CMB 90 Liner removal

[ids987]

Hi everyone, just looking for some liner removal tips please. With the CMB Evo style engines, if the liner doesn't pull out easily, I usually use a cable tie in the exhaust port (after removing the C-Clip, but leaving the pin in place), doubled over, and / or across and looped into the boost port; then turn the engine over with spanner on coupling to shift liner. So far this has always worked for me, and I've never caused any noticeable damage.

I started dismantling a 90 yesterday, however, and it's particularly stubborn. Several cable ties in pieces, and no sign of the liner moving.

I guess heat is going to be involved, but it's a AAC P/S set, so liner expansion will be much the same as the case; though i guess the case will get hot first. Also, if it doesn't loosen up much, it's going to be a lot more difficult to try and use physical means on a hot engine.

Might try again with stronger cable ties later anyway (depending on other ideas / suggestions). The ones I used yesterday were cheap ones, and seemed to snap/shear/cut very easily. Any input welcomed !!

Thanks: Ian

 

[Stuart Barr]

Ian,

Use a glow plug washer on both transfer ports. These are soft enough not to damage piston/liner.

Stu

 

[ids987]

Ian,

Use a glow plug washer on both transfer ports. These are soft enough not to damage piston/liner.

Stu

Thanks Stu,

Sounds like a plan.

 

[richard jones]

Hi everyone, just looking for some liner removal tips please. With the CMB Evo style engines, if the liner doesn't pull out easily, I usually use a cable tie in the exhaust port (after removing the C-Clip, but leaving the pin in place), doubled over, and / or across and looped into the boost port; then turn the engine over with spanner on coupling to shift liner. So far this has always worked for me, and I've never caused any noticeable damage.

I started dismantling a 90 yesterday, however, and it's particularly stubborn. Several cable ties in pieces, and no sign of the liner moving.

I guess heat is going to be involved, but it's a AAC P/S set, so liner expansion will be much the same as the case; though i guess the case will get hot first. Also, if it doesn't loosen up much, it's going to be a lot more difficult to try and use physical means on a hot engine.

Might try again with stronger cable ties later anyway (depending on other ideas / suggestions). The ones I used yesterday were cheap ones, and seemed to snap/shear/cut very easily. Any input welcomed !!

Thanks: Ian

I have always used a piece of hard rock maple, 1/2 inch square by 3 in. long, taped on one end from 1 inch from the end down to 1/8 inch on the end of the wood, put the piston at BDC and place the tapered piece of wood down into the liner so the tapered end just barely goes thru the exhaust port about 1/8 inch and the other end rests in the lip of the liner, put the wrench on the collet and be sure to turn clock wise until the liner starts to move, then readjust the piece of wood so it is tight in the exhaust port and repeat turning the collett, when it has moved enough, (!/8), put a couple of flat blade screw drivers on each side of the liner and pry the liner up, change to bigger bladed screw drivers and use pieces of wood on the case to continue prying until the liner is loose enough to remove by hand. I have found when a liner is this tight in the case, it is usually because of excessive heat being generated in the combustion chamber over a long period of time, causing the liner to expand into the case and become extremely tight . Several things can contribute to this condition, number 1 is a very loose piston to liner seal, causing the owner to lean the fuel mixture more to get the fuel to burn with a hotter combustion chamber. there are several other factors that can also contribute to excessive heat such as to much load on the engine, to short of pipe, bearing leaking, fuel delivery starvation from to small of spray bar, to much head clearance, wrong size head button bowl and a few others I have not mentioned.JM2CW ****

 

[ids987]

Hi everyone, just looking for some liner removal tips please. With the CMB Evo style engines, if the liner doesn't pull out easily, I usually use a cable tie in the exhaust port (after removing the C-Clip, but leaving the pin in place), doubled over, and / or across and looped into the boost port; then turn the engine over with spanner on coupling to shift liner. So far this has always worked for me, and I've never caused any noticeable damage.

I started dismantling a 90 yesterday, however, and it's particularly stubborn. Several cable ties in pieces, and no sign of the liner moving.

I guess heat is going to be involved, but it's a AAC P/S set, so liner expansion will be much the same as the case; though i guess the case will get hot first. Also, if it doesn't loosen up much, it's going to be a lot more difficult to try and use physical means on a hot engine.

Might try again with stronger cable ties later anyway (depending on other ideas / suggestions). The ones I used yesterday were cheap ones, and seemed to snap/shear/cut very easily. Any input welcomed !!

Thanks: Ian

I have always used a piece of hard rock maple, 1/2 inch square by 3 in. long, taped on one end from 1 inch from the end down to 1/8 inch on the end of the wood, put the piston at BDC and place the tapered piece of wood down into the liner so the tapered end just barely goes thru the exhaust port about 1/8 inch and the other end rests in the lip of the liner, put the wrench on the collet and be sure to turn clock wise until the liner starts to move, then readjust the piece of wood so it is tight in the exhaust port and repeat turning the collett, when it has moved enough, (!/8), put a couple of flat blade screw drivers on each side of the liner and pry the liner up, change to bigger bladed screw drivers and use pieces of wood on the case to continue prying until the liner is loose enough to remove by hand. I have found when a liner is this tight in the case, it is usually because of excessive heat being generated in the combustion chamber over a long period of time, causing the liner to expand into the case and become extremely tight . Several things can contribute to this condition, number 1 is a very loose piston to liner seal, causing the owner to lean the fuel mixture more to get the fuel to burn with a hotter combustion chamber. there are several other factors that can also contribute to excessive heat such as to much load on the engine, to short of pipe, bearing leaking, fuel delivery starvation from to small of spray bar, to much head clearance, wrong size head button bowl and a few others I have not mentioned.JM2CW ****

Thanks ****, for the info, and the detailed run down. The P/S fit is still pretty good, as is compression. I do my best to keep on the rich side of a good needle too, but the liner has been in the case a long time. Hoping it just needs that initial push to get it moving. I had wondered about hardwood, (actually started searching the house last night for some small strips I remember putting "somewhere safe"). Unfortunately, the main bearing let go yesterday, and there is some relatively minor pitting on the piston crown and head button. Want to get everything apart, clean that up, and also "clock" the crank, check the needles etc. I think (hope), the shrapnel damage from the bearing is minor enough that the P/S will live on for a while. My normal method of getting the liner out is very similar to what you described, just using cable ties instead of hardwood to get the liner raised up those first few mm. I got the cable tie method some years back, from a write up on Ian Folkson's site, but most of the CMBs I've dismantled have been .45 size. Obviously the .90 liner's got that much more surface area, so I guess it needs a bit more "oomph". Even once the liner has moved a few mm, I try to avoid levering with metal if possible. Once it's above the retaining pin, I try to twist and pull manually if I can, going to levers if I need to, but preferably non-metallic, until it's free enough to pull out. Sometimes needs must though.

Thanks again guys for the help.

Ian

 

[SayMikey]

I use popsickle sticks

 

[ids987]

Thanks very much again guys. Good suggestions all round. I think any of these would probably have worked. The easiest to put my hands on were the plug washers, so I went with that one, and it worked a treat. Both bearings shot. The needle roller fell apart when I took the crank out.

 

[tnrcboatracer]

I have bearings for that motor in stock. And I'm sure that Stu does as well.