VG barrel/piston/conrod query

Singles, twins and fours.
Dave.Thomas
Holder of a Waxed Cotton Anorak
Holder of a Waxed Cotton Anorak
Posts: 317
Joined: Tue Sep 06, 2011 9:40 pm
Location: Birmingham, England
Contact:

VG barrel/piston/conrod query

Postby Dave.Thomas » Wed Jul 11, 2018 11:25 pm

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

User avatar
adrie.degraaff
Holder of a Golden Anorak
Holder of a Golden Anorak
Posts: 2865
Joined: Sun Feb 27, 2011 10:07 am
Location: Holland
Contact:

Re: VG barrel/piston/conrod query

Postby adrie.degraaff » Thu Jul 12, 2018 6:02 am

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
Holder of a Waxed Cotton Anorak
Holder of a Waxed Cotton Anorak
Posts: 317
Joined: Tue Sep 06, 2011 9:40 pm
Location: Birmingham, England
Contact:

Re: VG barrel/piston/conrod query

Postby Dave.Thomas » Thu Jul 12, 2018 7:05 am

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

User avatar
adrie.degraaff
Holder of a Golden Anorak
Holder of a Golden Anorak
Posts: 2865
Joined: Sun Feb 27, 2011 10:07 am
Location: Holland
Contact:

Re: VG barrel/piston/conrod query

Postby adrie.degraaff » Thu Jul 12, 2018 8:05 am

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
Holder of a Waxed Cotton Anorak
Holder of a Waxed Cotton Anorak
Posts: 317
Joined: Tue Sep 06, 2011 9:40 pm
Location: Birmingham, England
Contact:

Re: VG barrel/piston/conrod query

Postby Dave.Thomas » Thu Jul 12, 2018 8:47 am

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

User avatar
dave.owen
Holder of a Golden Anorak
Holder of a Golden Anorak
Posts: 1196
Joined: Wed Mar 23, 2011 10:05 pm
Location: swindon
Contact:

Re: VG barrel/piston/conrod query

Postby dave.owen » Thu Jul 12, 2018 8:50 am

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

Dave.Thomas
Holder of a Waxed Cotton Anorak
Holder of a Waxed Cotton Anorak
Posts: 317
Joined: Tue Sep 06, 2011 9:40 pm
Location: Birmingham, England
Contact:

Re: VG barrel/piston/conrod query

Postby Dave.Thomas » Thu Jul 12, 2018 9:19 am

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

User avatar
dave.owen
Holder of a Golden Anorak
Holder of a Golden Anorak
Posts: 1196
Joined: Wed Mar 23, 2011 10:05 pm
Location: swindon
Contact:

Re: VG barrel/piston/conrod query

Postby dave.owen » Thu Jul 12, 2018 9:27 am

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

Dave
AOMCC Treasurer

Dave.Thomas
Holder of a Waxed Cotton Anorak
Holder of a Waxed Cotton Anorak
Posts: 317
Joined: Tue Sep 06, 2011 9:40 pm
Location: Birmingham, England
Contact:

Re: VG barrel/piston/conrod query

Postby Dave.Thomas » Thu Jul 12, 2018 9:41 am

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

Dave.Thomas
Holder of a Waxed Cotton Anorak
Holder of a Waxed Cotton Anorak
Posts: 317
Joined: Tue Sep 06, 2011 9:40 pm
Location: Birmingham, England
Contact:

Re: VG barrel/piston/conrod query

Postby Dave.Thomas » Thu Jul 12, 2018 9:50 am

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


Return to “Four stroke”

Who is online

Users browsing this forum: No registered users and 4 guests