Cylinder Base Condition

[Brian P]

"Pull the cylinder out from the bottom" Huh? I don't understand. If you have the cylinder head torqued down, there is no pulling anything from the bottom. The cylinder is on top of the crankcase with the piston inside it and connected to the connecting rod, and the head is on top of all that, and when you torqued the head bolts, the crankcase and cylinder and head are all clamped together by those bolts/studs.

Anyway, back to ring gap. New rings, gotcha. What did you do with the cylinder? Any machining or honing? What's the crosshatch look like?

Does this engine use cast iron liners or is it plated aluminium? (Most newer high performance bike engines use the latter but I don't know KTM)

 

[Mad Mike]

I thought I'd ask you guys' opinion on this one.

I started to assemble things a few weeks ago and noticed that the dowels that are used to guide the gaskets were completely mangled and in a baggie with my old piston rings that I got back with my heads after taking them to the machine shop last year. I ordered new dowels since I really didn't want to reuse ones that looked like they were yanked out with vice grips, and just got those in a week or so ago.

I got the new piston rings installed on each piston, used my cheap-o ring compressor to insert the front piston into its cylinder, placed a new head gasket on, reassembled the head and torqued the head bolts in two stages as the manual says.

I was then told that, even with brand new OEM rings on an OEM cylinder, I should be checking the ring gap. The section in the manual states that the ring gaps should be checked for a maximum, but no minimum is mentioned in the procedure. I'm guessing now that the procedure is meant to be for used rings since it also says to check for wear and a maximum gap of 0.5 mm. I had a look through the manual and the tolerance section at the back of the manual does state both a minimum range and maximum ring gap. And I've read that, if ring gaps are too narrow, this could lead to the ends butting up after thermal expansion, inhibiting further thermal expansion which would lead to increase pressure against the cylinder and possibly a seized piston. I guess I assumed that, if anything, new OWM rings on an OEM cylinder with 100,000 km of wear would not result in a ring gap that was too narrow.

I'm gong to do this for peace of mind, but I was wondering if I could just remove the cylinder out of the bottom of the bore so that I don't have to order and purchase a new head gasket ($70 and 7-10 business days). The procedure to insert the cylinder was from the top, and then to assemble the head, but, since I haven't yet attached the head to the base, I was thinking that I could do it the opposite way - pull the cylinder out from the bottom and reinsert into the bottom without having to disassemble the head and replace the gasket. Is there any reason why I shouldn't be doing it this way?

The short answer is no, you can't -- the head bolts cinch the cylinder to the block.

I'd just reuse the head gasket with a light coating of spray on copper gasket.

 

[Brian P]

No problem to re-use a head gasket in an engine that hasn't run since the gasket was first installed. It hasn't been exposed to heat, combustion pressure, coolant, etc. The black coating on the gasket should stay intact when you remove it. If for some reason it doesn't (part of the coating sticks to the head or block and thus needs to be cleaned off) then you need a new one.

I've used the copper spray gasket to re-use gaskets that you're normally not s'posed to, but it shouldn't be necessary in this case.

 

[Mad Mike]

No problem to re-use a head gasket in an engine that hasn't run since the gasket was first installed. It hasn't been exposed to heat, combustion pressure, coolant, etc. The black coating on the gasket should stay intact when you remove it. If for some reason it doesn't (part of the coating sticks to the head or block and thus needs to be cleaned off) then you need a new one.

I've used the copper spray gasket to re-use gaskets that you're normally not s'posed to, but it shouldn't be necessary in this case.

I agree, it's not required.

I use copper spray on all my head gaskets, even when it doesn't appear to be necessary -- Its a best practice thing for me. I've never had a head gasket leak (new or recycled) when using copper spray.

 

[Rockwell]

"Pull the cylinder out from the bottom" Huh? I don't understand. If you have the cylinder head torqued down, there is no pulling anything from the bottom. The cylinder is on top of the crankcase with the piston inside it and connected to the connecting rod, and the head is on top of all that, and when you torqued the head bolts, the crankcase and cylinder and head are all clamped together by those bolts/studs.

Anyway, back to ring gap. New rings, gotcha. What did you do with the cylinder? Any machining or honing? What's the crosshatch look like?

Does this engine use cast iron liners or is it plated aluminium? (Most newer high performance bike engines use the latter but I don't know KTM)

I'm not sure about other engines, but mine has an engine block with a base gasket, on top of which I will mount the head that is comprised of the cylinder section and the top section (with valves, springs, etc.) with a head gasket in between. The head bolts I am talking about join these two sections (cylinder and valve/springs section. This assembly is not yet mounted onto the block, so the piston can easily be pulled out from the bottom (bottom of the piston that will be attached to the connecting rod is exposed). I can easily pull the piston out from here, although I am not sure if there is any reason I should not be re-inserting the piston here since the procedure required me to insert it from the top of the cylinder prior to assembling the head (cylinder section and valve/spring section). I can post a pic is this is still confusing.

I took the heads to a machine shop last year. I paid $1100 to clean pistons and valves, resurfaced, if necessary, and to check the specs. Whenever I allow others to perform work, I Can never be sure if they did what they say they did. This is my first time looking at the inside of a cylinder, so I don't have the experience to know how it should look. I posted photos on another forum before and others said it looks good, and I assume that the machine shop would have alerted me of any problems. I'm pretty sure nothing was done to the bore.

I'm not sure what "liners" are.

 

[Rockwell]

As far as re-using the head gasket, I thought I might be able to since it hasn't been put into service, but I read this on the internets:

Do not reuse them. Gaskets seal by crushing. Once they are compressed and conform to the heads/block, they're done. Two things you shouldn't reuse are condoms and head gaskets.

This seems to be saying that, once compressed, they shouldn't be reused even if they haven't been put into service.