Merlin DOHC 8 valve Cylinder head drawings

The 35 year old dream to build the ultimate commando just got a whole lot nearer.
I have just acquired the drawings and basic patterns for the Merlin DOHC 8 valve cylinder head...
Just hope i can do them justice before i,m too old to enjoy thrashing it....

Cool! I remember seeing an article about the conversion in one of the bike magazines a long time back. As I recall it was a 920. Hope you can manage to sort it all out in time.

Ken

Are those linen drafting cloth?

Well, Peter, all I can say is "good luck". This is no easy task, especially for a one off. Believe me, I know what it takes and unless you have somebody who knows what they are doing and can make up the tooling etc, and then find a foundry to cast it, successfully, you are looking at a very expensive, time and money consuming enterprise that may leave you with something unusable. Cams will have to be ground to suit the four valve layout, as the requirements are different for two and four valve applications. Pistons are also another consideration.

If you have access to this stuff, try to find out why they didn't succeed and therein will be your answer. But, if it's your dream, go for it and good luck !

Wow. Good luck Dobba and total respect to you for having the balls to give this a go.

Despite the nay sayers, there is no reason at all why this shouldn’t result in an awesome motor. Especially if you design it around a 920 platform.

The BIG difference between this and NRE however is that there is no racing market for 8 valve Norton’s (as far as I’m aware). So, IF you’re planning on selling these, it’ll only be extreme nut-job hot-rodder types.

Pistons are easy to get made these days.

Yes, some work in optimum can design would be advisable, I’d say snotzo might be of assistance here. But when you look at NRE and Triumph, the cam profiles are very interchangable twixt the two.

I’d be interested...

Very interesting, Dobba99. Rather than the possibility to build another DOHC head, I'd be interested to know the story behind the plans and the patterns. Did they reside with Merlin Engineering to this day, or with Pete Lovell, whom I believe was involved in the project? I note the date of drawings is 1979. It is really surprising that drawings are of such low quality. By 1979 CAD had replaced drafting boards in engineering, at least for complex tasks, and this project definately is one. Even so, at least I would have expected quality drawings made on a drafting board, but these drawings seem to be made to even lower standards. Maybe you didn't obtain the final drawings from the project? In any case, I would be most interested to learn more about them, if you are able to dig up the story.

If you decide to realize a new prototype, I suggest you invest in a proper 3D design model which allows you to play around with key parameters.

-Knut

Fast Eddie said:

Wow. Good luck Dobba and total respect to you for having the balls to give this a go.

Despite the nay sayers, there is no reason at all why this shouldn’t result in an awesome motor. Especially if you design it around a 920 platform.

The BIG difference between this and NRE however is that there is no racing market for 8 valve Norton’s (as far as I’m aware). So, IF you’re planning on selling these, it’ll only be extreme nut-job hot-rodder types.

Pistons are easy to get made these days.

Yes, some work in optimum can design would be advisable, I’d say snotzo might be of assistance here. But when you look at NRE and Triumph, the cam profiles are very interchangable twixt the two.

I’d be interested...

Click to expand...

Naysayers? Where? Imagined?

Many thanks for the encouragement, i know this will be quite an involved project but i think i can do it.
how i came by the drawings is quite simple, i rang Merlin (they are still in business, at least for a few more months...) and asked them if they still made them. 'We havn't done one of those for years' came the answer and 'we are retiring later this year' so they making me one was a no go. After i had talked to them for a few more minutes about it I inquired if they knew the whereabouts of the three heads they made. They think L.Emery has one and one went to wales and the last one might be in the south west of the country. last resort, i asked if they still had drawings. 'Mnnn, we might have. Give us a ring in the new year'
So i did last week. 'give us a ring in a week. We'll have a look'
Thursday this week i phoned them again. 'Yes we have found the originals' I couldn't believe my luck. I had all but written off them finding anything. I said i will be there the following morning (yesterday)
I must say i found John and Alan two of the most helpful and amenable chaps i have ever met They were up to their ears in JAP engine castings and flywheel assemblies (what has been their bread and butter work for years).
Yes they are in poor condition (all drawn on draughtman's tracing paper) but the information is all there. They even still had the drawing board that they were drawn on. propped up against the roller shutter door!
My intention is to first draw them up in Autocad whilst following up the contacts and information John and Alan gave me regarding where and what suppliers i will need (Foundry they use is quite local to me)
They made it to use in sidecar cross and it led to them making the Wasp engine for Robin Rind Tutt. They even showed me the drawings for a two stroke engine they made for sidecar cross use... Now that was awesome they said.

