Installing Pistons in cylinders (2010)

Hi all, it's my first post here; I have been posting on a couple of other sites and was told about this one so here I am!

Anyway, I have just completed a top end - overhaul and new rings and I have a question - I tried a search but didn't see anything about this. Though that could be due to my poor searching...(I also posted this question on one of the other sites).

THe 850 service manual shows the method for installing pistons in the cyls using two ring compressors and the cyl is pushed down onto the pistons. I read a procedure elsewhere whereby the pistons are inserted in the bores first and positioned where the piston pin boss is below the bottom of the bore; then the cyl/pistons is held above the crankcase on blocks or whatever; then the crank is rotated up and the rods attached to the pistons. THis sounds workable - especially since I only have one ring compressor.

Has anyone used this method and if so, would you recommend it? If not, Sears is up the street and I could buy another ring compressor tomorrow if I had to...

I much prefer installing the pistons into the cylinders on the workbench (install the "inner" side circlips into the pistons, then blocking up the cylinder with a wood block or the like on the cases (or have a helper hold the cylinder in place) while you install the wrist pins and second ("outside") circlips. I've always found that MUCH easier. And yes, then you only need one ring compressor....

Nice pics of this technique here (scroll down a bit). 850mkiia-rebuild-underway-t5086-30.html

B+Bogus is more skilled than me, though. I would not attempt to put those circlips in without wrapping rags around the rods to block off the crankcase mouth. I would surely send at least one circlip into that gaping mouth....(Did I mention I always buy six circlips for each four needed to do the job?)

If your ring compressors are the Lisle type which don't come apart, you will have to insert the pistons into the bore first and then attach the conrods.

I have used both methods, but prefer to attach the pistons to the rods first and lower the cylinders over the pistons. I find it easier to manuver the cylinder than fiddle with lining up the wrist pins while balancing the cylinder and pistons. Both ways work, and I'm certain others find the opposite easier.

You can also make your own ring compressors from a piece of plastic oil bottle and screw type hose clamps (jubilee clips).

I've tried it both ways, and have never been successful following the workshop manual's method. I've always found it easier to insert both pistons into the cylinders and then support the loaded cylinders over the cranlcase while I attached the pins and circlips. I've always done this with the engine on the bench, so I can't really speak to the ease of this method with the engine in the frame. Different strokes, I suppose. I came to this method after much whining to Fred Eaton at Old Brits, who told me that he did it this way. Needless to say, it is critical to insure that the pins fit smoothly into the pistons and little end before the method is tried.

MexicoMike said:

Hi all, it's my first post here; I have been posting on a couple of other sites and was told about this one so here I am!

Click to expand...

Someone must have been quite persuasive. :mrgreen:

Welcome and soon you'll find this is the only place for Commandos.

Within an hour you had all the answers you needed.

Whazzup Mike? Come over from BritBike? A few of us hang there as well.

I guess it's a personal choice, but I've aways done it per the manual. For ring compressors I use hose clamps wrapped around a thin piece of aluminum. It helps to support the pistons from underneath with a piece of 3/4 plywood like this:

mike
I do the pistons in jug method also. I block up the jug with 4 of the long cyl head nuts (the ones under the exh ports) on 4 of the studs. if you wanted to get real trick you could even put old studs in the old style nuts to stop the jug from moving about on the nuts. the fun part is installing spiral lock double wrap pin clips

Really excellent stuff guys, I'm very impressed...maybe I'll delete those other bike links!

I'll let you know how it goes.

Now maybe you could bring the other Mike over, LOL. Welcome Mike. This forum is more active than others and also has a lot of guys that share info. freely, It also seems to be one of the more civil ones I have been on. But you know the rules, No oil threads or tire threads, LOL LOL. Chuck. :lol:

"No tire threads"

You mean we've got to use slicks??

"tire threads"

hee hee

My dear old Dad use to use that term; he also referred to the "Arctic Thundra" (tundra), seriously. UT engineering grad, extremely well-spoken otherwise. I often wondered it he said it that way on purpose, becasue we'd reply using the correct "tread" (tire tread), and he'd continue the conversation using the word "thread".

I sure miss him, thanx for the memory.

