base gasket

[catbed]

do i have to take the pistons out of the cylinder block to remove the cylinder block? because it has roller bearings? if so, does that mean i need 2 ring compressors? and how do i get the pistons back in the block. i know you usually tap them with wood or plastic but from underneath?

ps. meant to change the title but i guess you cant.

[Steve]

The pistons stay with the crank until after you have removed the cylinder block. Yes, you will need 2 ring compressors, but I am sure there is a quick and dirty way to accomplish that.

I have not been that far into an engine, but have read many accounts of it, and I stayed at a Holiday Inn Express last night. 8-[

[hampshirehog]

The bottom of the cylinder liners have a pretty good taper so you don't need ring compressors. Easiest is to get a mate to guide the pistons into the cylinders and squeeze the rings inwards as you slowly drop the block downwards.

If you're doing it on your own I find it easiest to knock up my own ring compressors as the ones on sale here are too deep and won't fit. Cut a strip of thin tin about 1 inch wide and about an inch longer than the piston circumference. Wrap it round the piston and bend the over-lap back. Drill an 8mm hole (roughly that size) through on the now bent back overlaps. Put in a bolt and nut, tighten up your new compressor on the piston so that you can slide it down fairly easly and gently tap the block down, displacing the compressor as you do so.

I haven't got any pics but it's effectively a cheap and rough copy of:

http://cgi.ebay.co.uk/NEW-PISTON-RING-COMPRESSOR-75-80mm-BSA-TRIUMPH-AJSARIEL_W0QQitemZ120082816171QQihZ002QQcategoryZ9946QQrdZ1QQssPageNameZWD1VQQtrksidZp1638.m118.l1247QQcmdZViewItem

[waterman]

I have used large adjustable hose clamps to compress the rings. Buy two and do the inner pistons first, then remove and reuse for 1 and 4. It takes a little futzing to get the tension correct, you want to compress the rings yet be able to slide the hose clamp up and down on the piston. A second set of hands helps when reassembling cylinder block over pistons.

When removing pistons, be sure to block off the large hole to the crankcase to keep the wrist pin circlip from disappearing on you. (Please don't ask me how I know...) Likewise label where each piston goes (keep pistons in same cylinder they came from). Have fun, you can do it.

[catbed]

i dont plan to take the pistons off their connecting rods. i was wondering if there was a way to take the block off without taking the pistons out of it. i just need to replace the base gasket.

[waterman]

It may be possible to leave pistons in cylinder block but would prove to be very very difficult. If you could pull cylinder block up to a point where the piston wrist pin could be removed without pulling rings past bottom of cylinder skirts, it may be possible to do this. Realistically, you will need to pull the pistons out. From there it is remarkably easy to remove pistons from connecting rods (just need to push out wire circlip from groove). I would not hesitate pulling pistons out and off to clean out ring grooves and decarbon tops. Then you can check cylinder for wear also. Yes putting piston back into cylinder block is bear but with patience and a lot of motor oil, they will go back together.

By the way, if this is your 850, it has plain bearings on crankshaft. All of the shaft drive bikes utilize plain bearings. If you are splitting cases, you could separate connecting rods at crank and take pistons out top of cylinder block. I wouldn't recommend since usually top of cylinder has ridge of built up carbon that would play havoc with rings.

[bwringer]

By the way, if this is your 850, it has plain bearings on crankshaft. All of the shaft drive bikes utilize plain bearings.

Nope. Wrong. Dead wrong. Wrong wrong wrongitty wrongo.

1000G/GL, 1100G/GL, and 850G/GL engines have roller bearing cranks.

650G engines are the only GS shafties with plain bearings.

Wanna see?

(Here's the '79 850G engine I rebuilt for a friend this winter. It's for sale in the parts for sale thread, too...)
Image Gallery: http://pix.bwringer.com/v/bwringer/79_850_Engine/



The later GS850 engines are have exactly the same crank.

Here's the GS850 engine I rebuilt last winter:

[chef1366]

Are you sure? :?

[waterman]

My bad..... I blame it on the cold. I am sure Brian is correct. If anyone needs me I will be in the woodshed...

I think I will stay with the 650 discussions, have some experience with them. Again, sorry to upset the masses. Can I hear a "Shafts rule"!!

[bwringer]

SHAFTS RULE!

Now then, to answer the original question...

Whenever the head is removed, you must also remove the cylinders to replace the base gasket and o-rings. These are glass-brittle, and the slight movement will make them leak. And then you're right back where you started.

You should also remove the pistons (very easy at this point), clean them up as advised above, and install new rings and circlips. I've had excellent results using a Flex-hone very briefly (about 5 seconds per cylinder) to freshen up the bores so the new rings will seat. GS850 bores take a very long time to wear out, so unless there's some sort of bad damage, you likely won't need to go to an oversize until well after 100,000 miles.

I've never had any success at all with ring compressors. I just gently, gently, gently squeeze the rings with my fingers to lead them into the bores and work the block down onto the pistons two at at time. No force is needed besides the gentlest of thumps with the heel of the palm. Obviously, this is about 100X easier with an assistant, but it can be done solo.

[catbed]

got the pistons back in without the compressor, and i got the head back on, about to torque it down when i remebered about a bolt that broke off. the one in front of the head.

im not gonna replace the rings or circlips because the bike only has 8k miles on it.