Your advice about whether to use a crankcase to cylinders gasket or not on my 1973 850

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DennisMo

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I will soon reassemble with rebored cylinders and the place I buy parts from recommends a gasket between the crankcase and cylinders.
When I pulled it apart there was no gasket, just a very hardened dark sealant that was possibly a Permatex Hi Tack type. It did work as there were no leaks.

My inclination is to not use a gasket above because it cannot be retightened once the head is on.

Also, for sealant for the crankcase to cylinders, with or without gasket, I thought to use Loctite 510 that says it seals gaps up to 10 thou and is rated up to 400 degrees.
My parts supplier recommends Permatex ultra black which is rated to 400 degrees. And then there is permeated Hi Tack that is rated to 500 degrees.

I would appreciate your thoughts and patience and I am grateful as this is my first reassembly

Dennis
 
DennisMo said:
I will soon reassemble with rebored cylinders and the place I buy parts from recommends a gasket between the crankcase and cylinders.
When I pulled it apart there was no gasket, just a very hardened dark sealant that was possibly a Permatex Hi Tack type. It did work as there were no leaks.

My inclination is to not use a gasket above because it cannot be retightened once the head is on.

Also, for sealant for the crankcase to cylinders, with or without gasket, I thought to use Loctite 510 that says it seals gaps up to 10 thou and is rated up to 400 degrees.
My parts supplier recommends Permatex ultra black which is rated to 400 degrees. And then there is permeated Hi Tack that is rated to 500 degrees.

I would appreciate your thoughts and patience and I am grateful as this is my first reassembly

Dennis
Click to expand...
Loctite 518.
Designed for that type of joint.
I've used it for 40,000+ miles.
 
I use a Cometic base gasket in my MKIII. Since you have a fresh rebore it should not affect anything in there. No sealer required, and should come apart easily if you need to get in there again. Not sure about the thickness, but I doubt it will change the CR much. I think .010" equals about 1/4 point. Unless you are trying to get every ounce of CR out of the motor it is an easy way to mount your cylinders and no fear of clogging the drain hole with goop.
 
I have always used a gasket as well. Yammy bond that i use to seal my crank cases together, in near 50 years have never had a cylinder to crank to ever leak, but using sealent only a lot do it this way, but i have always done the gasket and Yammy bond ways in my rebuilds as well the few other Nortons i have rebuilt over the years for others without leaks, i have alway used a gasket as it came from the factory with one.

Ashley
 
Fast Eddie said:
I’ve never used base gasket on my Nortons.

For goo, I use Wellseal.

I agree that the lack of ability to re-tighten the through bolts is a concern and therefore making it a ‘hard’ joint is better.
Click to expand...
Nigel,
I agree about the "hard joint" idea. You have a lot more HP and definitely run your motors harder than me. I went with the gasket per Comstock, I have over 15k miles on that build and things are working out well. I used 12 point hardened nuts and they have not required any tightening at all. Obviously I couldn't check the through bolts, but they are Comstock 'waisted" SS bolts. Hopefully I haven't jinxed myself :rolleyes:

Pete
 
Permatex 27036 Optimum Grey Max Torque

Grey so if applied sparingly is not visible without getting very close to the engine. inches close.

Good to 700F degrees. Disassembles easily, but definitely holds things together.

I use it on the crank case and under the Molnar through bolted cylinders on an over 10:1 compression 750 engine, and if it were going to leak it would be leaking.

Just an example of something that works under pressure, vibration, and heat.

Edit: Thin paper gaskets also work if everything is flat and not scratched up.
 
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4 engine rebuilds. Base gaskets from the Andover Norton gasket set, super thin smear of three bond(same as Honda and Yamabond) on both sides. No leaks
 
That gray Permatex stuff is outstanding in the no leak department. However I found it glues things together
and easy disassembly was not the case in my situation. Just a heads up, perhaps it was just me.
 
"When I pulled it apart there was no gasket, just a very hardened dark sealant"

Although I'm not a Norton Historian, the O.P's bike, a 73 850, my '74 850, and it is my understanding the pre-MKIII 850's used no base gasket.
That .023" of assembled height matters.
Many the well meaning people chiming in with using a gasket are ignoring the fact it would be altering the compression (not in a good way) of the 850 as it was built.
 
Schwany said:
Permatex 27036 Optimum Grey Max Torque

Grey so if applied sparingly is not visible without getting very close to the engine. inches close.