I use piston ring compressors, cheap ones from RGM so not worth making them yourselves. If you are doing a top end job then disturbing the wrist pins and circlips is just something else to F**k up when you re install them.
Always found the Manual method easy, tried the other method one time when I'd lent my compressors out to a friend and found it a RPITA.
Take the path of least resistance my friend!

I've only used a ring compressor maybe once in my life. I have a piece of wood cut to restrain the rods though. I just hold the rings with my fingers and slip them home. Works well for me. I normally do them in the frame with the pistons on the rods. Shop towels in the crank openings of course. I did my DRZ the other day and was miffed that I had to take the piston off the rod to get it in the cyl. I do four cyl bikes the same way. Blocks to hold up the cyl are helpfull though.The easiest way would be on the bench though if you have it out anyway.

BrianK said:

B+Bogus is more skilled than me, though. I would not attempt to put those circlips in without wrapping rags around the rods to block off the crankcase mouth. I would surely send at least one circlip into that gaping mouth....(Did I mention I always buy six circlips for each four needed to do the job?)

Click to expand...

Posed shot, after the event
The pliers positively hold the circlip on the plier pins (very slightly flared end...), and my dainty pinkies keep the clip in the right place before letting go. Haven't lost one yet, but plain wire ones are definitely a rag in the crankcase job.

Blue Point circlip pliers...highly recommended

Hortons Norton said:

Now maybe you could bring the other Mike over, LOL. Welcome Mike. This forum is more active than others and also has a lot of guys that share info. freely, It also seems to be one of the more civil ones I have been on. But you know the rules, No oil threads or tire threads, LOL LOL. Chuck. :lol:

Click to expand...

I recognize several of the names here from Britbike. I don't do anything with that one anymore. This one is more to my tastes. I also post on triplesonline.com and the Velocette Yahoo group. Nobody seems to get banned on this one, or insult each other. Good folks!

Well said, Great guys and gals with nothing to prove. We all just try to help.

Oh I was thinking of Jim, I must have confused his last name with the ball player from Philly, LOL.

Got the cylinder installed. I ended up doing the alternate way although actually I tried it both ways unsucessfully at first.

Initially I tried the alt method, installing the pistons in the bores on the bench and then trying to insert the pins with the cyl on some supports above the crankcase. The problem was I couldn't slide the pins in at all even though I had frozen the pins and heated the pistons. The pins would push in by hand maybe 1/2 the depth of the outside boss before becoming too tight to move. This was well before the point at which the pin would get to the con rod so it was not mis-aligning with the rod. So I took the cyl back to the bench and removed the pistons.

Then I attached them to the rods, pressing the pins in place with a padded C-clamp/correct size socket and tried to set the cyl in place but there was no way I could work the rings into the bores while it was on the bike.

SO...I went back to the alternate method and just accepted the fact that the pins were not going to just "hand-push" in place so I started them by hand and then tapped them lightly into place with a small plastic mallet/drift. Worked fine and now the cyl is in place and "torqued" down. I insured the rocker box passage was clean by keeping the pipe cleaner in place as the cyl was placed in position and then cleaning it out with several pipe cleaners dipped in lacquer thinner and then blowing it out with comp air from the timing cover side of the passage.

Really appreciate all the great advice! We're going out of town tomorrow for the rest of the week so I'll install the head when we return next weekend.

Should have attached the pics to my post, above but I didnt'!

The valve seals were shot - just crumbled hard plastic. Ring seal seemed fine but the engine was showing oil smoke at idle and at coast down/throttle on - indicating valve seals/guides. The valves had a very slight bit of wobble at spec lift. The new Black Diamond valves have no wobble at all in the guides - the guides were not replaced. Examining the seats/old valves, it appears the exhaust valves were not sealing as well as they should. I lapped the new valves in and they appear to be seating perfectly - WD40 in the cyl head does not seep at all past the valves. The compression prior to rebuild was 140/135. I'll be interested to see if there is any change . With all the carbon deposits on the head/pistons I'm not sure the better sealing will show much difference since most of that carbon is now gone. What is left is discoloration - I couldn't get it out no matter what I did but you can't feel it at all with a fingernail...

Before/after:

Nice work Mike. What did you use to clean off the carbon?