Square Head Vs. Round Head

[subira]

Dumb questions of the day coming up:

What's the benefit of the square head/barrel combination on Villiers motors, I come up with weight and better cooling, but is there anything else ?

Seems every Villiers bike tested in magazines has a different head/barrel combination so there's many different types: Parkinson, Alpha etc.

So what works best for trials motors and why ?

I remember that the 210 Karting lads used the round combo, not sure if they were alloy replicas. If anyone needed better cooling I thought it would be them.

But looking at the various James bikes tested in: Trialsworld, Classic Dirtbike and YOU HAVE USED WORDS OR A PHRASE WHICH ARE NOT PERMITTED ON THIS WEBSITE. PLEASE DELETE YOUR POST/TOPIC. DO NOT TRY TO CIRCUMVENT THE FILTERS IN PLACE ON THIS WEBSITE recently it seems that its a must have, so which variant is fitted to the bikes in those mags ?

[trialsrfun]

Hello Subira what is this then as I move from Villiers to Cub are you doing the opposite ? and by the way it is not a dumb question at all but it is one that has no easy answer. The 210 karts had to retain the outward appearance of the Villiers original hence the rounded shape but these are ported way different than a trials engine.

Greeves made the square barrel and head as well as the tapered (front to back) Challenger type and both were available in trials as well as scrambles spec, in itself this does not mean much as a head spacer can be fitted to lower the comp ratio or sometimes a thin spacer between barrel and c/cases this helps to maximise the transfer port openings.

Sometimes it just boils down to what you can get hold of and then try different settings etc but the biggest difference on a Villiers comes from a good electronic ignition, well set up carb and as long an exhaust pipe as is possible to fit. Many people Richard Thorpe included use the iron barrel/alloy head that Villiers made. Hope this helps.

[subira]

The Cub is spot on, but I quite fancy another project - but can't work out how to explain to the Mrs. how another bike got in the garage.

I noticed a Parkinson Head and Barrel go for what I thought was silly money on ebay last week. As so many Villiers based bikes seem to be fitted with the square set up I was surprised that it went for so much, as I thought that there must be loads about. I take it that they're aren't and that nobody is remanufacturing them like the Serco alloy cylinder for the Cub.

So is the Mick Andrews bike in Trialsworld fitted with the Greeves square barrel then?

[stu]

Yes they are still being made, and if your looking for winning/james beater try one of my Dots, much the same but maybe much better for you.............

[woody]

The Cub is spot on, but I quite fancy another project - but can't work out how to explain to the Mrs. how another bike got in the garage.

I noticed a Parkinson Head and Barrel go for what I thought was silly money on ebay last week. As so many Villiers based bikes seem to be fitted with the square set up I was surprised that it went for so much, as I thought that there must be loads about. I take it that they're aren't and that nobody is remanufacturing them like the Serco alloy cylinder for the Cub.

So is the Mick Andrews bike in Trialsworld fitted with the Greeves square barrel then?

As you mentioned in your first post, there are quite a few alloy head/barrell variants, Parkins, Greeves, Dot, DMW and more that I can't recall right now. Problem with buying one off ebay is it is difficult to know what you are getting, it could be a kart, trials or scrambles barrell and unless you know how to measure the porting and know what the porting should be for each, or know someone that does, you won't know what you've got.

I had what should have been a 250 37a Villers engine in a Sprite with a Parkins barrell and head. Turned out to be a 197 when I took it apart and it wasn't a 37a either I don't think. No-one could identify the barrell, best guess by Vale Onslow was that it was a Greeves and as it was 197, probably a kart barrell. Anyhow, converted it to 250 and when the engine was fired up it had no bottom end at all but revved like hell but it was all wrong for trials, messing with the compression ratio etc did nothing to make it useable. Gave up and sold it. The alloy barrells are a lottery in my opnion, so unless you are sure of what it is I wouldn't buy one - not to mention the stupid money they fetch too, as you've said.

A lot of riders here in the local Pre65 scene reckon that the round iron barrell is a better choice for trials as the porting gives better trials power and some have gone back to those. There's no doubt that the alloy barrells look nicer, it's knowing which one to get that is the problem.

Apparently though, new trials engines can be bought from Nametab in Redditch as I know someone who bought one recently and it had an alloy head/barrell fitted, so maybe someone is casting them again suitable for trials. If you're buying second hand though, beware - there are plenty of 'experts' out there who will tell you what it is but do they really know - in my experience above, no.

Don't know what head/barrell is fitted to Mick's bike.

[charlie prescott]

Hi Guys.

The head and barrel that was on e-Bay last week was a trials barrel from a 1963 CoTTon it was a Parkinson, Developed by the late Ron Parkinson. (Same as on Micks James)

There were not that many of these trials head and barrel's made, Hence I susppect the high price.

Probably bought by someone who is building a Mick Andrews replica James.

Classic Dirt Bike to blame and all the frame builders that are now building replica James frames. So I bet the price of last weeks sale will now be the standard price of any others that come up for sale. So it was probably cheap.

Regards Charlie.