mdt-son said:

...By 1979 CAD had replaced drafting boards in engineering....-Knut

Click to expand...

Not that early in the machine tool industry in New England where I worked, but I strongly agree that now getting it redrawn as a 3D model is an excellent suggestion.

Fullauto said:

Naysayers? Where? Imagined?

Click to expand...

I’m not accusing anyone on this thread Ken, in the past however, their have been many who said the prototype wasn’t up to much.

And perhaps they were right, but all I’m saying is that based on how good a Nourish motor is, there’s no reason an 8 valve Commando couldn’t be a cracker!

The 8 valve head has been tried and tested on a pretty much stock motor, ever wondered why it is not made, yes, it worked but was off no real benefit. It needs a whole new dynamic to work, stroked crank, different height barrel, pistons are taken to the limit with an 8 valve head. Work all this out and it will give much benefit, but just how much Norton motor is left. Ring those that have machined, built and tested them on a Commando and you will save yourself a whole lot of dosh. I'm sure Emery would not have passed up the chance to sell it otherwise, he flogs parts dubious, not dead horses.

From what I can remember the cam area was the easy bit, and this was an area of benefit. Piston and crank in the current size are limiting factors. Ahead of its time Norton wise, but the rest of the motor has not changed enough for it to achieve full potential.

Without a whole host of modification it will still only work in the existing operating envelope that a big valve head can mange, different yes, but no enhancement. Some will also spot the issue in the first photo above.

As for cad in the UK, most machine shops use cad machines, but a few top end machine shops use it fully connected and integrated with a CMM suite and remotely operated interchangeable tool racks on the latest machines, some places are now gearing up to have a 24hr capability without a human on the floor, but most machine shops are still 25 years behind. In the late 70's and early 80's I doubt few had the latest capability to machine an 8 valve head efficiently.

Being negative, no, the head worked, sort out the expensive limiting factors and it will open up a whole new level of power - just how deep are your pockets!!

I bought and have been reading with interest the new book Norton-The Bible

In the book it is briefly mentioned that Norton did experiment with a four valve DOHC head but abandoned the project due to the power output being disappointing compared to the stock layout, of course this was before even the Commando beginnings, I think in the 50s

Might search up what Harley and its after market suppliers did to make 4 valve heads, which caused other changes to tolerate extra heat produced both for protecting the "tain't" area bewix exht valves and detonation on ign timing for best power. This involved stroke changes, gasket changes and internal fluid cooling paths. After market heads w/o these features are no longer available as word spreads fast in Harley crowd. Might consider staggered valve opening for swirl effect in rpms Nortons and Harleys can tolerate.

Interesting comments. Please explain 'pistons are taken to the limit with an eight valve'
'Ring those that have machined, built and tested them on a commando and you will save yourself a whole lot of dosh'
That is precisely what I have done. Obtained a proven design from the two people who have done so.
Also what was the issue in the first photo? I'm intrigued to find out.

