Head gasket question for Jim Schmidt or others

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BrianK

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Off with my head! Soon anyway, for some needed attention. 1973 850.

I have a composite gasket in there now, from my last trip in (rings). Been fine. But thinking of going copper this time, and have my cart stocked at Jim's.

I believe the 0.42 thickness is standard, yes? And assuming so, is there a gain to be had (without danger to valve gear, and no I'm not going to clay it; too lazy (no comment please)) from going to 0.32?

Tx - B
 
BrianK said:
Off with my head! Soon anyway, for some needed attention. 1973 850.

I have a composite gasket in there now, from my last trip in (rings). Been fine. But thinking of going copper this time, and have my cart stocked at Jim's.

I believe the 0.42 thickness is standard, yes? And assuming so, is there a gain to be had (without danger to valve gear, and no I'm not going to clay it; too lazy (no comment please)) from going to 0.32?

Tx - B
Click to expand...
Don't know the answer but I think you meant 0.042" and 0.032" since 0.42 is 4/10" and the thickest he can get is 1/8" (0.125")
 
You be safe a thinner gasket might give a bit more compression but not really it's so minuet, everyone has their favorite head gasket but I have always used copper head gaskets.
 
Jim can answer one other confusion for me. He lists for both 750 and 850 0.042" and 0.062" as standard. Only guessing because I haven't measured, but I think the AN copper head gaskets are 0.062 (1/16")
 
Standard copper is around .040" and composites are closer to .035" .032" should be no problem unless your head has been milled.
1/16" is for lowering compression or for a head that's been milled too far.
 
Here's a bunch of completely obvious unsolicited babble:

Both the barrel deck and mating surface on the head need to be as flat as possible with a copper head gasket. Also helps if the 3 studs in the head have thread inserts, cuz if they start to go on a retorque you will probably have a head gasket leak. Permatex Copper Make a Gasket spray is much easier to apply to both sides of the copper head gasket than anything else out there, and it holds and seals the head gasket on a street bike. Read the instructions on the can. Don't be in a big hurry to install the head gasket once it is sprayed. Let it get tacky, but no longer slippery.

You can of course join the I never use sealer on copper head gaskets crowd, but it's a crap shoot if the deck or barrel surfaces are not perfect.

I run a 750 engine with no base gasket and Jim's .032" copper gasket and his high compression pistons. The head was minimally re-surfaced for flatness last century. The difference between a .040 and .032 head gasket without a base gasket is noticeable at the kick start. I can't kick through the compression stroke when the engine is stone cold unless the spark plugs are out. I'm an old guy though, so there is that. I also think my SS cam has something to do with it, but I digress. If your pistons have valve cutaways there won't be a problem with piston to valve clearance especially with a stock cam.
 
If you are concerned about the clearance between valves and pistons, normal practice is to fit the head with pieces of plasticine on the crown of the piston, turn the motor over - the remove the plasticine and section it with a razor blade. Most people probably do not use high-lift cams in Commando engines. Machining heads and barrels to get higher compression is stupidity. Compression ratio, ignition advance and jetting form a balance. The same effect which is achieved by raising compression ratio can be achieved by increasing ignition advance or leaning-off the jetting. If you get more go by raising compression, you were previously probably jetted too rich. Better carburation might be a better way of gaining performance than machining heads and barrels. In the 1970s, every model change of Japanese motorcycles from the same manufacturer had very different jetting in the carburetors, when compared with the previous model.
 
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I just measured three 750 and three 850 new form the package Andover Norton copper head gaskets. All were between .0445" and .0455". I also measured one 750 and two 850 Composite gaskets new from the package Andover Norton composite head gaskets. All were marked 1.00 which I assume is 1mm (.0394"). I measured the composite, not the fire ring. All were .0393" to .0402".

I still don't know why Jim lists .042" and .062" as standard for both 750s and 850s.

