Piston Bore Clearance

[jonno]

I have a steel lined Ts1 with wiseco piston. Just had a rebore and a heat seize lol.What is a good bore/piston clearance? I have 0.09 at the mo with a feeler gauge down the side of the piston as its slid into the bore,skirt first from the head end.

[Blaginit]

Your not measuring accurately enough you need vernier and Mic ring clearance different to piston clearance ring mb developments I'm no expert but it's not hit and miss you've got to be spot on

[Warkton Tornado No.1]

I'm not disputing anything said, but the only way that I have ever checked bore to piston clearance is via feeler gauges between the bottom of the piston & the top area of the bore, as that is the most sophisticated kit I have to hand Needs must & all that...

Anyhow, if the units of measurement are mm, & correctly converted them to Imperial, that's 0.00354" & I would be ecstatic @ three & a half thou with a Wiseco piston in a ferrous bore.

That's a tried & trusted benchmark figure for a nominal Ø66 piston/bore in my experience, despite the differing opinions of Wiseco pistons. (Some say should be tighter, others say should be looser because they are forged, but I've used probably a dozen or so of their product over the years & treat them precisely the same as cast pistons now, but they are a lot stronger)

I'd happily run with that, subject to ensuring some cross hatching remains in the bore & the piston is 'clean'

Make sure you have the correct rings for the bore, whatever you do, though!

[dscscotty]

+1

[Ken Tucky]

+2 Wiseco Pistons - best pistons I have ever used in my sprinter (iron lined TS1)
I've always used feeler gauges as per WT No 1, I too would be pleased with 3.5 thou clearance.............

Richard

[Fast n Furious]

I have a steel lined Ts1 with wiseco piston. Just had a rebore and a heat seize lol.What is a good bore/piston clearance? I have 0.09 at the mo with a feeler gauge down the side of the piston as its slid into the bore,skirt first from the head end.

In a steel line TS1 a bore clearance of 0.04 - 0.05 mm is normal for use with a high silicon cast piston. 0.09mm would be good for a cast iron cylinder.

[CHRIS in MARGATE]

Feelers every time.

[Warkton Tornado No.1]

I have a steel lined Ts1 with wiseco piston. Just had a rebore and a heat seize lol.What is a good bore/piston clearance? I have 0.09 at the mo with a feeler gauge down the side of the piston as its slid into the bore,skirt first from the head end.

In a steel line TS1 a bore clearance of 0.04 - 0.05 mm is normal for use with a high silicon cast piston. 0.09mm would be good for a cast iron cylinder.

I'm not sure why an alloy cylinder fitted with a liner would need to be treated any differently to a Rapido which is precisely the same nominal construction. Experience dictates that "0.04 - 0.05 mm" (one & a half to two thou) would cause problems in a Rapido or 'normal' linered, air cooled cylinder.

IMHO the key factor remains the expansion rate for the bore material in the case of a liner, rather than the air cooled cylinder parent material as in the case of a plated bore.

[Fast n Furious]

0.04 - 0.05mm for 66 - 70mm pistons with Nicasil plate or steel liner aluminium cylinders and 0.09mm for cast iron cylinders.
But it all depends upon certain other factors as well. Such as the type/quality of piston used and the overall cooling efficiency of the motor.
The cooling efficiency is mostly ignored or overlooked by most engine builders as it can be quite an involved piece of engineering to improve it.
I've seen cowlings that are so bad you would be better off running without any fitted at all. Of course when it goes wrong, its the poor piston that gets the blame and not the lousy cooling system.

[Warkton Tornado No.1]

0.04 - 0.05mm for 66 - 70mm pistons with Nicasil plate or steel liner aluminium cylinders and 0.09mm for cast iron cylinders.
But it all depends upon certain other factors as well. Such as the type/quality of piston used and the overall cooling efficiency of the motor.
The cooling efficiency is mostly ignored or overlooked by most engine builders as it can be quite an involved piece of engineering to improve it.
I've seen cowlings that are so bad you would be better off running without any fitted at all. Of course when it goes wrong, its the poor piston that gets the blame and not the lousy cooling system.

We must “agree to disagree” when it comes to bore materials of any substantial thickness. I simply fail to see how the greater coefficient of expansion in the aluminium finned jacket can ‘take’ the substantial cast iron/steel liner with it (as it heats up) to grow in the same proportion! In fact, although I've not had it happen to me, I am aware that the problem of liners coming loose rather illustrates my point!

However, I agree about the inherent cooling design of Lambrettas being ‘improvable’ & I’m probably not alone in the anticipation I remain under, in keenly awaiting the day when you Post images of the modifications you have personally made.....

[Fast n Furious]

[/quote]
However, I agree about the inherent cooling design of Lambrettas being ‘improvable’ & I’m probably not alone in the anticipation I remain under, in keenly awaiting the day when you Post images of the modifications you have personally made.....[/quote]

I ought to pull mine down for full inspection as it now has over 2500 miles on it since its commission last August but I'm enjoying the thrash too much (when it's not raining) and so I will tempt providence and wait until this coming winter when I intend to document and publish the rebuild, Warts n'all. Unlike the racing world, all published mods for road bikes are only worth what can be backed up with endurance mileage. I would consider it irresponsible to make suggestions that came without some degree of verification.

[Warkton Tornado No.1]

However, I agree about the inherent cooling design of Lambrettas being ‘improvable’ & I’m probably not alone in the anticipation I remain under, in keenly awaiting the day when you Post images of the modifications you have personally made.....[/quote]

I ought to pull mine down for full inspection as it now has over 2500 miles on it since its commission last August but I'm enjoying the thrash too much (when it's not raining) and so I will tempt providence and wait until this coming winter when I intend to document and publish the rebuild, Warts n'all. Unlike the racing world, all published mods for road bikes are only worth what can be backed up with endurance mileage. I would consider it irresponsible to make suggestions that came without some degree of verification.[/quote]

I don't doubt that @ all In fact, I think that your comments demonstrate a wealth of knowledge & experience as we have a common aim to help in sharing our hard earned know-how. Much of mine may have been track biased but that is an area where reliability & a methodical approach is no less important than a well set up road machine.

Variation is one of the attractions of most things in life & I remain intrigued by the fact that Lambretta upgrading continues to advance, in particular within some of the constraints that some of us self impose. A prime example is that I never imagined I would advocate air filtration on a tuned road bike, but simply the mess avoidance made me reconsider!

The fact that the only ‘cheats’ with my current road bike are a Rapido barrel, the VHB modified to take PHBH internals to make it more ‘two stroke’, nylon lined cables, modern tyres & sintered pads are the only concession toward achieving a dream bike circa 1970’s.

Whenever I get to do my Italian GP, I reason that I might allow further compromise with electronic ignition! Besides which, I’m not in a position financially to buy into state of the art complete engine builds that deliver 40bhp utilising purpose built crankcases. However, ‘home brew’ tuning (such as Holty is doing with his Rotax barrelled project is fascinating) & I wouldn’t take too much convincing to do something similar, albeit with an air cooled barrel, preferably without crankcase induction.

[Fast n Furious]

That's the thing with Lambretta!
Take a modern motorcycle...... As good as they are, you would be heralded a god with very deep pockets if you could just make it 5% better.
With a Lamby, you can make a significant improvement, on a continuous basis for very little money by comparison.
The trick of course, is being able to balance out all the improvements, so they all work in harmony with each other. Look after the weakest link and everything else will be just peachy.