I think the reason why only three were made was the cost, 1200 pounds back in 1980 and that was you suppling the base engine.
Given that a brand new bike was around that price then in relative terms the cost could be around 15000 in today's money.
Makes the full auto head very good value. You do get a lot of work for the money and an improved item over the original
Here are the articles I saved from Motor cycle weekly way back in 1980

Madnorton said:

The 8 valve head has been tried and tested on a pretty much stock motor, ever wondered why it is not made, yes, it worked but was off no real benefit. It needs a whole new dynamic to work, stroked crank, different height barrel, pistons are taken to the limit with an 8 valve head. Work all this out and it will give much benefit, but just how much Norton motor is left. Ring those that have machined, built and tested them on a Commando and you will save yourself a whole lot of dosh. I'm sure Emery would not have passed up the chance to sell it otherwise, he flogs parts dubious, not dead horses.

From what I can remember the cam area was the easy bit, and this was an area of benefit. Piston and crank in the current size are limiting factors. Ahead of its time Norton wise, but the rest of the motor has not changed enough for it to achieve full potential.

Without a whole host of modification it will still only work in the existing operating envelope that a big valve head can mange, different yes, but no enhancement. Some will also spot the issue in the first photo above.

As for cad in the UK, most machine shops use cad machines, but a few top end machine shops use it fully connected and integrated with a CMM suite and remotely operated interchangeable tool racks on the latest machines, some places are now gearing up to have a 24hr capability without a human on the floor, but most machine shops are still 25 years behind. In the late 70's and early 80's I doubt few had the latest capability to machine an 8 valve head efficiently.

Being negative, no, the head worked, sort out the expensive limiting factors and it will open up a whole new level of power - just how deep are your pockets!!

Click to expand...

Yep sir - can't wait to read how other engine changes are figured out and then done. Awesome don't have to be practical but good goal to seek. Imagine mirror imaging another head to fit/function on a Norton V4.

Ponder - Harley nixed hemi head, made chamber/piston flat, added a center and side sparkplug to get ign adv down to 25' to lessen surface heating area and time area is exposed to combusting heating before turning into mechanical action. Pro/con blogs imply four better than two valves even lower revs but took 4000+ to feel most difference. Some comparison examples said often the 2 v twin made same power at 6000's while the 4v had to hit 7000's to match.

Thanks for posting the article , dobba99, particularly in .pdf format. The article has been posted on this forum before, in .jpg format, which I also downloaded at the time, but I have forgotten who posted it. Always interesting to see the details of the more interesting experiments. I had a look at the Piper heads at Mick Hemmings shop many years ago, and lusted after them. Mick said he was saving them for his retirement funding. I guess that time has arrived.

Ken

Its not just a question of 4 valves vs 2 (although 4 is, of course, better). The other point is that you would have a complete bank canvass upon which to design ports and decide port sizes and maximise benefit from squish, reduce advance due to better combustion, etc, etc.

I really pushed the development of 2 valve Triumphs when racing them and peaked at 75rwhp. My NRE modded Triumph racer was 84rwhp and I never really tried to develop it much.

I think the real bottleneck will be the rest of the machine. When the power goes up, the stock crank, rods, cases, gearbox all take turns at become the weakest link !

Not to mention the stock forks, shocks, brakes, etc...

But I’m sure Dobba has already worked this out!

A tuned Norton twin could make 100 bhp if it could rev to 10 grand or more. But it can't, so spending capital on more valves or OHC isn't gonna yield much heretofore unattained horsepower. Make the botton live and you can start to extract more juice from the top.

An eight valve head would allow the engine to spin faster, but the at the time they would have had been constrained with numerous issues. You have piston speed and life to contend with, standard pistons are at limit, yes they will go faster but life will decrease and failure potential will increase. So to get around this you then need to stroke the engine to achieve a piston speed that will work for you, now you'll need to bore to suit. Now you have a valve springs working, piston speed controlled then you need to get the crank to spin, as other have pointed you need faster crank speed. At 7000rpm or thereabouts, it is reckoned by some that with a standard crank you have about 22 ton trying to escape your cases, to get to higher revs the increase is not linear, MK3 cases may not be upto it.

Even today the Merlin head could no doubt be improved upon, with the rest of the power unit modified to suit, it would be one hell of an engine, but personally feel it would not constitute a Norton engine, just a drop in replacement high performance engine for a Commando.