Yes, all measurement were taken using a verified micrometer, not caliper.
 
marshg246 said:
I just measured three 750 and three 850 new form the package Andover Norton copper head gaskets. All were between .0445" and .0455". I also measured one 750 and two 850 Composite gaskets new from the package Andover Norton composite head gaskets. All were marked 1.00 which I assume is 1mm (.0394"). I measured the composite, not the fire ring. All were .0393" to .0402".

I still don't know why Jim lists .042" and .062" as standard for both 750s and 850s.

Yes, all measurement were taken using a verified micrometer, not caliper.
Click to expand...
.042" is only .002" away from ,040". Show me where on my website I show 1/16" as standard.
 
jseng1 said:
.042" is only .002" away from ,040". Show me where on my website I show 1/16" as standard.
Click to expand...
1/16" = .0625 - you say both .042" and .062" are std.

Head gasket question for Jim Schmidt or others
 
Parts arrived; thanks Jim.

Head now needs to come off and visit Leo Goff, so reassembly is a ways off but I will report back.

Tx - B
 
Ye Olde ' Copper Coat ' or Koper kote , is pressure sealing anti sieze , so is good on bolts too , particularly the large hollow exhaust ones . both surfaces .

This way you can wash & reuse all the gaskets , if your Scotish .

" I can't kick through the compression stroke when the engine is stone cold "

ahem .

Position the pistons up around t.d.c. , rolling in gear if neccesary . Then position the kick start engaged , at The TOP of the thigamy .
Kicking it into engagement is coarse & vular . Leap skyward , leaving your foot onit . It'll start moving - so your legs straight . Your
FULL WEIGHT will throw it over two compressions , just .

Previously , if its COLD . Turn on fuel & tickle carbs . After freeing the clutch - use your weight to turn it though say four compressions .
one at a time - kickstart out so its maximum leaverage . as in square/ perpendicular to yr lower leg . Max. Mech. advantage . old Boy .

Therefore its primed & the oils been spread / worked . So your not doing ten things at once, as it were .


Head gasket question for Jim Schmidt or others


Only thing most wotid do , is check piston to valve . wind in adjusters one turn ( 40 thou. ) turn through carefully , plugs out . just in case . Youre likely way clear on a std. cam .

This is the proper way to start an engine . https://www.dhmothclub.co.uk/gipsy-engines-and-the-art-of-propeller-swinging/
 
Matt Spencer said:
Ye Olde ' Copper Coat ' or Koper kote , is pressure sealing anti sieze , so is good on bolts too , particularly the large hollow exhaust ones . both surfaces .

This way you can wash & reuse all the gaskets , if your Scotish .

" I can't kick through the compression stroke when the engine is stone cold "

ahem .

Position the pistons up around t.d.c. , rolling in gear if neccesary . Then position the kick start engaged , at The TOP of the thigamy .
Kicking it into engagement is coarse & vular . Leap skyward , leaving your foot onit . It'll start moving - so your legs straight . Your
FULL WEIGHT will throw it over two compressions , just .

Previously , if its COLD . Turn on fuel & tickle carbs . After freeing the clutch - use your weight to turn it though say four compressions .
one at a time - kickstart out so its maximum leaverage . as in square/ perpendicular to yr lower leg . Max. Mech. advantage . old Boy .

Therefore its primed & the oils been spread / worked . So your not doing ten things at once, as it were .

Only thing most wotid do , is check piston to valve . wind in adjusters one turn ( 40 thou. ) turn through carefully , plugs out . just in case . Youre likely way clear on a std. cam .

This is the proper way to start an engine . https://www.dhmothclub.co.uk/gipsy-engines-and-the-art-of-propeller-swinging/
Click to expand...
ahem

I guess the high compression kick start advice is aimed at me given the quote. I just bump nudge it past the max compression spot with the kick start. Then fire it up. I don't need to free the clutch. The bike has a belt drive dry clutch. No tickling FCRs. Pump the accelerator pump a few times with the throttle. There is no interference inside the engine other than pushing air. With the plugs out it is easy to kick over regardless of where the pistons are in the bores. Also I'm about 8 inches too short to kick the engine over with the kick start straight up. If I were around 6'5" and weighed about 250 lbs, I could probably kick it over past the compression stroke regardless of where the pistons were. I actually can kick it over through the compression if I push myself, but the kick is so limp wristed the pistons barely move more than half a stroke and it won't light up. :)

My point was I have a lot of compression. There is/was a video out there where Nigel can't kick over his 920 because of the compression. Basically, the same thing is happening to me, but with a 750 engine. My 750 engine is not stock by a wide margin.
 
