Mitch's 72 Engine Rebuild

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htown16

htown16

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This is a new thread I am starting for the rebuild of the engine for my 72 basket case.
Here are a couple of shots pre-teardown.
Mitch's 72 Engine Rebuild

Mitch's 72 Engine Rebuild

Vin number is 211223 with Aug 72 stamped on the plate. Must be one of the last 72's built. No evidence of a "C" on the head, but has 32 mm carbs.
Mitch's 72 Engine Rebuild

Exhaust ports have been repaired.
Mitch's 72 Engine Rebuild

valves and piston tops have been cleaned and a new head gasket present. But apparently engine was never started again.
Mitch's 72 Engine Rebuild

I'm wondering if this was at same time exhaust port repair was made.
I'm a little concerned about the amount of heat used to repair the exhaust ports. Could it have possibly warped head. I have a really nice 73 rh6 head I could use in place of this one.
 
Have you removed the studs and checked how flat the head is with a straightedge ?

Cylinderheads get pretty hot in normal use, if they curled up like a pretzel any time they got hot we'd all be walking. And aluminium in large lumps tends to melt before it warps...

Hopethishelps.
 
"Vin number is 211223 with Aug 72 stamped on the plate. Must be one of the last 72's built. No evidence of a "C" on the head, but has 32 mm carbs."

Roy Bacon in Norton Twins Restoration says 211110 was the first detuned '72 combat, not sure what that meant. Using the RH6 head is a good option, but really depends on what state of tune you want to end up. For my combat, I've taken the attitude if I want lower performace, rather than detune it, might as well buy another machine.
 
looking at this photo it does NOT appear to be a combat head. the combat will show almost smooth to the first fin and the 2 bumps in front of the exh valves will also be machined smooth.a word of caution DO NOT do the sump mod as GRANDPAUL and OLD BRITTS show as it is IMHO the the wrong way to do this. I also would NOT recommend to do the 850 style breather mod but instead use jim comstock's read setup in the original position. feel free to PM me with any questions as to how to do this.

htown16 said:
This is a new thread I am starting for the rebuild of the engine for my 72 basket case.
Here are a couple of shots pre-teardown.

Vin number is 211223 with Aug 72 stamped on the plate. Must be one of the last 72's built. No evidence of a "C" on the head, but has 32 mm carbs.

Mitch's 72 Engine Rebuild

I'm wondering if this was at same time exhaust port repair was made.
I'm a little concerned about the amount of heat used to repair the exhaust ports. Could it have possibly warped head. I have a really nice 73 rh6 head I could use in place of this one.
Click to expand...
 
This is not a Combat milled head but a reversion to standard compression as the disasters piled up under warranty. The camera has warped the image of studs or Lysergic acid dilythomide was applied earlier.
 
Yea , pull the studs , lap flat on glass . THEN youll know if its warrped like a bananna :lol: :P

WHILE YOURE DOING IT , cut a strip of cardboard 32 mm wide . If it goes down the port , Plane
the head and throw in a SS Cam . Its a lot of old woman going on , about Combats .

What wouldve happened to 250GTO Ferraris if 18 yr olds couldve got em on $ 200 deposit . :?: :wink:

Head could be the tapered 32 to 30 as ya go in , or could be 32 to 30 manifolds .

A good keen man would open the ports to 32.5 and fit the 1 5/8 valves . :D
 
Here's Peel's early unmolested Combat head that show the slight machining of the casting flats and ID stamping. I'd stick to the small port head and up the CR by not using a gasket just Hylomar and enjoy 2S cam coming on stronger and earlier than big port slug flow head, unless you plan to wait till 6900 to feel the 2S kick in.

Mitch's 72 Engine Rebuild
 
What a nice head, Hobot. (Oh boy !!)
Why isn't it on a bike out carving up the twisties ?

BTW, anyone know who "Birco" are ?
Imagine that Birmingham is going to come into this somewhere
 
BTW, it is recommended that before fitting such heads, that each hole be lightly countersunk around first. Removing the studs first, of course.

This prevents any little mountains of metal pulled up around the stud from interfering with the head pulling down quite flat onto the cylinder.
 
"a word of caution DO NOT do the sump mod as GRANDPAUL and OLD BRITTS show as it is IMHO the the wrong way to do this. I also would NOT recommend to do the 850 style breather mod but instead use jim comstock's read setup in the original position"

Having done these mods in 1998 when rebuilding my combat, I would agree with above and would not do it again.
 
That is the rear stud and it was only screwed in finger tite and its nut was loose. Apparently there was some work done on this engine and then the project was abandoned. Given the condition on the outside of the engine that was a long time ago.
All the studs show a little pull up of the threads. What should I use to chamfer them?
I was not planning on doing the crank-case mods. From what I've been able to gather from info from the time is that the problem was with scavenging during sustained high rpm operation. Given this is to be a street bike, I think I will leave it as is. The reed valve looks like a slick piece. Have to see if there is any money left in the budget.
 
htown16 said:
That is the rear stud and it was only screwed in finger tite and its nut was loose. Apparently there was some work done on this engine and then the project was abandoned. Given the condition on the outside of the engine that was a long time ago.
All the studs show a little pull up of the threads. What should I use to chamfer them?
I was not planning on doing the crank-case mods. From what I've been able to gather from info from the time is that the problem was with scavenging during sustained high rpm operation. Given this is to be a street bike, I think I will leave it as is. The reed valve looks like a slick piece. Have to see if there is any money left in the budget.
Click to expand...

With the XS650 reed valve so cheap there's no excuse not to do something.
 
Yeah, like spend the $17,a true reed valve . XS650 ! ...and order in the $75 brake M.C. with lever while yer at it. Move all switches to the left.
 
Well the tear down continues and so do the suprises.
Bores look pretty good except for a little corrosion where the rings were sitting.
Mitch's 72 Engine Rebuild

Pistons and rings are +.020 and look almost new, but unfortunately are the early type with the thermal slots. Not correct for a 72 I don't believe.
Mitch's 72 Engine Rebuild

Better shot of the bores, some cross hatching showing.
Mitch's 72 Engine Rebuild

Limited view of cam and rods looks like they are okay.
Mitch's 72 Engine Rebuild

Lifters look okay to me. Any thoughts?
Mitch's 72 Engine Rebuild

Was thinking about sticking the barrel in a bucket of Evaporust. Any reason that might not be a good idea?
 
I'm not there to inspect but things look acceptable. My 72 uses those pistons and I wail about on them all day, standard bore original ,very little oil consumption,carefull assembly of ring positions helped.Cam and lifters look acceptable but there are others who would disagree I'm sure. Just for fun using a flashlight look for the bronze cam retaining washers with bent over tabs into timing case hole for locating purposes. These have microcracks at tab bendover points that can fail or not. Going to split the cases to clean out the sludgetrap I assume ?
 
Aye Slooted pistons reputed to drop skirts if 6000 exceeded regularly , or at all ?

The tang on the thrust washer was the correct size to go through oil passage and stall Oil Pump gears . :oops:

Therefore nipping of at the bud ( or circumferance ) was considered rational . Later ones have no tag / tang ???
 
If the slots are not all the way across running under the oil control ring it should be ok. Is it going to be a street bike?
CNN
 
Yeah, street bike. Will check the size of the slots when I get the pistons off. Planning on going ahead and splitting the cases while the motor is out.
 
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