Merlin DOHC Progress (2018)

That’s progress?

I admire your optimism.

Just not as much as I admire your tenacity / obsession !
 
SteveA said:
I have a set o 920 barrels in my workshop that have had every other fin removed. I understand his was done for a sidecar cross outfit where the cooling demands allowed it, and it made it easier to get the mud out!

I bought them quite early in my project.

My Rickman has oil in the frame, which can get very hot and burn my thighs on occasion, so I would not be confident of using these barrels on a road racer.

However, my initial reason for not using them was based on the need to open out the Maney cases I had just bought! (and In the end I built a short stroke 750!)
Click to expand...
Re oil in frame; couldn't some one have made some fins to weld up tp the front downtubes of the bike?
It's easy, sheet metal of a suitable gauge, drill an hole diameter of tube, cut in half and ....viola!
 
Bernhard said:
Re oil in frame; couldn't some one have made some fins to weld up tp the front downtubes of the bike?
It's easy, sheet metal of a suitable gauge, drill an hole diameter of tube, cut in half and ....viola!
Click to expand...
I don’t think that’s necessary as frame tubes act as brilliant heat radiators anyway.
 
Fast Eddie said:
I don’t think that’s necessary as frame tubes act as brilliant heat radiators anyway.
Click to expand...
You clearly haven't touched an oil tank with your bare fingers after a very quick run high speed run or you wouldn't be making this statement!
 
Last edited:
Bernhard said:
You clearly haven't touched an oil tank with your bare fingers after a very quick run high speed run or you wouldn't be making this statement!
Click to expand...
??
I thought we were talking about the relative merits of OIF for oil cooling?

My point was, frame tubes with their large surface area act as very good heat exchangers. Adding fins would undoubtedly increase the heat loss to a degree, but I very much doubt it would be worth the effort involved. It would be far more effective in terms of effort versus gains to fit an oil cooler.

I do know from personal experience gained by converting a race bike to oil in frame, that it can make a tremendous difference to oil, and engine, temperature. Effect on oil temperature was observed via and electric probe thermometer. Effect on engine temperature was observed through running condition after being sat in the warm up area. Both factors were very clear.

I’m really not sure in what way touching a hot oil tank with bare fingers would benefit me in terms of knowledge or experience...
 
FYI I have never owned a bike with an oil cooler, the oif can be kept cooler by fitting fins to the tubes, you see those all over your bike, from the barrel/cylinder head to the Zender heat sink.
My idea would remove oil tank /oil cooler and leave more room for a bigger air box/somewhere to store ta bigger battery for electric starter etc. I'm just saying. . . .
 
Progress update
Took the cylinder head off the Merlin a couple of days ago (after measuring the cam timing, as the cam wheels are only held on tapers, no keys or dowels at all)


It came apart reasonable easily. Evident immediately that Alan and John (who were Merlin Engineering) had used an unmachined (or part machined) barrel casting. The barrels on the Merlin do not have the two outer rear 3/8" BSCY tapped holes, nether the counterbore on the rear through bolt holes or the oil drain hole. Also the front and center tapped holes are 3/8" UNF. The pushrod tunnels are unmachined.
It doesn't have the small holes drilled through between the bores either.


The shaft that take the cam drive across the engine and out the drive side (where the std cam usually lives) has a needle roller bearing in the extended bearing housing



I have identified the cam belt used, its used on a VW Golf, Audi A3 or much to my amusement a Trabant
 
dobba99 said:
Progress update
Took the cylinder head off the Merlin a couple of days ago (after measuring the cam timing, as the cam wheels are only held on tapers, no keys or dowels at all)


It came apart reasonable easily. Evident immediately that Alan and John (who were Merlin Engineering) had used an unmachined (or part machined) barrel casting. The barrels on the Merlin do not have the two outer rear 3/8" BSCY tapped holes, nether the counterbore on the rear through bolt holes or the oil drain hole. Also the front and center tapped holes are 3/8" UNF. The pushrod tunnels are unmachined.
It doesn't have the small holes drilled through between the bores either.


The shaft that take the cam drive across the engine and out the drive side (where the std cam usually lives) has a needle roller bearing in the extended bearing housing



I have identified the cam belt used, its used on a VW Golf, Audi A3 or much to my amusement a Trabant
Click to expand...

Happy New Year dobba99 any new progress updates available ?
 
Evening Wasp wasp
And a happy new year to you!
Hmmm, progress of sorts, If you can call it that.
I bought some of Jim Schmidts long carrillo rods a couple of years ago and from ebay, a second hand piston and barrel from a SV 650 suzuki (81mm bore, same as the 920 pistons )
After i had removed the conrods and pistons from the Merlin I machined up a long dummy crank pin to compare the deck height of the Merlin rod/piston and the carrillo/suzuki piston (this also involved making a dummy gudgeon pin as the suzuki pin hole was bigger than the carrillo little end. By happy coincidence the deck height was the same!


