Commando 850 cylinder sleeves

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John Fontenot

John Fontenot

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I have an 850 Commando that will need a rebore. I might need to use sleeves. Does the machine shop bore out the cylinder for the sleeve and do I need to worry about how thin the original cylinder skirts become when sleeve is inserted ? OR do they mill away the old skirt material and let the sleeve become the new skirt ? Thanks for any info on this.


OH, and who has sleeves for 850s ?
Please if anyone has info on this, feel free to be very detailed and long winded. I can take it.
 
You are clairvoyant I swear.... I was just thinking about a future tear down and you answer my biggest question before it was posed. Thank you. Santa Fe is just right out of Houston off 45 making that convenient.
 
you can bore it out all the way to 78.5mm

or possibly to 79mm with special order pistons.

so why sleeve it?
 
jseng1 said:
you can bore it out all the way to 78.5mm

or possibly to 79mm with special order pistons.

so why sleeve it?
Click to expand...
Well, the pistons are siezed in the cylinders so I was thinking ahead. Now I checked the bore size and its 3.03 which I believe is stock. Thats good, there is a quarter sized chip out of the lower skirt of the cyinder but I don't think that will affect anything, what do you guys think ? Is it a bad idea to have the cylinder skirts machined away ?
 
fiatfan said:
What will the cc be if you bore out to 78.5 and 79 mm?
Click to expand...

78.5 mm bore give you 861.5 cc, and 79 mm bore gives you 872.5 cc. On some blocks you can also get away with 79.5 m bore, which gives you 883.6 cc, but this one is pretty iffy, and you really need to check that your particular block has enough thickness for the larger bore. On the other hand, we've been running a 79.5 mm bore engine for 6,000 miles or so, and are very happy with it.

Ken
 
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Are the pistons seized from heat or from sitting for 30-years without being turned over?

If the latter, fill through the spark plugs holes with something like ATF and let it sit. It's amazing how durable the cast iron actually is. It's possible that the a ring is rusted and the kick start doesn't generate enough torque to break it lose.
 
rvich said:
Are the pistons seized from heat or from sitting for 30-years without being turned over?

If the latter, fill through the spark plugs holes with something like ATF and let it sit. It's amazing how durable the cast iron actually is. It's possible that the a ring is rusted and the kick start doesn't generate enough torque to break it lose.
Click to expand...

I may have misunderstood. Not unusual for me. The cylinders have been removed from the cases with the pistons stuck in the bores?

Got any photos?
 
I used sleeves from RGM and installed via Norman White on a donor 850 iron barrel.

Bore was screwed, but also there were sections cracked off of the cylinder spigots.

Sleeves fixed all of that, essentially creating new spigots. The boring for the sleeves burst through the original block material. No surprise there.

But it all seems fine and these barrels are currently fitted to my race bike!

On the other hand....79mm seems worth a try before sleeving.
 
John Fontenot said:
I have an 850 Commando that will need a rebore. I might need to use sleeves. Does the machine shop bore out the cylinder for the sleeve and do I need to worry about how thin the original cylinder skirts become when sleeve is inserted ? OR do they mill away the old skirt material and let the sleeve become the new skirt ? Thanks for any info on this.


OH, and who has sleeves for 850s ?
Please if anyone has info on this, feel free to be very detailed and long winded. I can take it.
Click to expand...

https://www.rgmnorton.co.uk/buy/spun-cast-cylinder-liner-with-spigot-850_174.htm
 
OK, looking at the spigot liners. 850 Commandos don't have spigotted cylinders. Why would that be on there SteveA ? by the way the cylinder is on the case and is seized for being sitting in someone's barn for 30 years with the head off ( I'd like to find that guy and jap slap him). I've had it sitting with ATF for a week and then I tapped on them and added penetrating oil in the bores. Nothing moves the pistons. I'll have to remove the cylinder and the crank from the cases and put them in the press, make a double forked push rod for the press to push both piston out at the same time. Or cut the rods off and do them seperately. Everything else on the engine is great.
 
SteveA, I have a set of barrels that are +0.020" with a bad mark in one bore after a circlip eyelet broke off and dug a hole: Over bore of 0.040" or 0.060 " wont remove the gouge.
Its on my Roadster and am lookig at those RGM sleeves.
Any more info on your RGM sleeves would be appreciated
Regards Mike
 
The link to the liners/sleeves is above.... these are the ones I used, but fitment was done for me, the borer/machine shop Norman uses is I think in Andover or Salisbury! But I think the RGM data is enough.

I supplied the JSM pistons to the process and the installed sleeve was measured and I think honed, to establish the required clearance.

They are spigoted so that the head clamps them in place, rather than have them fall into the crankcase when hot, so, the barrels must be bored for the main OD, then a recess cut for the top section.

Sorry if I though this was obvious, but I also have a set of 920 barrels and 77mm Maney barrels, which if diferent materials/clearances are at least achieved using the same method.
 
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If you have the facilities you may want to try the following: Using a piece of flat stock drill holes in it corresponding to the holes in the head (except the spark plug holes), drill 2 small holes directly above the pistons. Install a zerk fitting it each of the holes. Mount the piece on the engine as you would the head and start pumping in grease via the zerks. Hopefully the pressure will force grease into places that gravity and oil fail to go AND apply enough pressure to free the pistons/rings. If the pistons are at BDC this won't work.
Jim
 
fiatfan said:
What will the cc be if you bore out to 78.5 and 79 mm?
Click to expand...
78.5 mm is approx +.060" which is the largest readily-available overbore piston. The Titanic had to be bored +.040" to clean up the rust seizure scars. One more ovebore and after that, I would consider cylinder plating to save the jugs.

Be sure to tell your machinist to re-establish the bevel on the bottom of the cylinders. It will disappear with overboring.
 
Got the pistons out of the cylinders. Cylinder walls looks way better than I thought, measurement is 3.03 should be stock. I'll have plenty of meat to get to .020 over. Also planning on going with JS Motorsport long rods with the extra light pistons. 10:1 then I'll add a little more thickness in head gasket to get it closer to 9:1 and keep it on regular gas. ( I do have that 1/2'' square chip in the lower cylinder skirt near the relief square cut. I'm guessing that will not affect piston on down stroke ? ) I'll try to get some pics so you guys can see what's up with that. thanks.
 
Re: chip in lower skirt .....

I suffered a piston seizure in my Atlas way back in the late 60's that took a quarter sized chunk out of the skirt at the bottom.

I found a shop that did "metal spraying" which filled the missing chunk. The cylinders were then overbored 0.040. The fix has been in place for about 50K miles.

If you are concerned about that missing chip, check out metal spraying.

Slick
 
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