Sleeving and piston fit for a VB

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Mike Nash
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Sleeving and piston fit for a VB

Postby Mike Nash » Tue Jun 30, 2020 7:17 pm

Greetings Comrades!

I need your advice please. I've decided to fit my beautiful Hepolite standard sized piston to my best VB barrel, an action which will require the latter to be sleeved. The piston with its three compression rings (and no scraper) is in the bottom picture. It's marked inside on one side as "HEPOLITE 5631-" and on the other it has "W A" with the figures "243" beneath them. The upper picture is a close up of the relieved side which shows some pits which I suppose indicates it to be a sand casting. Measuring the across the bottom of the skirt parallel to the gudgeon pin I get 86.05 mm and perpendicular to the pin its 86.2 mm, a difference of 6 thousands of an inch. (The top of the piston is 85.54 mm.)

My first question is who would you recommend to do this work? I live in the NW Hampshire UK so anyone in the south of England is in range. I've had good work done by Saunders at Southampton on Morris Minor heads but air cooled side valves are a bit peculiar and rather rare today and they a need a special understanding on clearances. That the hot exhaust zone can cause a bulge in to the bore and that the whole barrel can go banana shaped is not often appreciated.

Secondly, I'd need your advice for clearances for this solid skirt piston. I suppose these are also rather rare now and suspect most machine shops are more familiar with split skirt rather than solid. I'm hoping, of course, to find someone who understands these things but your advice is still valuable if only so I can go along as an "intelligent customer"!

Regards from MikeN.
PS The piston (with rings) weighs 481g and the pin, which has interior tapers, is 95g. (To these must be added the circlips.)
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nevhunter
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Re: Sleeving and piston fit for a VB

Postby nevhunter » Wed Jul 01, 2020 12:32 am

Sidevalve barrells warp as you note. it also make a sleeve a less favoured solution because of the distortion. In the reco Industry it was always procedure to allow an extra .001' One thou of an inch for reduced rate of heat transfer of the sleeve to the cylinder . The 006" inch ovality is about right.It will also have some taper. AS for the running clearance don't be too miserable, especially if it's pulling a chair. Plenty of good sidevalves have been spoiled by running too tight a piston fit. Nev

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Bob.Murphy
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Re: Sleeving and piston fit for a VB

Postby Bob.Murphy » Wed Jul 01, 2020 9:54 am

Hi,
I had a '31 Panther 500 barrel sleeved by:

T&L Engineering (Bedford) Ltd.
Pear Tree Farm,
Wilstead Road,
Elstow,
Beds,
MK42 9YG.
Tel: 01234 352418

They did a good job but as the bike restoration is still 'work in progress' I can't claim that it works !
This was back in June 2014 so the Co. may have changed. Might be worth giving them a call as they seemed to be 'old school' and knew about bore ovality and piston clearances. I supplied the brand-new standard piston I got from Thorntons and I believe T&L discussed the job with Thorntons.

The Panther is an OHV of course so different cooling/distortion issues to your job.

I seized my '57 'VB' back in 1972 and got a replacement piston from Jim Lee who dealt with AOMCC Spares at the time. It was a solid skirt job and was forever nipping-up on hills, I should have had the barrel honed at the time but I was young and broke !

If I knew then what I know now . . .

Bob.
My avatar shows the late Len Rich in 1970 with the bike I now have - a 1958 Ariel VH

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Re: Sleeving and piston fit for a VB

Postby john.whiting » Wed Jul 01, 2020 11:37 pm

The piston in the pics has the small divots above the pin bore that are typical of cast in expansion controll inserts......might be worth checking if it has the inserts......The strangest seizure I ever saw was caused by tadpoles !

Mike Nash
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Re: Sleeving and piston fit for a VB

Postby Mike Nash » Thu Jul 02, 2020 1:02 pm

Thanks for the advice, friends!

Bob, I'll chase up T&L but I'm hoping I'll be lucky enough to find someone closer to home - but who knows? I'll report on what happens.

