Silverstone Pistons

[tonyed27]

Are there any alternatives, or indeed genuine, pistons on the market for the Greeves Silverstone?

[Dogsbody]

Std or oversize?

[Stan Nicholson]

I have been using the forged pistons from Villiers Services for years now. Available in Std and over sizes that take the motor over the 250cc limit. Not that is a problem for me as our club allows up to 5% oversize . Also fitted with 1mm thick rings which is an advantage for reducing ring flutter.

Haven't seen any original Dyke top ringed, Hepolite pistons for ages.

[tonyed27]

I can see 66mm pistons forged at ?105 for 66mm bore in std and o/s. Mine's +0.030 at present, which of course they do not do, but I can o/s to +0.040 take it out to 254cc.
The engine on mine was overhauled during the mid 70s and hasn't run since. The piston is a new original dykes ringed Hepolite which requires some heat cycles on it to break it in.
What about crank parts? The parts lists has separate entries for the main bearing components rather than listing a complete bearing number.
Can anyone recommend a sealer for the GRP fuel tank to protect it against ethanol.

If I can help any member with Yamaha TZ parts, discounts to member of the GRA.

https://rhsyamahabitz.com/

Thanks gents

[John Wakefield]

As far as petrol tank is concerned Tony, as its already had petroil in it it will have impregnated into the fibreglass so sealer will not adhere, In fact the sealer could come away and then start blocking fuel lines. Best plan is to fit a replica alloy tank. The alternative is to use av gas and frankly in a high comp engine such as a Silverstone that surely would be the best fuel to use as its 100 octane and contains no Ethanol

[tonyed27]

I've had the tank full of MEK for the past two weeks and drained it off this morning. Did a colour check with a filter paper against afresh sample and it's clear.
The tank has been empty since the mid seventies and even before the MEK soak felt completely clean, almost like it's never been used, although I suspect it has, so I think a sealer will work.
There aren't any alloy tanks on the market although Tony at Holtworks does them for the off roaders. I have to have chat to see if he'll make them, I used to work with him at Marshall Aerospace.
I see there was another mid 2021 thread about alloy tanks from TAB, but they don't list any. I might try Alf Mossell as well.

[John Wakefield]

Tony I still dont think sealers will work well with fibreglass. Re alloy tanks Gary Bamford may be able to help. Bob Horton who was mentioned in this thread https://www.greeves-riders.org.uk/fo...85-alloy-tanks died in April 2015 so not available from him anymore.

[tonyed27]

Providing they are epoxy based which some are they should be ideal to seal GRP. The ones designed solely for metal tanks I think would be unsuitable. I will try at any rate. On my own head be it.
The alternative is Avgas and working for an aerospace company which has its' own airport it should be easy to obtain. Don't you believe it.

[IanCordes]

Local flying clubs are usually accommodating, where Avgas supplies are concerned. Simplest solution, I would have thought, as you need high octane fuel for the Silverstone anyway. It also has the benefit of lasting waaay longer than pump ethanol fuel.

[Stan Nicholson]

RE the aluminium tanks, in the thread you mention from Aug - Dec 21, TAB did make 3 Silverstone replica tanks at that time, so I assume they still have the patterns. Presumable they would want more than the price quoted when making 3, but might be worth contacting them for a 1off price.

I always believed that Avgas was formulated to work at high altitudes and wasn't that good for ground level use. Something about being slow burning?

As I have been racing my Silverstone pre ethanol in pump gas, I use race gas now, currently VIP C12 but at about $200 a drum (5 US gallons, 18.9 litres) this is double the price of a couple of years ago. But, hey, who said racing was cheap .

[Stan Nicholson]

If your +.030" Hepolite piston is new, is the bore still OK? Would a light hone clean it up if there is no/little wear in the bore?

The main bearings you mention would be the alloy cages and separate rollers running directly on the crank? I have never changed these in all the years I have been racing my Silverstone but figured it would only be the rollers that would need replacing if there was any clearance.

Not sure if your RES with the new electronic ignition is still fitted with the heavy steel spacer between the timing side main and the oil seal fitted in the ignition adaptor plate, but I was having constant problems keeping the oil seal lip lubricated and was changing this every couple of races as the lip overheated. Changed to a different material seal but that only partially helped. I then measured the diameter of the centre of the gap between the outer diameter of the alloy cage and the inside diameter of the outer race in the crankcase and drilled and chamfered a series of holes, equi-spaced on this pitch diameter in the steel spacer. Problem solved as the seal now gets copious lubrication from the petroil (20:1 Castrol R in my case).

[IanCordes]

Stan. 'I always believed that Avgas was formulated to work at high altitudes and wasn't that good for ground level use. Something about being slow burning?'
I believe that is correct, although 'wasn't that good at ground level' may be overstating it. When I was racing 250 2-strokes (MZ) the thinking was to use around 50% 100 octane Avgas and 50% super-unleaded ethanol-free 98-99 octane pump fuel; still available in some parts of the country from Esso; which balanced everything up. However, there are currently members who use Avgas exclusively. Maybe their machines are not put to the rigours they were back in the day, but no problems reported.

What use are you planning to put your Silverstone to, Tony?

Ian C.

[tonyed27]

Avgas or 100LL as it is now known is fine at all altitudes. Some dilute it with pump fuel but I used it in my TZs back when as well as the 100 octane pump fuel we used to get when the planet was new.
The bore with the plus 0.030" piston is a rebore, I can still see the hone marks.
As for its' use, well I am not going to be racing it as with the abundance of past spinal injuries I don't want to finish up in a wheel chair, my cat would be well displeased. So it will be the odd parade and shows. I bought it because I always liked my old Silverstone and as far as I am concerned it it as iconic as the 74 TZ I have.
Demon Tweaks do a 99 octane long life non-ethanol race fuel so I may go down that route or run it on 50 year old single malt whiskey which is cheaper than many of the race fuels on sale.

[Dogsbody]

I have sealed a Silverstone tank successfully with Caswell, many sealers do not work on fibreglass. I only use Sunoco race fuel , 101 leaded no ethanol and available either delivered or at race circuits when there are supported car race meetings on. Usually get it a Oulton Park , pumped into my container, cheaper than drum price. See Anglo American Oil website.

https://aaoil.co.uk/

[anglian man]

I have used Caswell on several Greeves tanks with good results, presently I use Wagner , ok for plastic and fibre-glass tanks, just use 105 octane ethanol free (3-5 yrs shelf life ) from shows or race tracks in all my bikes