More questions than answers

[Rick Hughes]

This 1938 vh 500 engine is testing me at every turn
Iv not had her running running since I bought her
I couldn't work out how the valve lifter worked until I saw a picture of a normal rocker mine had been cut down and polished till it resembles chrome and no flat on it for the lifter ( which was blanked off ) which i manged to buy
The compression seemed very high when kicking it
So I stripped the top end off tonight
It had a specialalloid standard piston in. I cant guess what its out of the bore when measured with a tape measure was 83.5. The
The sprockets under the primary drive case were 22t and 39t. Which doesn't seem normal it had a huge amal carb
A 2mm compression plate. The conrod is very shiny like the rockets
Ill get there its a steep learning curve having never worked on a British bike

[tony.barnett]

I think your bike has been modified quite a bit.

[Rick Hughes]

Im unsure where to go to perhaps lower the compression can compression plates be bought somewhere or do I have to make some and how thick can I make them
Does a extra mil make much difference
I took the barrel of to get some answers. But it gave me more questions.
Im going to put the top end in a box and visit someone near me that seems to have a lot of ariel knowledge and parts.

[tony.barnett]

So, its not normal for a 38 VH to have polished rockers or a polished conrod. Standard bore would be 81.8mm, so yours has been enlarged. The 2mm compression plate is also not standard - perhaps used to give valve clearance on the non-standard piston or control the compression ratio. A standard carb would be an Amal 89 or 289 which is, I think 1 1/8" bore.

So - far from standard...but...I'd think it would go well if you get it all sorted. I'd be interested to see what cam it has.

Has it got any history?

[Rick Hughes]

No history at all. My friend bought it off a chap and didnt ask anything. He cant find his number. The other guy said if had been hill climbed all good while ago at Haughton towers and the chap rode it there
I might look at the cam as well
Id like it as near to standard as I can afford.
Im.hoping put a standard cam in it if its not. Raising the barrel a little bit more if the pushrods and tubes stand it
A amal concentric carb. For now

[nevhunter]

I'm not sure I'd rush to detune it unless its set up to run on alcohol. Check the valve springs are not too strong. The VH ones tend to be and that is hard on the cams Not required unless you want to Rev the Guts out of it. You can check the Cam lift by checking the Valve lift against stand OR the Push rod lift. I'd replace the Front rocker and set up the valve lifter again. It's good to Have when starting, Forget about Polishing the replacement. The rocker box Gaskets are THICK originally. Your motor may/will have Polished ports and Maybe enlarged (INLET) Valves If it breathes well it will want to go and will NEED a bigger carb than standard. Make sure the current Muffles doesn't apply much Back pressure, A domed piston gets hotter (more area) and needs more advance. Maybe some metal can be taken off the Crown but don't make it too thin.. I don't like the idea of compression Plates as it Makes sealing the cover tubes more difficult and doesn't locate as well and makes the engine higher, and there's not a lot of room there in the first place. Is it single Port? Have fun, A bit of extra Power wont bother you, After all they were called the Poor Mans JAP. Nev

[david.anderson]

A standard hot up in Australia was to remove 1/8” from the cylinder base flange to increase compression ratio, so it is possible that the compression plate is there to restore or partly restore standard compression. The VH cylinder base flange is 1” thick so if it is less, that will be the reason for the compression plate.
1/8” increases the 6.8 piston to about 8.1 to 1, and the 7.5 piston to about 9.6 to 1. In both cases there is no problem with the valve hitting the piston with a standard cam lift.
If the carb is fitted direct to the head then the largest concentric carb that it could be is a 32mm (1.25”) which is only 1/8” oversize and not a problem on a VH.
Are you certain the clutch wheel has 39 teeth and not 40 teeth.
David

[nevhunter]

The gudgeon Pin with the OHV singles Piston is very close to the Oil Ring Land so Not Many (Other Brand) Pistons can fit. A 1/4 inch shorter conrod would help and If you want to remove Metal from the Base flange( there's plenty of thickness) reduce the length of the conrod a Bit more. You are also reducing weight. . David I've found a NEW VH rod if you are interested. Nev

[Rick Hughes]

I think the cam is standard but id like confirmation before I put it all back and have a go at timing it etc
Iv never heard it run yet

[paul.jameson]

We will need an end on view of the cam lobes to be able to identify it. You may find it has a number stamped on the end, such as A6/664, A7/642 or F. Whilst telling us that number may help, it won't if the cam has been modified but we might be able to tell if it has had extreme modification.