very sedentary life....😉
 
sfcpiet said:
The larger cutout should match the larger of the valves, that part is straightforward. The Italian Asso pistons, OE supplier of forged pistons to Laverda, had an arrow on the INSIDE of the piston which had nothing to do with fitting direction. This was misleading for many.
Off-axis gudgeon pins are quite common, these help to decrease stresses in the conrod and aid smooth running.
piet
Click to expand...
And they reduce engine noise
 
As well as maybe / possibly / definitely wrong way round pistons ; a poorly fitting exhaust made up of components from three different sources ; a tendency ( no , make that a certainty ) to jump out of first gear when subjected to even the slightest load ; oil leaks from the exhaust ports that would make even the Amoco Cadiz not worthy ; a huge false neutral between second and third when " going for it " ( more bent valves , anyone ? ) ; a clutch that was as soggy as morning after cornflakes ( and about as much use in heavy traffic ) ; basic Hagon rear shocks that initiated a gentle weave on any uphill corner I dared to take at more than 50 mph ..........

........ Despite all this it was a really fun , reliable , and from several paces away , still a good looking bike after 41 years and 226,000 miles ( when I last saw it ) .......... Still more than capable of doing all the usual Laverda stuff from 5500 rpm onwards ......... It got used .........

..... Thanks for the info regarding it`s current whereabouts Alan C (y) ......... If the current keeper is getting tired of moving it out of the way to get to his lawnmower all the time , I could almost be tempted to take it off his hands , sort out all the " problems " , keep it for a year or two to make sure everything`s ok , then return it to him again ......... All free of charge , obviously ........... :) .............
 
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... I`m starting to get all nostalgic now .......

1200 * 1637 * just a couple of weeks before I sold it , Nov 2019 , with 225,610 miles on the clock , ( 212,531 by me ) .........

... That`s 363,084 km since new , ( 342,035 km by me ) ..... if you`re metrically minded .......

Images from a Kodak print , so not exactly HD .......

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... and if you`re still with me ........ a couple more from about the same time .... Slaters shop window ( Sunday , so it was closed ) .....

... Orange things are a Palmelli 878 , and a 5000 / 8000 ( someone will know ) SFC ....... ( Did all 5000 batch have protruding headlight rims ? ... I`ve forgotten .... ) .......

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... and finally ..... if you`re still interested .... the well equipped workshop where all the Laverda piston swapping took place ....... present incumbent in search of a missing dipped beam ...... burnt red / yellow leading to dip relay ....... 28/0.30 should fix it ( hopefully ) ......

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