VG barrel/piston/conrod query

[Dave.Thomas]

Hi, building a ‘48 ish 500 single with parts from a variety of sources. Crank is VG with the rod (A7/524), also found in VB’s. Apparently this is longer than the VH rod ? I have assembled it with a new VH piston, but the piston protrudes above the barrel around 3mm at at TDC. Did the VG have a shorter crown height piston ? Can’t find anything to differentiate them in the Drags tech pages, they recommend the same piston for VG and VH.
My barrel could have been shortened but I don’t think so, the base flange is 23mm thick, from the base surface to head surface is 134mm, and from base to top of spigot is 137.5mm. I can easily make a Packer for under the barrel but I’m curious to know where the extra 3mm is from ?
Thanks

[adrie.degraaff]

The VB rod is longer (and heavyer) so you need to find a VG rod.

You could opt for the stronger a VH crank and rod.

[Dave.Thomas]

According to the Drags info charts, the A7/524 rod was used in both VG and VB ?

[adrie.degraaff]

That should be VG and VA.

A VG rod is aprox. 190mm centers and a VG crankpin is lining with the brass crankcase cambaring, when the pin is higher you have a VB crank in it.

[Dave.Thomas]

Thanks Adrie. I have to deal with it as it is, I have just had the big end replaced in the rod/crank

[dave.owen]

I have 2 spare VG cranks, both have A7/524 conrods
Dave

[Dave.Thomas]

Thanks Dave, maybe mine is the correct rod then ? Do t suppose you have a VG piston that could be measured ?

[dave.owen]

I run both my VG and VH on the same pistons. Both barrels are the same. 24 mm base flange.

Dave

[Dave.Thomas]

Thanks again. Maybe my barrel has been shortened? Does anyone have an iron 500 barrel they could measure please ?

[Dave.Thomas]

Just measured an NH barrel, it is 10mm shorter than this VG one, which is what you would expect ? The mystery continues