Hi Comp Cylinder Heads for 2T and 3T engines

[Guest]

Can anyone help. Many years ago when I had quite a pile of Villiers twin 2T and 3T cylinder heads I noticed that there were two types. A standard head with a fairly large combustion recess and another with a much smaller recess. In discussions with Bert Greeves in 1984 he said that they used Hi Comp heads on his twin engine bikes but I can't remember if he was referring to road bikes or experimental twin engine scramblers.

The difference in size of the recess is very noticeable. Has anyone else come across any of these heads and can confirm where they were used.

Keith

[John Pattinson]

3t heads

Yes Keith they were fitted on my 32DC, I found some low comp ones in better nick and fitted them. Not much difference but I think it ran a bit cooler...John P.

[Guest]

Hi Comp heads

Yes Keith they were fitted on my 32DC, I found some low comp ones in better nick and fitted them. Not much difference but I think it ran a bit cooler...John P.

Thanks John, I was worrying that my old memory was playing tricks. Now I need to know if Greeves fitted them to DCs as I think they did. Bert would want his bikes to have an edge.

Thanks, Keith

PS ... I know they fitted modified silencer baffles. These had extra holes alongside the existing holes. Made then louder and a bit more free flowing.

[Colin Sparrow]

Are the standard ones hemispherical? I ask because my son recently came across a pair of Villiers twin heads and they had sort of half egg-shaped chambers. Could they be the high-comp type?

[Guest]

Hi Comp Heads

Are the standard ones hemispherical? I ask because my son recently came across a pair of Villiers twin heads and they had sort of half egg-shaped chambers. Could they be the high-comp type?

The 2T and 3T heads were all the same in shape. A sort of half egg shaped recess. It was the 4T that had the circular recess. The one with the smaller recess, it was about 1/4" shorter should be the Hi Comp version.

Keith

[Colin Sparrow]

Certainly Greeves did do a mild tune-up on the 2T engined bikes, and did specify a higher compression ratio than standard.

The comp ratios specified by Greeves were 10:1 for the 2T, 8.68:1 (1959-1961) for the 3T, 8.86:1 (1962-on) for the 3T.

Maybe they did use high compression heads, at least on the 2T. Alternatively they may have just mildly skimmed standard heads?

Never stop learning, do you? Thanks Keith. No way of knowing what my son has then, without something to compare them to.

The heads are for sale if anyone wants them.

[John Wakefield]

Thing is are the stud centres different on the 3T heads if not & they are the same as the 2T then it may just be that you have 2T & 3T heads. Or 2T high & low compression ones. Of course they could have been 'skimmed', thats what we did back then to try and get a bit more out of the bike. Trouble is these 'modified' bits are coming out of sheds.

[John Pattinson]

3t heads

Hole centres same for 2T and 3T...John P.

[Guest]

Hi Comp heads

Certainly Greeves did do a mild tune-up on the 2T engined bikes, and did specify a higher compression ratio than standard.

The comp ratios specified by Greeves were 10:1 for the 2T, 8.68:1 (1959-1961) for the 3T, 8.86:1 (1962-on) for the 3T.

Maybe they did use high compression heads, at least on the 2T. Alternatively they may have just mildly skimmed standard heads?

Never stop learning, do you? Thanks Keith. No way of knowing what my son has then, without something to compare them to.

The heads are for sale if anyone wants them.

Defo not skimmed. They are noticeably different in size but the same shape. So Bert WAS talking about the road bikes. I suspect that it was the DC and after models. These were genuine Villiers items.

Keith

[Guest]

Hi Comp heads

More confusion .. the 1961 Villiers 2T and 3T manual (grey cover) states ...

8.2:1 Comp 2T and 7.25:1 3T

Need to check for comparison with previous Villiers manuals.

I thought I saw a light at the end of the tunnel but it was someone with a torch bringing me more work!!! Lol

[Guest]

Hi Comp heads

It gets more confusing.

The earlier 2T/3T manual quotes cylinder heads as B9292/1 and B9292 for 2T and 3T.
The 1961 2t/3T manual quotes B12081 and B12082 for both 2T and 3T.
But I must correct my previous mail. Those comp ratios quoted in the 1961 manual are actually LOWER than the earlier specs.
Maybe Villiers dropped the comp ratios to stop detonation and improve longevity. But Bert put the earlier Hi Comp heads back on.

What we need is a precise spec for 222D engines (the 1961 32DC).

Still in the tunnel .... who has all the original Villiers production spec sheets?

Keith

[John Wakefield]

You could try John Wood via this web site http://www.villiers.info/
Other than that Villiers Services http://villiersservices.co.uk/ or Rob Carrick the author of Villiers Everybodies Engine.
Of course you could measure the capacity of the combustion chambers with graduated pipet, do a bit of maths (that will tax the old brain a bit Keith) & work out what the compression ratio is.

[John Wakefield]

More confusion .. the 1961 Villiers 2T and 3T manual (grey cover) states ...

8.2:1 Comp 2T and 7.25:1 3T

Need to check for comparison with previous Villiers manuals.

I thought I saw a light at the end of the tunnel but it was someone with a torch bringing me more work!!! Lol

Villiers Singles & Twins by Bacon confirm 8.2:1 for 2T (1956-68) & 7.25:1 for 3T (1958-64) No other variations quoted. Just to complete the twins the 4T (1963-67) was 8.75:1 Note these would be theoretical comp ratios based on swept volume, but in a two stroke compression only starts after the exhaust & transfer ports have closed, so in practice the ratios would be much lower.

[Colin Sparrow]

The 10:1 compression ratio I quoted for the 2T as fitted to the 25DC came from the Greeves sales brochure...

[John Wakefield]

The 10:1 compression ratio I quoted for the 2T as fitted to the 25DC came from the Greeves sales brochure...

According to Practical British Lightweight Motorcycles by Steve Wilson, the 1961 Norman B4 Sports also had a "tuned 10:1 compression ratio (2T) engine"