Edited June 26, 2007 by charlie prescott

[trialsrfun]

The last time I saw Mick Andrews bike it was fitted with a Greeves TES type cylinder & head as is Mike Gallaghers James that was featured in the magazine article, having ridden quite a few Villiers/square barrel bikes I have never ceased to be surprised at the performance difference with no two being similar. Much of this could be due to set up and exhaust but whatever you go for have a good ignition.

A heavy flywheel is very important as well the std Villiers trials flywheel weighed in at 7 & 3/4 ibs for the one with the screwed on weight but if you can find one the all brass wheel as fitted to the earlier 32a motors is 8 & 3/4 ibs so whether you run with bob weights or full circle crank you still need a heavy flywheel to prevent it from stalling.

I would not know how much they are changing hands for at the moment but they are about and while not plentiful I think you will find something.

[subira]

Any views on the DMW head and cylinder? I here that these are still available from NVT.

[charlie prescott]

Hi Guys .

Just checked out Norton-Villiers, web site.(Tel01617905277).

They have fullcircle cranks. piston's, electronic ignition, and trials gears, listed but no Alloy head and barrel,

It may be on the DMW site but I can't seem to find it? Is there any more people making square alloy barrels for Villiers engine's . Maybe the 210 kart men perhaps. I would like to know.

PS. Contacted Clive at NV through e-mail, he tells me the head and barrel are available and in stock and can be dispatched to you next day. Hope this helps.

Regards.Charlie.

Edited July 7, 2007 by charlie prescott

[trialsrfun]

The DMW head/barrel is one of the best because it has an extra port above the inlet port at the rear of the liner this helps the incoming charge to push the burnt gases out of the exhaust port, the disadvantage of this barrel is that you need to have the 5 1/2 con rod.

Villiers engines have two con rod lengths 5 1/2 for the 197cc engines and 5 3/4 for the 250cc use the wrong combination and the piston will either stick out the top or stop 1/4 low.

The biggest single difference between a modern two stroke motor and any of the Villiers barrels is the size of the transfer ports and this single factor limits the performance more than anything else as there is simply not enough capacity or space around the crankcases or cylinder to create the port sizes you see on a moderm motor.

I have picures of these barrels etc but I do not know how to add pictures to these pages.

[trialsrfun]

Probably worth mentioning that the real purpose of the aftermarket alloy cylinders was to give increased power which came at higher rpm the bottom end power was / is no better or even as good as the std iron barrel.

While an alloy top half is very desirable why not build the bike with a cheaper iron/alloy cylinder & head and wait until an alloy one appears, simple swap as only the exhaust might need changing.

[subira]

So the final motor with a DMW barrel is a shorter stroke & bigger bore ? Or have I missed something?

[old trials fanatic]

So the final motor with a DMW barrel is a shorter stroke & bigger bore ? Or have I missed something?

As far as i know, of course I.K.B.A. and bar, all the Villiers engines from 9E to 37A are the same stroke and cranks are interchamgeable apart from the invacar ones. There are two con rod lengths as mention previously. The 197cc usually uses the shorter rod so when choosing a barrel make sure the rod matches. You can always put a spacer under the barrel or machine it but it's easier to match the barrel to the rod in the first place.

There are quite a few big bore conversions going the rounds but i dont know of any that are really successful in pre65trials. Pete Carson has one but he has spent ages and ages detuning it as it was an animal when he first got it. He's got it running well now but a lot of work for very little gain I.M.H.O. over a well sorted "std" square Greeves barrel and as said before if it's plonkability you want above top end then the old iron barrel takes a lot of beating. Shame it's so ugly though.

[trialsrfun]

All the Villiers 250s were 66mm bore x 72mm stroke the 1/4 longer rod was to enable a stronger barrel flange to be added (rermember the iron barrel is secured by studs and nuts around the base flange) no capacity difference or anything else it is simply a matter of everything happening a 1/4 further off the floor.

I have owned one of the bigger motors mentioned they were the Moto-X-Motors conversion made by John Burns & Maurice Brayford Maurice uses one to this day, I cannot recall the bore size or exact capacity but it was around 350cc. They do give a much greater power output but are very much heavier than a Greeves or similar top half and still restrricted by the transfer port area. Pete Carson has one as well as someone in the Midland Centre in a Sprite.

The original Greeves square barrels had a chrome on alloy bore finish with no steel liner as well as detachable outer covers over the transfer ports but the chances of ever getting one of these are about the same as winning the Lotto

[charlie prescott]

Hi Guys.

I have just left a P.S. to say that Clive Tomkinson still makes the DMW barrel and head and he says they are in stock he all so can supply the full circle cranks, with both sizes of rod.

As you say the first Greeves barrel's were chrome plated on to the alloy bore, so were the Parkinson barrel's as fitted to the works James? Francis Barnett's of 1964-66.( reg 500 JOH.304,305,306 AKV.etc, and to the Scorpion's of the same year's.

I have found a company that will ceramic coat these alloy barrels, that is said to help engines run smoother , and help carbaration, as there is less blow by past the rings. will post more info when I have been in touch with them.

Regards Charlie.