Here are the test results I made with sealers.

HEAD GASKET SEALER COMPARISON





Pliobond darkens & hardens at 450 to 500F and loses integrity at 500 but still stays in place and when its cooled it remains adhered to the metal. Stays adhered at 400 F (the best results so far).



JB epoxy weld good to 450 and still stays in place at 500 but loses adhesion.



Permatex copper “spray a gasket” high temp – starts smoking and loses adhesion at 400 F but stays in place and is still adhered when cooled.



K&W “Copper coat” brush on gasket sealer – loses adhesion at 400 F but stays in place and is still adhered when cooled.



Silicone sealer resists heat up to 500F, starts to fail by 550 and loses its adhesion. Did not harden but has mediocre oil resistance. Silicone leaks oil as a head gasket sealer.



Permatex “Ultra” silicone based oil resistant gasket maker loses adhesion at approx 500F and fails. Minimal hardening. Silicone leaks oil as a head gasket sealer.



“The right stuff” by permatex should have worked but failed in a Norton as a head gasket sealer.



Hylomar AF stays gooey – non-hardening and no adhesion but good to 500 deg. Aerograde Hylomar is semi hardening and has some adhesion (but not much) after drying and is good to about 450 but looses adhesion around 500 and has poor adhesion compared to pliobond at all temps (worse at 500 deg - loses all adhesion permanently).



Wellseal stays gooey – non hardening and has no adhesion, starts smoking at 400 and turns to water consistency at 450F



Gasgacinch Weldwood and Barge contact cements burned black & hardened before pliobond and lose their adhesion at lower temps around 400F.



Permatex motoseal 1 grey (same as popular Yamabond 4) bubbled at 400F and hardened but did not lose its adhesion. Became very brittle but was still adhered when cool.



Yamabond 5 (clear contact cement) bubbled at 400F burned black, became brittle and lost adhesion.



Permatex high tac turns to liquid, smokes and loses adhesion at about 350 F.



Silver paint gets soft and loses adhesion around 350F



Permatex formagasket starts smoking & bubbles and fails at 250 – 300F.
 
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Just thought it might help .

Theres ' cold ' and theres ' cold ' . A few pictures of I.o.M. P.R.s have the twelve foot kickstart lever . Or is that inches . Or a bit more .

Get your point , But your full weight on the footpedal should push it through , was my point . 10 1/2 stone & It took ' a knack ' on * : 1 comp ,
with the mangey 750 kickstart . Always thought a decent straight long one , Not so far out as stock , would be the trick .

Intrestingly ! ! * , 7.5 : 1 C.R. in a 55 race 500 twin Triumph , Running Avgas - on the road , with the manual advance when it lost it ( the advance )
it just about got left ( take the bus ) kicking back , run starting . About the 6th attempt . ( or tenth ) or was it twelve , after being told THAT WAS IT
it did start . Took a few minutes to catch the breath , before the pilot was opperational . ! on a cool evening .

SO , we appreciate High Comp , C O L D , on a 750 , might not be ' a piece of cake ' . Just thought it ight help , perhaps .

Get a gas torch & straighten a late 850 one ? You can see its ' up a way ' .

Ere itis Full Size . ( click on picture to getit BIG . )

BACK to ead gaskets ! . Thanks .
 
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What is wrong with composite head gaskets? They are almost universally used on engines with far more compression than any Norton engine. The only remark you can make on std head gaskets is that the 850 ones are too wide.
 
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