I now have enough people on my list to order a batch of 90mm pistons...I will get in touch with those who have already contacted me during the next week regarding payment etc.
I will be requesting a non refundable deposit before placing the order...
Delivery should be approx. 3 weeks from the placement of the order...
I'll run the list for a further week (until 21-5-2018) for anyone who wants to add their name. Beyond that date it will not be possible to place an order....Ian
They are forged pistons with a modern ring set (3 piece scraper, thinner compression rings), so to a much higher spec. than the originals...
Suitable for use in a side valve with an M21 crank (112mm stroke) for 712cc or for use in the B33 OHV engines for 559cc or 600cc with a modified M20 crank fitted...
Bit of a late reply from me here Ian... Thanks for info. Since I have just gotten my M21 together the timing is kinda bad for me to start modifying. But I was interested about the prize for future mods. I may get back to you on this sometime in some distant future...
The list for pistons will close tomorrow evening, so it's the last chance if you are thinking of having one...
The order for the batch will be placed in the coming week...
Piston size for this batch will be 90.5mm, producing 720cc when fitted to an M20 with an M21 crank...566cc when fitted to a B33 with a standard 88mm stroke and 604cc when fitted to a B33 with a modified M20 crank...
Contact me off forum before Tuesday if you decide you have a requirement....I have now e mailed all those who have already requested one...Ian
Hi Bruce..The limit to the size of the piston is really governed by the width of the barrel casting just below the fins...You have to retain a half sensible wall thickness here, though the barrel is supported by the tappet chest....
I have measured a number of barrels in the past and seem to recall it could go a little bigger...You would have to check that though and satisfy yourself about where you think the limit lies...These limits can sometimes only be found by experimentation..
The location spigot at the bottom of the barrel is indeed machined completely away...My barrel and the ones on all the 720 engines I have built locate on the barrel studs only. These are a pretty good fit in the barrel and to date this method has not resulted in any problems...
After boring you will have to machine (or file with a half round file) a suitable chamfer at the bottom of the barrel to ease the entry of the piston rings..
I normally bore the barrels to a .005" skirt clearance but that does dictate proper running in procedures are followed...Personally I'm a believer in that method.
If you want to ride it hard from the outset then I would suggest you give it at least another .001"- .0015", but in that case you would be entering unknown territory and would be responsible for the results!....Ian