Good to 700F degrees. Disassembles easily, but definitely holds things together.

I use it on the crank case and under the Molnar through bolted cylinders on an over 10:1 compression 750 engine, and if it were going to leak it would be leaking.

Just an example of something that works under pressure, vibration, and heat.

Edit: Thin paper gaskets also work if everything is flat and not scratched up.
Click to expand...
Certainly your success is valid, but with so many other good choices, like anaerobic sealers that are more closely aligned with this application, choosing an RTV product is not my first choice. "Flexible" is not desired here.
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"My parts supplier recommends Permatex ultra black which is rated to 400 degrees."
That supplier recommending RTV is not accurate for this application.


To be clear, I use a LOT of these various products daily.
Right now I'm repairing a hydraulic leak on a new machine, 3 other people couldn't find.
2 day tear down.
My reputation rides on success. Choosing high performance sealants requires that you read and understand the tech sheets, not just the sales label.
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Your advice about whether to use a crankcase to cylinders gasket or not on my 1973 850
 
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concours said:
Certainly your success is valid, but with so many other good choices, like anaerobic sealers that are more closely aligned with this application, choosing an RTV product is not my first choice. "Flexible" is not desired here. View attachment 123159View attachment 123158

"My parts supplier recommends Permatex ultra black which is rated to 400 degrees."
That supplier recommending RTV is not accurate for this application.


To be clear, I use a LOT of these various products daily.
Right now I'm repairing a hydraulic leak on a new machine, 3 other people couldn't find.
2 day tear down.
My reputation rides on success. Choosing high performance sealants requires that you read and understand the tech sheets, not just the sales label. View attachment 123160View attachment 123161View attachment 123162View attachment 123163View attachment 123164View attachment 123165
Click to expand...
You must raise your eyebrows at Luddite’s like me who still use Wellseal then 🤣
 
concours said:
"When I pulled it apart there was no gasket, just a very hardened dark sealant"

Although I'm not a Norton Historian, the O.P's bike, a 73 850, my '74 850, and it is my understanding the pre-MKIII 850's used no base gasket.
That .023" of assembled height matters.
Many the well meaning people chiming in with using a gasket are ignoring the fact it would be altering the compression (not in a god way) of the 850 as it was built.
Click to expand...
Well i brought my 75 850 Commando new and when i started the rebuild for converting it to the Featherbed in 1980 my motor was fitted with a base gasket from the factory and every other 850 motor i have rebuilt for mates all had base gaskets all were pre M111s i have never had one that didn't have a base gasket.

Ashley
 
Deets55 said:
Nigel,
I agree about the "hard joint" idea. You have a lot more HP and definitely run your motors harder than me. I went with the gasket per Comstock, I have over 15k miles on that build and things are working out well. I used 12 point hardened nuts and they have not required any tightening at all. Obviously I couldn't check the through bolts, but they are Comstock 'waisted" SS bolts. Hopefully I haven't jinxed myself :rolleyes:

Pete
Click to expand...
Deets,
I used the exact setup that you did with excellent results for many miles and don’t think you jinxed yourself.
Mike
 
Fast Eddie said:
I’ve never used base gasket on my Nortons.

For goo, I use Wellseal.

I agree that the lack of ability to re-tighten the through bolts is a concern and therefore making it a ‘hard’ joint is better.
Click to expand...
I have never used a base gasket, going back to late '75 on MkIII cases.

These days I use Threebond and keep the Wellseal for where I think a gasket needs a little help or the gearbox clutch actuator cover, in that case to speed the process of removing and refitting the cover at a race track!
 
I use a gasket, slightly overtorque and then put the assembled engine minus head in the oven at 100 C for 30 min. (When the wife is away..) to let it go trough at least one heat cycle. Retorque after cooling. Probably makes little difference.

Edit: I do wrap the engine in aluminum foil to minimize smell.
Wouldn't like to get caught..
 
SteveA said:
I have never used a base gasket, going back to late '75 on MkIII cases.

These days I use Threebond and keep the Wellseal for where I think a gasket needs a little help or the gearbox clutch actuator cover, in that case to speed the process of removing and refitting the cover at a race track!
Click to expand...
Threebond 1184 is great stuff.
 
If all mating surfaces are in good order and level then its Wellseal for me, i use three bond 1184 a lot but have found that when used on this joint future parting them can be problematic
 

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