Thought I'd start a new thread - just in case I'm daft enough (at my age) to start a new project
Already mentioned in cylinder head? post, so here's an update:
Lot of things to consider before actually deciding to commit funds and 'go for it'. The cylinder head being the first.
After much on-line searching I cannot find, considering suitability and availability, a better option than Enfield. But, like most things to do with engineering, a compromise is required. In this case, my aim is for an engine of around 750 / 800cc - which is where the first conundrum arises: the Enfield 350 has a veteran-era bore / stroke of 70/90. I couldn't accept that - I prefer square or over-square. 78 x 78 gives near 350cc, but a bore of that size would be a mis-match with Enfield's 350 head, insomuch as the head bolts would be perilously close to the CI liner in my alloy barrel - if not colliding with it! So a 500 head (with more appropriate ports & valves) is required.
But wait - a 78mm bore is way under the 500's 84mm bore. Will that mean the combustion chamber overlaps the cylinder - or the inlet valve hits the cylinder (as is the case with BMC 'A' series engines when modified). I won't know until I can get my hands on a 500 head (hopefully soon). And will the head gasket adequately seat on the liner without stressing the flange?
Also, it looks like I'll need to make a gasket to suit, reminding me that was actually the greatest problem I had to solve with my last vee. Try as I might, I couldn't get the fire ring to compress the variety of materials I tried. I figured what was needed was a material that compressed when the fire ring was applied, but not so compressible that it would fail in service. Found a firm (major gasket manufacturer) who confirmed my analysis - but they don't supply raw materials to the public! Soon after my enquiry to that firm. I received a parcel containing supplies of that material - together with a note "you don't know where you got this from"!
So I've been trying to compromise on bore / stroke dimensions. And here piston selection come in (I refuse to make cylinder heads or conrods and seek to avoid making pistons if at all possible). So what's available piston-wise in the 78 - 80mm region? Not a lot, it seems. There's a Ford Mondeo piston @ 83mm, but that'd mean a stroke of 70mm or less. OK, my last vee is 92/75 but that was designed for racing. I now want a more moderate engine - heavier flywheels, nearer square bore / stroke etc. And so ages were spent investigating on-line.
There's a Commando piston avail by Wiseco at 80mm, but at eye-watering price. Same with KTM and others. Then I discovered a Vauxhall piston at 79mm. And at a reasonable price (considering this - if it goes ahead - will be a prototype and could well end up scrapped if major problems arise). And so that is another item 'parked' for now.
But what about conrods?
Again, much on-line searching, with little progress. If I go for 79mm bore (and complimentary stroke of 76.5mm) I will need a conrod of around 6 1/4" to clear the 7 1/2" flywheels I've figured would be a good compromise. Whether that rod has a roller or shell big-end I don't really care, but will need to know before making the crankshaft (which, because I no longer have access to heat-treatment facilities, will need to be pressed-up as opposed to one-piece).
Sadly, very little is available, mainly due to the fact car rods are quite short because they have no flywheel to avoid. The only candidate I have found so far is BSA CB/DB (the shortest of the 3 versions - ZB was the longest and BB the intermediate). A10 / A7 may be another option, but would mean another pair of new Thunder rods (am trying to keep the cost down and prefer steel anyway).
I have one CB rod, but would need another - does anyone have one they're willing to sell?
