D.O.H.C. ? I want one of these

dobba99 · Oct 28, 2014

Hello chaps
Following on from the very recent camshaft thread here are the articles about Merlin Engineerings double overhead 8 valve conversion for commandos

Sorry boys but anything else just seems lame by comparison.
regards
Pete

Fullauto · Oct 28, 2014

Ah! The wonders of advertising. I wonder how many they sold?

Bernhard · Oct 28, 2014

found

http://twinshock-chairs.webs.com/apps/p ... d=52384648

http://wasp-motorcycles.tripod.com/

debby · Oct 28, 2014

If you want belt-driven overhead cams, buy a Ducati :!:

kommando · Oct 28, 2014

Les Emery took over development, 'would not touch with a long wooden implement' comes to mind.

lcrken · Oct 28, 2014

kommando said:
Les Emery took over development, 'would not touch with a long wooden implement' comes to mind.

Do you have any more info on Les being involved with the Merlin design? I remember him taking over the Piper 8-valve pushrod head project, doing some more development, and racing a bike with it for a while. But I've never seen any reference to him taking over the Merlin DOHC design.

I believe he later sold the pushrod 8-valve head rights to Andy Molnar.

Ken

Chris · Oct 28, 2014

Hi

Les developed the piper head. We had quite a bit of info in an earlier thread.
The twin cam Merlin is a much rarer beast. Never seen one in the flesh but remember reading about them & being told that the engine was raced hard in a wasp sidecar.

Chris

lcrken · Oct 28, 2014

Pete, thanks for posting the articles. I recall seeing articles about the Merlin conversion back in the day, but didn't save any of them. On one of my business trips to England in the '80s I saw a complete Merlin engine for sale in the classifieds in MCN, and had fantasies of buying it and shipping it back, but couldn't quite make it happen.

The only other info I have is this clip from Roy Bacon's book.

Ken

Rohan · Oct 28, 2014

Someone locally has something similar to that on a late 60s or 70s Triumph 650 twin, done a few years after,
although the drive to the cams was on the timing side.
Apparently it ran very well on the road, he'd ridden it to the show where it was on display.

Can't recall that all-out performance came into the conversation though.
When the dohc can go faster than the motor it sits on top of, bit of a mismatch ?

Thanks for posting article...

comnoz · Oct 28, 2014

The advantage of four valves is not necessarily the added rpm or horsepower capability as it is the ability to have a wider powerband along with the good horsepower. When using two valves you can get good horsepower but it comes with a narrow powerband.
The double overhead cams were likely adopted as an easy way to operate all them valves. Jim

Rohan · Oct 28, 2014

True.

But we can stll dream of a wonderful torquey Commando motor,
that will also turn 12,000 rpms. !

How short stroke would a Commando have to go to be able to turn 12,000 rpm,
we wonder. ??
Without getting out the back of an evelope...

Nater_Potater · Oct 28, 2014

While the DOHC is cool, I'd be more interested in the four-valve-per-cylinder head for the reasons Jim points out. Does anyone make a pushrod variant?

comnoz · Oct 28, 2014

Rohan said:
True.

But we can stll dream of a wonderful torquey Commando motor,
that will also turn 12,000 rpms. !

How short stroke would a Commando have to go to be able to turn 12,000 rpm,
we wonder. ??
Without getting out the back of an evelope...

Oh about 45 to 50mm. Jim

comnoz · Oct 28, 2014

Nater_Potater said:
While the DOHC is cool, I'd be more interested in the four-valve-per-cylinder head for the reasons Jim points out. Does anyone make a pushrod variant?

Not unless you count the one that is on my drawing board. Jim

actually it's a three valve.

Rohan · Oct 28, 2014

Nater_Potater said:
While the DOHC is cool, I'd be more interested in the four-valve-per-cylinder head for the reasons Jim points out. Does anyone make a pushrod variant?

There was mention above, and alsewhere of the Piper 8 valve head - that Andy Molnar acuired eventually. (?).
It wasn't really viable though, and it didn't get into production.

It also made a Commando look like an (ugly) CB250 clone on steroids ....

Rohan · Oct 28, 2014

P.S. Why do these magazine articles never show the working part of an 8 valve - the combustion chamber shape/layout.

For lazy reasons, commercial reasons, or do they sign something that says they won't ?

acotrel · Oct 28, 2014

Rohan said:
True.

But we can stll dream of a wonderful torquey Commando motor,
that will also turn 12,000 rpms. !

How short stroke would a Commando have to go to be able to turn 12,000 rpm,
we wonder. ??
Without getting out the back of an evelope...

Would you personally attempt to ride it ? I would never stroke a big twin down to less than 75mm. It would probably cop 12,000 RPM if the valve gear kept up. You wouldn't have the case and bearings problem in the bottom end. DO IT ! - A 750cc Paton ?

The way to go might be to look at the Nourish Weslake Triumph head and work out how large you can make the bores , then stroke the commando motor to get 750cc, and make barrels and crank to suit. If the Weslake combustion chamber is too narrow, you might end up with a good squish band. There is an 80s Triumph thunderbird which has a steel one-piece 75mm stroke crank.
http://www.motorcyclespecs.co.za/model/ ... 20tr65.htm

Fullauto · Oct 28, 2014

If you REALLY want that, then buy a modern Ducati. All you asked for and more and at a fraction of the cost.

dennisgb · Oct 28, 2014

Fullauto said:
If you REALLY want that, then buy a modern Ducati. All you asked for and more and at a fraction of the cost.

+1

Fullauto · Oct 28, 2014

acotrel said:
Rohan said:

True.

But we can stll dream of a wonderful torquey Commando motor,
that will also turn 12,000 rpms. !

How short stroke would a Commando have to go to be able to turn 12,000 rpm,
we wonder. ??
Without getting out the back of an evelope...

Click to expand...

Would you personally attempt to ride it ? I would never stroke a big twin down to less than 75mm. It would probably cop 12,000 RPM if the valve gear kept up. You wouldn't have the case and bearings problem in the bottom end. DO IT ! - A 750cc Paton ?

The way to go might be to look at the Nourish Weslake Triumph head and work out how large you can make the bores , then stroke the commando motor to get 750cc, and make barrels and crank to suit. If the Weslake combustion chamber is too narrow, you might end up with a good squish band. There is an 80s Triumph thunderbird which has a steel one-piece 75mm stroke crank.

http://www.motorcyclespecs.co.za/model/ ... 20tr65.htm

Oh, and then figure out how many you can sell worldwide..................uhoh.

:shock: