Re-Build problems.

[Steamdriven]

Hi folks,I'm looking for a bit of advice (re-assurance) about a Villiers(ish) based engine I'm building.
Using a re-lined MDS barrel and head fitted onto a set of Alpha crankcases with a narrow Alpha crank (No flywheel provision......battery,coil ignition.)
My problem is that when assembled the larger Alpha crank flywheels foul the piston skirts. I relieved the piston skirts,rounding off piston skirt corners but removing no overall piston length (really close though).
It gets worse,on assembly I was expecting to jack the cylinder up,however at BDC the piston crown is.100" (2.55mm below exhaust port and .235" (6.0) below liner top.
i'm thinking that the best thing to do is to machine metal off of the top of the crankcases (.100"+) where they connect with the barrel.
I know that whilst doing this the piston skirts will foul again and will need clearance,also base of barrel liner will need reducing the same amount to clear crank flywheels.Doing this will reduce overall piston (Nametab) length by .100"+.
I expect this will account for faster piston/bore wear,but is it completely out of order?
Am I going the right way????,
Advice would be appreciated.
(By the way, the problem is caused by Alpha leaving more metal (thicker) on the top of their C/cases compared to Villiers).

[johnrunnacles]

Sounds to me like you may have the shorter Con-rod fitted to your crank, Steamdriven. It might account for all of the piston discrepancies you have described.

[Steamdriven]

Hi John, I've measured once (and again,and againnnnnnn).
The stroke is the right length,but if you measure from the centre of the crank to the top of the c/cases the Alpha ones are .100" higher than my villiers ones, which is raising the barrel. Rod 5 1/2"".
I don't know if I've got some crankcases out of Alpha's scrap bin?

[johnrunnacles]

Rod is the right one, then Steamdriven. Surprised that 1/10th inch at the base makes the difference it does at the liner top ............. but perhaps I shouldn't be?

Good luck with sorting it

JR

[Floydism]

I may have gotten the wrong end of the stick (not the first time!) but machining a hundred thou off the cases would leave the piston skirts in exactly the same place. if the pistons clear now, they will still clear later.

[teamferret]

piston fouling not an issue. I've recently had to machine some villiers engine cases down, the maximum I could take off was 4mm. After that the transfer ports start to fan out and leave little top face left for sealing. Why not remove material from the barrel, though again the transfer ports limit the amount. Maybe have to do both???

[johnrunnacles]

Just another thought, Steamdriven, but have you measured the piston, in particular the distance the gudgeon pin is set from the crown? Some Vale Onslow pattern pistons have emerged recently. These put the gudgeon pin closer to the crown of the piston than do standard Villiers pattern ones. I don't have a measurement for the difference but it might (?) account for the kind of discrepancies you have recorded for position of the piston crown in the bore. Visual giveaway for a V/O piston is (usually) the domed crown.

Floydism is right, by the way.

Incidentally, if anyone is looking for a Vale Onslow pattern piston, they are currently on offer on eBay by Peter Vale-Onslow.

JR

[IanCordes]

Re Vale Onslow pistons, Steve at VS told me a little while back he has loads of them; all std bore though.

Ian C

[John Wakefield]

Just another thought, Steamdriven, but have you measured the piston, in particular the distance the gudgeon pin is set from the crown? Some Vale Onslow pattern pistons have emerged recently. These put the gudgeon pin closer to the crown of the piston than do standard Villiers pattern ones. I don't have a measurement for the difference but it might (?) account for the kind of discrepancies you have recorded for position of the piston crown in the bore. Visual giveaway for a V/O piston is (usually) the domed crown.

Floydism is right, by the way.

Incidentally, if anyone is looking for a Vale Onslow pattern piston, they are currently on offer on eBay by Peter Vale-Onslow.

JR

£100 each standard size only https://www.ebay.co.uk/itm/Vale-Onsl...8AAOSwsb9exmMR looking at all the other stuff he is selling he is cashing in his pension fund

[johnrunnacles]

Apologies for having taken your thread "off-piste", Steamdriven.

Take care, and good luck with sorting the problem with the engine. Let us know how you get on.

John R