Thanks Nev! I knew I could rely on you! I'm also wary of the heat transfer of sleeving but I fear it'll have to be done. On sidevalves, I've learned to follow Hartley's dictum of "run as rich as possible without loss of power" to stop things getting too hot. However, I fear the hottest conditions these days may be in stop-start traffic on motorways where you can't shut the engine off and don't have enough speed to give a proper cooling airflow. (You get a really hot right calf!) Probably not a condition I'm likely to meet these days. But regarding clearances, where am I with a piston that's just under three and a half inches across in a sleeve? Somewhere I've read from yourself and David Anderson that 5-6 thou was about right unsleeved but I can't find the reference and am not keen on relying on my memory.

To John, I've given the piston a good staring at and the "divots" above the pin are holes that go downward to the upper part of the gudgeon pin bearing each side in the piston, so it's got 3 holes for lubrication each side, two at the top and the usual one beneath. "Tadpoles" are the name of the inserts to make these holes, are they? Not heard that before! Anyway, the holes are nice and clear.

Thanks for all your help, MikeN.

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Steven.Carter
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Re: Sleeving and piston fit for a VB

Postby Steven.Carter » Thu Jul 02, 2020 4:05 pm

How about, they've done some stuff for me and have been just fine

OCS

Owlesbury Crankshaft Service
Unit 12 Winnall Valley Road
Winnall
Winchester
SO23 0LD

Telephone : 01962 855969
Fax : 01962 856969

Mike Nash
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Re: Sleeving and piston fit for a VB

Postby Mike Nash » Thu Jul 02, 2020 10:12 pm

Thanks for that, Steve!
They're only 20 miles from me and I'd forgotten all about them.
MikeN.

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Re: Sleeving and piston fit for a VB

Postby nevhunter » Fri Jul 03, 2020 12:39 am

A solid piston needs more clearance than a T slotted one It has no "give" and the T slot and "W" slot use a difference of temp from piston crown to skirt that acts to reduce expansion of the skirt using it's ovality. They work better in liquid cooled motors where the bore stays cooler.
In that motor with a bore that size 6 thou will NOT do it. I've put that in 3 inch bore sidevalves and it's not enough. Nipping up causes damage often and you can't keep taking more metal out to remove bore damage as it's weakening the whole thing. You must check what thickness of barrell at the bottom remains as the sleeve does very little to keep it from separating.I've seen plenty lift the barrell off because the parent casting has become too thin. The sidevalve heat problem is because it has too large a combustion chamber area and the exhaust port is stuck on one side causing the distortion in that area. You can also get carbon UNDER that section of the sleeve. I really DON'T recommend sleeving SV's if you can avoid it. I'm not as keen as I was once on sleeving anything. Many cylinders don't have enough metal in the walls to safely sleeve them. Nev

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Re: Sleeving and piston fit for a VB

Postby john.whiting » Fri Jul 03, 2020 2:03 am

MN...nope,tadpoles were in a bucket of ditchwater used to refill the radiator......blocked all the tubes ,and smelled like boiled chicken......for a day or so ,until they began to stink.

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Re: Sleeving and piston fit for a VB

Postby Mike Nash » Fri Jul 03, 2020 8:43 pm

Nev,
Last night I went out and turned my two VB barrels over and they seemed to me to have very little meat to fit a sleeve into. So after reading your note I've used calipers and a steel rule (repeated several times) to reach over the base flange and I find that for one barrel (bore 88.5 mm) the wall below the fins opposite the valves is 3 mm thick, forward its 3 mm and astern its 3.5 mm thick. For other barrel (bore 87.5 mm) opposite the valves its 6 mm thick, ahead its 5 mm and astern its 4 mm thick.
This thinness has come as a big surprise and I think I should change course and look for a piston that fits the thickest walled barrel rather than sleeve either barrel to my piston. What do you think? How thin can a barrel be and survive?

And to John re the tadpoles, I thought I'd just learnt a new bit of Oz slang! Didn't think you meant REAL tadpoles.
Regards and thanks to you all, MikeN.


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