Barrel Base Gasket?

Brooking 850

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In the manual and parts catalogue for the 850, there is no mention or diagram of a barrel base gasket although there is one in every gasket set that you purchase.
I use one in my race bike with the high comp pistons to control deck height, but what about the standard flat top pistons?
Manual says to apply some sealant , no mention of the gasket.
What do the experts say?
Regards Mike
 

robs ss

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Well, you've asked for expert advice - not my territory, but I'll relate what I'm doing to my 650ss (spigotted barrel, flat top pistons).
In the 650ss (as with all pre-850 heavy twins) that joint is probably one of the most highly stressed on the bike - not having the long side bolts.
I decided to not fit a base gasket but:
1. Decked the crankcase mouth to flat
2. Spent a few hours with a scraper and files (and engineers blue) on the bottom face of the barrel reducing maximum gaps from .008" to .0015"
3. Will be using Loctite 518 - designed for gasketless joints between cast iron and aluminium (discussed with Loctite tech help)
I'm sure there will be many contrary opinions but..

Good luck Mike
Cheers
Rob
 
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Brooking 850

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Thanks Rob, sounds good, i have only 1 x base gasket left in my meagre stocks and need that for the race motor.
So looks like the road bike will get no gasket.
My preferred gasket goo for this area and cases is 515 the purple one.
Is 518 red in colour?
regards Mike
 

robs ss

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is 518 red in colour?
Yes it is - I was going to go with 517 (which I already had experience with and still had some left) but the tech advice was to use 518.
Regards
Rob

ps: Just looked at the tech blurb on 515 and it appears good for the application (all three - 515, 517, 518 are anaerobic for flanges - 518 just specifies the metals either side)
 
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Brooking 850

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Just looked up both product specs, they are very similar in what they are generally used for , ie machined metal faces/flanges and all metals.
Regards Mike
 

robs ss

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I see both are apparently good for joints up to .010" - I chose to reduce the gap to be well within "safe" range.
 

Fast Eddie

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Mike, I know that some 850s, at least mk11a’s came without a base gasket. The stock CR is already low and there is bags of room between the pistons and head / valves etc. All you’re going to achieve by using a gasket is to throw away a little more precious CR...!
 

Brooking 850

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Thanks Nigel, yes I had it the back of my mind I would go with out it, then after I wrote on here, I loaded the pistons into the barrels, up ended the barrels and installed the gudgeons, so too late , all done without the gasket any way !!!!
I had to true the top of the barrels, it took close to 0.004" to get them right, probably the reason the HG blew in the first place. Humps and hollows.
So a bit of extra CR as you say, the pistons only just get to the top of the bore , and thats without the HG and head squish, so plenty of room.
Make the best use of pump 98 fuel.
Mine is a Mk 1 A 1973 Silver barrel model
Regards Mike
 
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L.A.B.

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In the manual and parts catalogue for the 850, there is no mention or diagram of a barrel base gasket although there is one in every gasket set that you purchase.

Manual says to apply some sealant , no mention of the gasket.
Loctite "Plastic Gasket" was the original specification for the 850, however, a base gasket was used on the 850 Mk3 which is why it is included in 850 gasket sets and it can be used on the earlier 850 models.

https://andover-norton.co.uk/en/shop-drawing/123/engine-cylinder-cylinder-head#

https://www.accessnorton.com/NortonCommando/norton-villiers-loctite.17953/
 
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SteveA

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I have never used a base gasket, all the way back to '75. They didn't use them on most 850s. Use Threebond or similar.

I race with 98 pump fuel, running around 10.5 compression ratio, so would not expect any problems there.
 

Brooking 850

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Thanks Les, yes that exploded view on the AN site is the later model as earlier manuals dont show the gasket.
Loctite 515 it is this time job done
Regards Mike
 
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74 850 MkII USA no base gasket. I have had zero problems with base leak.
Only used Wellseal.
 
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Same method as i use Onder also no problems to report . and to me it seems like there is less of a worry with base gasket compressing slightly , and not being able to retorque the through bolts , without taking the head off .Not that i could be bothered !!!!
 

KiwiNeill

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I use Permatex Ultra Grey on everything that doesn,t use a gasket including crankcase, carb flanges and base of barrels, a 6-8mm stiff brush to apply in an even fashion and it gives you plenty of time to assemble.
Just fixed an irritating and elusive leak from my Mk3 primary case, was oil coming through the (reasonably firm) alternator wire grommet and hole. Cleaned with kero and brake clean, filled grommet and hole with Ultra Grey and left overnight.
No leaks.
 
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I'm about to install my 850 MK3 barrels that have been honed and still standard bore .. Question is how to apply the 518 Loctite to the barrels and block .. Is a light smear enough on each surface or a thicker smear .
Cheers
Fred
 
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You can use a lot as the excess will not set, I run a small bead and let it spread itself on assembly, as long as the bead is continuous it will seal.
 

freefly103

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I did install a base gasket on my 750 but removed it shortly thereafter as it blew out at the oil drain hole between the barrels and cases. Used permatex. No problems since.
 

concours

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I'm about to install my 850 MK3 barrels that have been honed and still standard bore .. Question is how to apply the 518 Loctite to the barrels and block .. Is a light smear enough on each surface or a thicker smear .
Cheers
Fred
I smear a relatively thick, even coat. Think .020” thick, (not that that much is needed, but it ensures no “holidays”) enough to see the red tint. As mentioned, anerobic, so no “snot string” danger like RTV.
 
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