I could just scream!

marshg246

marshg246

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Some time back bought a partly built Combat. It was being put together with a monster single carb, a Harley oil tank, extended forks and supposedly a professionally rebuilt engine. I have a customer who wants a stock Combat. So, I started on it. If interested, the writeup of the build is here: https://www.gregmarsh.com/MC/Norton/CustomerCombatBuild.aspx

The engine cases were not cleaned up when it was built so apart it came - found plenty of problems so it was good that I took it apart.

Everything was going OK but on the first quick test ride, I noticed a little oil smoke from the left exhaust. It didn't clear up so I figured that the valve seal had split or come off. The bike ran very strong and was more of a bear to kick than the last Combat I built but I figured that was the new +.020 over pistons, new valves, new cam and so on. So, using the rope trick, I removed the springs from the left-side intake. The seal was fine. So, something I truly hate and have trouble doing by myself on a Norton had to happen - off with the head.

If quickly became apparent that the new copper head gasket was bad. I should have inspected it before installing but I didn't. I didn't have another in stock so I reassembled with fire-ring composite gasket. Started the bike and there was a noise that wasn't there before - WTF! So, off with the head again. My stepson was helping me and thought he heard something fall out of the head. So, another new head gasket and back on. Now the noise was louder!

Today, I took the head off again and can see where the left exhaust valve is just touching the piston! I compared the head to another Combat head and it has clearly been decked! I should have caught it before when I noticed that the rocker adjusters barely stick out of the rockers! I haven't done any precision measuring but it looks like .020-.030 has been taken off the head. It is flush with the bottom fin.

It's a real shame since the head has new guides, black diamond valves, and new springs. I hope the spare head I have is has good guides and seats - it has no valves.
 
marshg246 said:
Some time back bought a partly built Combat. It was being put together with a monster single carb, a Harley oil tank, extended forks and supposedly a professionally rebuilt engine. I have a customer who wants a stock Combat. So, I started on it. If interested, the writeup of the build is here: https://www.gregmarsh.com/MC/Norton/CustomerCombatBuild.aspx

The engine cases were not cleaned up when it was built so apart it came - found plenty of problems so it was good that I took it apart.

Everything was going OK but on the first quick test ride, I noticed a little oil smoke from the left exhaust. It didn't clear up so I figured that the valve seal had split or come off. The bike ran very strong and was more of a bear to kick than the last Combat I built but I figured that was the new +.020 over pistons, new valves, new cam and so on. So, using the rope trick, I removed the springs from the left-side intake. The seal was fine. So, something I truly hate and have trouble doing by myself on a Norton had to happen - off with the head.

If quickly became apparent that the new copper head gasket was bad. I should have inspected it before installing but I didn't. I didn't have another in stock so I reassembled with fire-ring composite gasket. Started the bike and there was a noise that wasn't there before - WTF! So, off with the head again. My stepson was helping me and thought he heard something fall out of the head. So, another new head gasket and back on. Now the noise was louder!

Today, I took the head off again and can see where the left exhaust valve is just touching the piston! I compared the head to another Combat head and it has clearly been decked! I should have caught it before when I noticed that the rocker adjusters barely stick out of the rockers! I haven't done any precision measuring but it looks like .020-.030 has been taken off the head. It is flush with the bottom fin.

It's a real shame since the head has new guides, black diamond valves, and new springs. I hope the spare head I have is has good guides and seats - it has no valves.
Click to expand...
I detuned my mates combat for him by fitting a 1mm decompression plate under the barrel
You could do the same and use your existing head
 
Last edited:
I have just had the head off my Trident three times. It is all sorted now and I have already forgotten
the drama. It is always best to examine and know rather than think you know.
Let us know how it goes.
 
Onder said:
I have just had the head off my Trident three times. It is all sorted now and I have already forgotten
the drama. It is always best to examine and know rather than think you know.
Let us know how it goes.
Click to expand...
I thought I heard some blood curdling high pitched screams from the South West… at first I thought it must be the Beast of Bodmin.. but now I know…
 
Screaming is for the first time. By the second time it is quiet resignation. The third time is the re-enactment of the Bataan Death March. And no, that isn't a John Phillip Sousa number.
...but it is all just a walk in the park if you get results. Bike runs well, major improvement over the standard 750 cc. If it holds together I must say the seduction of a stroked crank shimmers!
We all need more torque.
 
You need to use Personal Psychology with these problems: "Oh no, the oil pressure is a tad weak. I BETTER GET THE CRANK GROUND AND THOSE RODS ARE NEARLY 50 YEARS OLD..."
And that is how you justify the expense of the stroker crank and new rods. It is only a little bit more than grinding the crank and getting new rods.
I am a genius.
 