All this enabled me to measure the suzuki piston and order suitable pistons from Jim.
I also ordered a TTI Extra heavy duty 5speed gearbox that is taking a bit of sorting to fit into the Mk3 cradle in the bike that will become Suzi.
Hope to make more progress this year.
Regards and a happy new year to all
 
Wasp Wasp said:
Hi dobba99 Hope you are keeping well,Any new progress updates available on Suzi ?
Click to expand...
Evening Wasp
Progress is/has been slow this last year. I got the TTI box installed in the cradle and had to cut the splines in a Hooke joint for the gearchange shaft (TTI supplied the box with the gearchange shaft parallel instead of at the angle it should be at for the Mk3 installation)
The engine has its own problems that manifested itself upon closer inspection, the cam carriers/cam followers need work as the valve buckets (cam followers) display severe bucket tilt when the cam is revolved. This is because the buckets are not sufficiently supported throughout their travel (and the fact that the clearance when it was made was too wide) The method of valve adjustment is shim under bucket using a lash type cap on top of the valve stem. These caps show severe wear as the buckets had been rocking about when the engine was running, not good.
I am going to make new bucket carriers that will screw/bolt to the underneath of the cam carrier. These will be sized to use triumph triple valve buckets (lighter than the Hillman imp, i think, buckets Merlin used) I am also going to change the valve shim to 13mm dia instead of the lash cap type as they are far cheaper and readiliy available. This entails making different valve spring caps to hold the 13mm shim.
I had the engine in the frame to finalise the g/box assembly, chaincase, headsteady arrangement, petrol tank and timing belt case fitting.
All before the frame was dispatched for painting.
The crankcase has fitted studs bolting the case to the cradle (cradle and case holes reamed together and HT studs made to suit) G/box similar, stepped studs made to suit the cradle/box mounting holes
Primary case has had the oil seal boss machined down and a thinner oil seal fitted to clear the TTi sprocket/nut also the primary rear case has had to have a scallop machined out of the front provide clearance for the cambelt
Headsteady caused a few headaches as it has to use the studs that hold the cam carriers onto the head, longer studs needed/made
This also meant that the petrol tank had to have its underside modified to clear the head and the headsteady
Standard Coil bracket was binned (coils too close to the engine) and a more compact version made to use the std coils in the same area, just further away from the head.
Even the oil feed supply (rocker oil pipe) to the cams took a couple of days to sort out as using braided hose and fittings just didn't look right, so made a compact manifold out of stainless


Along the way in autumn i rebuilt a 1956 ES2 for a club member that had been ripped off by a 'restorer' (a Paint and polish merchant) So bad, it was a death trap, he still won't tell me who did it.
Modified quite a number of harley starters for Mk3s, Sold a few Upgraded/modified prestolite starters. Installed a few master cylinder sleeve kits for owners
Did couple of head gaskets for other owners new to Commandos etc etc.
Got another Mk3 arriving tomorrow for its sprag etc sorting.
Keeps me busy....
 
dobba99 said:
Evening Wasp
Progress is/has been slow this last year. I got the TTI box installed in the cradle and had to cut the splines in a Hooke joint for the gearchange shaft (TTI supplied the box with the gearchange shaft parallel instead of at the angle it should be at for the Mk3 installation)
The engine has its own problems that manifested itself upon closer inspection, the cam carriers/cam followers need work as the valve buckets (cam followers) display severe bucket tilt when the cam is revolved. This is because the buckets are not sufficiently supported throughout their travel (and the fact that the clearance when it was made was too wide) The method of valve adjustment is shim under bucket using a lash type cap on top of the valve stem. These caps show severe wear as the buckets had been rocking about when the engine was running, not good.
I am going to make new bucket carriers that will screw/bolt to the underneath of the cam carrier. These will be sized to use triumph triple valve buckets (lighter than the Hillman imp, i think, buckets Merlin used) I am also going to change the valve shim to 13mm dia instead of the lash cap type as they are far cheaper and readiliy available. This entails making different valve spring caps to hold the 13mm shim.
I had the engine in the frame to finalise the g/box assembly, chaincase, headsteady arrangement, petrol tank and timing belt case fitting.
All before the frame was dispatched for painting.
The crankcase has fitted studs bolting the case to the cradle (cradle and case holes reamed together and HT studs made to suit) G/box similar, stepped studs made to suit the cradle/box mounting holes
Primary case has had the oil seal boss machined down and a thinner oil seal fitted to clear the TTi sprocket/nut also the primary rear case has had to have a scallop machined out of the front provide clearance for the cambelt
Headsteady caused a few headaches as it has to use the studs that hold the cam carriers onto the head, longer studs needed/made
This also meant that the petrol tank had to have its underside modified to clear the head and the headsteady
Standard Coil bracket was binned (coils too close to the engine) and a more compact version made to use the std coils in the same area, just further away from the head.
Even the oil feed supply (rocker oil pipe) to the cams took a couple of days to sort out as using braided hose and fittings just didn't look right, so made a compact manifold out of stainless


