99 pistons

Not 100% but I think that would = a + 80 bore on an 88?

Please correct me if I'm wrong.

I think it has been done, someone will know more. Crank re-balance maybe a compression plate under barrel ,got to be better than a re-sleeve. Phil will know. 550cc.

Have done it. No problems, no balance worries.

Hi Gordon, Did you have to shorten piston skirts?, or loose the spigots?.

No, it was just bore, fit and forget.

Avoid the slotted skirt type if possible , although I never had a problem with those.

The original 88 and 99 were fitted with the same liner machined for length and bore depending upon which engine it was going in. It was only fairly recently that dedicated liners for each model were produced. The Model 7/88 motor was fitted with a liner with a wall thickness of nearly 5mm.....and still is!!!! It will easily take a rebore up to +80" which is standard 99 piston size. Plus even another rebore up to +100".After this you might run into balance problems depending upon the choice of piston, especially if the ridiculously heavy GPM ones are used.

The only drawback of this mod is the one mentioned. ie you will end up with an engine capacity of between 525cc and 550cc. Which some insurance companies do not like hearing about. You possibly know already that Gus Khun modified stock 88 engines to have nearly-square 500cc engines by using 650 pistons in bored barrels hung on modified cranks with a stroke of around68.5cm. Apparently they were not very successful but don't know why.

If you don't tell anyone how would they ever know? I suppose they could engage Anthony as consultant ,and we would have to bribe him to keep shtumm. Sounds like a plan.Or insure it as a 600 with loads of room for reconditioning!. Now we know why the 600/650 motors broke barrels and the 88 did not.

Previously anthony_curzon wrote:

The original 88 and 99 were fitted with the same liner machined for length and bore depending upon which engine it was going in. It was only fairly recently that dedicated liners for each model were produced. The Model 7/88 motor was fitted with a liner with a wall thickness of nearly 5mm.....and still is!!!! It will easily take a rebore up to +80" which is standard 99 piston size. Plus even another rebore up to +100".After this you might run into balance problems depending upon the choice of piston, especially if the ridiculously heavy GPM ones are used.

The only drawback of this mod is the one mentioned. ie you will end up with an engine capacity of between 525cc and 550cc. Which some insurance companies do not like hearing about. You possibly know already that Gus Khun modified stock 88 engines to have nearly-square 500cc engines by using 650 pistons in bored barrels hung on modified cranks with a stroke of around68.5cm. Apparently they were not very successful but don't know why.

Good morning Anthony and Merry Christmas to you and everyone reading this - I am interested to find out a little bit more concerning these modified 88 crankshafts to which you allude. Did they start with an 88SS crankshaft and keep the 1.5 inch big-end dimension ? Do you also know what con-rods were utilised and what year were these produced ? Cheers, Howard

Does anyone seriously think that the insurers would dismantle an engine, to check it?s capacity?

If you have to declare anything to insurers, tell them that, it's a +.080" rebore using original pistons. A 68mm bore with 72.6mm stroke gives 527cc. Hardly a massive over-size.

I would want to check that the fin root diameter is the same for 500 and 600 barrels, to make absolutely sure that there is enough metal once rebored. If it's at all marginal, look at using through-studs at the sides like the 850 Commando

Paul

Previously robert_tuck wrote:

Avoid the slotted skirt type if possible , although I never had a problem with those.

Someone wrong here telling members to avoid slotted pistons this as come from Norvil and even there wrong too and I will tell you why for one these pistons are Lomax alloy piston with extra strengthbosses and expanding side skirts to control any side to side movement at high speed and give good oiling to the piston walls and these pistons are shaped so the compressionrings and oil ring does their job right and minimises shocksfrom any vibration within the engine, developedby Hepilex most car engines can be found with them installed, yours anna j