Onder said:
You need to use Personal Psychology with these problems: "Oh no, the oil pressure is a tad weak. I BETTER GET THE CRANK GROUND AND THOSE RODS ARE NEARLY 50 YEARS OLD..."
And that is how you justify the expense of the stroker crank and new rods. It is only a little bit more than grinding the crank and getting new rods.
I am a genius.
Click to expand...
You have progressed well Grasshopper…
 
A longer stroke delivers more torque.

That means more drive with less rpm.

That means less throttle opening.

That means less fuel consumption.

So, basically, you’d be doing it for environmental reasons.

In fact, NOT doing it makes you a climate change denier…
 
It gets worse! I just carefully measured as best I can with calipers. The timing side was decked .023" and the drive side .028"! Clears up why only the drive side exhaust valve hits. Hard to believe a machinist would be off .005". I checked the other head I have, and it is less than .001 difference side to side.
 
marshg246 said:
It gets worse! I just carefully measured as best I can with calipers. The timing side was decked .023" and the drive side .028"! Clears up why only the drive side exhaust valve hits. Hard to believe a machinist would be off .005". I checked the other head I have, and it is less than .001 difference side to side.
Click to expand...
Just ask Jim for a tapered gasket …
 
While going through my spare heads, I came across this one. At first, I thought it was a 750 Combat but they have the "C" stamped into them, not raised. Then I measured and it's an 850 head with a little less than 30mm intake ports. There is no "RH" number. What is it? There's one for sale on eBay right now too: https://www.ebay.com/itm/234530154817?hash=item369b162941:g:s9gAAOSw-S1iarMw



I could just scream!
 
marshg246 said:
While going through my spare heads, I came across this one. At first, I thought it was a 750 Combat but they have the "C" stamped into them, not raised. Then I measured and it's an 850 head with a little less than 30mm intake ports. There is no "RH" number. What is it? There's one for sale on eBay right now too: https://www.ebay.com/itm/234530154817?hash=item369b162941:g:s9gAAOSw-S1iarMw



View attachment 94967
Click to expand...
Looks like a pre cdo head , the devil bay one more like an Atlas early 23166...................
 
Ref the eBay head, dumb question from someone with zero pre Commando knowledge: how do the rockers get fed with oil ?
 
I guess I'm not living right! The spare Combat Head I was planning to use has a bad seat. No problem - I have a half-built bike with an engine "built by a famous builder". So, Off with it's head. Impressive - new everything including guides and seats, and it has brass exhaust inserts and steel pushrods. It has been installed with a fire-ring gasket a copious amounts of sticky sealer so I had a lot of cleaning to so. It went on easily. I was following the normal tightening sequence but I do it in three stages. About 10ft-lb, then about 20ft-lb, and finally to spec. The drive side front stud pulled from the head well before 10 ft-lb :mad: Of course I have every thread repair kit you would want for a Triumph or Commando, except 3/8 x 20 BSF!
 
I'd probably slap that head on there and use fatter JSM copper base and head gaskets. If there is barely any adjuster on top at the rocker, the push rods are on the short side. They will be really short with a thicker base gasket and copper head gasket. If the other way around very little adjuster on the valve tip, the push rods are on the long side. Time before my last build the composite gasket ended up at .031 when compressed. Gotta think a little about that.

If I was building Norton engines for a living, I'd probably be spending any profit I made on booze, but I digress. I would always talk the customer into the stud inserts. Early Norton heads are made of silver painted cheese.

I know you already know all that. I'm just babbling today cuz it's raining.
 
Schwany said:
I'd probably slap that head on there and use fatter JSM copper base and head gaskets. If there is barely any adjuster on top at the rocker, the push rods are on the short side. They will be really short with a thicker base gasket and copper head gasket. If the other way around very little adjuster on the valve tip, the push rods are on the long side. Time before my last build the composite gasket ended up at .031 when compressed. Gotta think a little about that.

If I was building Norton engines for a living, I'd probably be spending any profit I made on booze, but I digress. I would always talk the customer into the stud inserts. Early Norton heads are made of silver painted cheese.

I know you already know all that. I'm just babbling today cuz it's raining.
Click to expand...
Since the head was decked crooked, a thicker head gasket is not the answer unless I had a machine shop correct that in which case I would need a 2mm head gasket.

Installing thread inserts is easy and I have almost all sizes. The hard part on these is getting them absolutely perpendicular to the head. This is the first one I've ever had pull so I had to order the kit to fix it and they are out of stock everywhere I checked until the last place who had one in stock. It's a brand I'm not familiar with but since the company is AU based I'm hoping it is quality.
 

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