Along the way in autumn i rebuilt a 1956 ES2 for a club member that had been ripped off by a 'restorer' (a Paint and polish merchant) So bad, it was a death trap, he still won't tell me who did it.
Modified quite a number of harley starters for Mk3s, Sold a few Upgraded/modified prestolite starters. Installed a few master cylinder sleeve kits for owners
Did couple of head gaskets for other owners new to Commandos etc etc.
Got another Mk3 arriving tomorrow for its sprag etc sorting.
Keeps me busy....
Click to expand...

that’s a remarkable service to other owners!
 
Hi,
I‘m in awe of your work and commitment to Nortons.
The question I have to ask is what is the point? No, I’m not being rude, it is a serious questions and I am really impressed but I was under the impression that OHC and DOHC in particular was to allow higher rpm than is possible with a pushrod engine which is limited by the inertia of the valve train. As has been discussed in great detail in a recent thread, the maximum rpm a Commando can endure is limited by its basic engine design, particularly it‘s bottom end. What rpm are you hoping to run the engine at?
Interestingly one of the most impressive bikes (for what it is) that I have ridden was my late mate‘s T140V (small tank) with a Norish 8 valve head (not sure if there were other engine modifications). It absolutely flew and as I have a similar T140V (breadbox) I could be quite sure of the performance increase. Of course it managed this with standard pushrod design.
So, has anybody tried an 8 valve head? I’m told that engine geometry has a lot to do with what gains in power are available.
Can you direct me to any articles etc on the Merlin engine?
Anyway, good luck with the project and keep posting.
regards
Alan
 
I have not even lightened and polished the valve gear on my 850 motor, because it cannot be safely taken above 7000 RPM due to the bottom end. The valve gear is not the limiting factor, DOHC might allow the use of a more radical cam, however that would probably change the power delivery charactristics and make the bike more difficult to ride. So I would end up going slower.
 
Alan L said:
Hi,
I‘m in awe of your work and commitment to Nortons.
The question I have to ask is what is the point? No, I’m not being rude, it is a serious questions and I am really impressed but I was under the impression that OHC and DOHC in particular was to allow higher rpm than is possible with a pushrod engine which is limited by the inertia of the valve train. As has been discussed in great detail in a recent thread, the maximum rpm a Commando can endure is limited by its basic engine design, particularly it‘s bottom end. What rpm are you hoping to run the engine at?
Interestingly one of the most impressive bikes (for what it is) that I have ridden was my late mate‘s T140V (small tank) with a Norish 8 valve head (not sure if there were other engine modifications). It absolutely flew and as I have a similar T140V (breadbox) I could be quite sure of the performance increase. Of course it managed this with standard pushrod design.
So, has anybody tried an 8 valve head? I’m told that engine geometry has a lot to do with what gains in power are available.
Can you direct me to any articles etc on the Merlin engine?
Anyway, good luck with the project and keep posting.
regards
Alan
Click to expand...
'Classic Bike' magazine, June 1988, has an article on 8 valve Commando.
 
Alan L said:
So, has anybody tried an 8 valve head?
Click to expand...
Norton comissioned Piper engineering to design and make an 8 valve head to fit the standard barrel. When tested it didnt perform any better than the 4 valve std head so wasnt adopted. Les emery got hold of it and had Pete Lovell go over it. He found the valve springs were far too strong and other stuff. When he got it going, fitted with the softest cam ever, he found it a very tractable and torquie motor that was deceptively fast. It was road tested by one of the bike mags of the day.
Pete Lovell told me that they, presumably LE, then put a race cam in it and promptly ruined it as it was never as good the soft cam engine
If you look at a std 850 barrel it has already got the metal at the rear to accept the 8 valve bolt hole pattern
 
My understanding is that Andy is continuing the development of the Piper head. But, it has turned into a bigger job than initially expected to get it how he wants it.

Andy has some good experience with 4 valves per cylinder, his 4 valve Manxes go very well and are very reliable, despite fairly limited development (compared to the 90+ years of continual development the 2 valve engine has had).
 

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