cylinder base gasket ?

Well I am going to use the one I have and run it dry. Can't get the cylinder on right now because I don't have a way to hold the cylinder and compress the springs, local stores don't have anything I can use. I will do it by hand if I can get the wife to hold the cylinder while I manually compress the springs.

I just used a couple of standard stainless hose clamps hooked together. If you are real careful, you can get them all compressed and if not too tight, a quick straight motion will get it all on in a heartbeat. Takes a while to unscrew the clamps when your done though.

I used Hylomar on my base gasket although Mick says to put it on dry.

Dave
69S

Ring insertions in all the 360' twins I've attempted from childhood outboard motors to now a days Cdo's, I've never been able to get both sets of ring in at once w/o a helper. A single SS hose clamp can grab all the rings, IF some of the top and bottom ring extend ~1/2 their width pass the hose clamp, touchy touchy tedious.

Hylomar is the only goop I use any and everywhere now on Cdo's.
REMEMBER, if you change the base &/or head gasket you Also Change the valve train geometry on rocker lifter contact. I'd make that my main reason to guild my choice in what to put in seams. If parts can't be sealed by just good goop and thread then thank goodness for base gaskets. I do not recommend synthetic polymer tread. Cotton or silk don't melt and displace or separate with the heat and vibes plus adheres to the goop which new age treads shuns just like their tube caps.

Cdo's have forces patience on me, to wait over night to do final nip down on cured more firm goop layer that helps trap it rather than moosh most out in a seam that will always be in some shearing motion. When successful one most then deal with stopping the factory fasteners from rusting. I've taken to a spriz of clean wheel paint on the non SS ones.

I've never needed anyone to help me re-fit cylinder barrels (either 1,2,3 or 4 cylinder).

I use a narrow bladed (electrical) screwdriver to push the rings in, I don't bother with ring compressors, but I can't ever remember breaking a ring.

And I would always fit a dry base gasket .

This is what the Commando Service Notes (1979) say about it:

quote
GROUP 2:- Barrels, gaskets and head parts
CYLINDER BASE GASKET: This was deleted from Mk. I and II 850, plastic gasket such as Loctite,
Hermetite RTV or similar silicone compound being used. A gasket was again introduced, part no. 0638
12, on the Mk. III as people filled the oil drain with RTV, causing lots of trouble. Removing the gasket puts
the compression ratio up by approx 0.3 of a ratio, see table. The 850 gasket can be used on the 750 but
not vice versa as the cylinder apertures aren’t big enough. 750 base gasket is part no. NM24249 or
Q67869.
unquote

Could not find an actual official Service Release / Service Sheet about it though.

I used Threebond and no base gasket on my 750 and it leaks. :?

I used a base gasket with Hylomar on my 850, no leaks.

I'm going to fit a base gasket on the 750 the next time I have the barrel off. That's going to be sooner rather than later because it seems to have blown the headgasket.

Debby

Debby,
Check that your cylinder bolts are not bottoming out on your 750, especially if you have used new bolts. Mick mentions that in his DVD as a cause of blown head gaskets.

Dave
69S

I couldn't get the bottom rings to go in the cylinder and went to re situate the pipe I had supporting the cylinder and ripped the F*****G base gasket in two spots. There goes another week waiting for a piece of paper, god what a bone head.

I used some blocks of wood on the studs that stick out of the cases to support bottoms of the pistons in near TDC. Three pieces of 3/4" x 6" long (1 X) pine will work just fine. The middle one needs to be a bit narrow to go between the con rods, the outer ones can be almost any width and stick out. I had some old walnut flooring that I used. Oak would work too, even poplar. Softer would probably be better so just common #2 pine.

Dave
69S

Well just to add my two bobs worth. I would not use a paper gasket on an 850, cause you can't re-tighten ALL the cylinder base studs. and fibre/paper gaskets will squish down and need re-tightening. The structure of the crankcase and cylinder assembly would be improved without a potential loose joint union.

If you need or want to keep a lid on compression, you can get various thickness copper base gaskets off eBay. Standard 850 pistons should be 70 thou below the head gasket surface, to keep compression standard.

Cheers Richard