I still have some fine filing to do, but it looks like a much better mating surface than before. Do I still need sealant? I've read conflicting things about sealant with metal gaskets.
Looks good! I wouldn't use sealant on the head gasket, I would use a small bead around the base and water jacket, particularly if there was leakage in the past.
I would. It's impossible for hand tools to achieve a truly flat surface. A low spot may need sealant to fill the remaining gap. A high spot may lever the rest of the cylinder up and need sealant everywhere else. The gasket can accommodate some surface irregularity, but not much.
If I do use sealant, where should I apply it? Around the entire base or just this water jacket? And under where the gasket will sit, or on the inside perimeter of it?
A metal gasket wants a flat surface... like -/+ 0.001" flat.
If you don't think you've got it PERFECT, you can run a paper gasket, where you're allowed a larger deviation... and if you use a paper gasket, use a sealer.
A metal gasket wants a flat surface... like -/+ 0.001" flat.
If you don't think you've got it PERFECT, you can run a paper gasket, where you're allowed a larger deviation... and if you use a paper gasket, use a sealer.
If he scraped it he could get it much flatter than that but it seems like a lot of work. I guess he could could go half way and use a known true surface and bluing to get him close.
This is the base gasket, not the head gasket. Make sure your JB Weld job does not have any high spots. Sealant around the coolant passage (and on both top and bottom of the gasket), nowhere else. Thin stripe of sealant only. Apply the stripe of sealant directly centered on the embossed part of the gasket - it will squeeze out and fill where it needs to from there.
A metal gasket wants a flat surface... like -/+ 0.001" flat.
If you don't think you've got it PERFECT, you can run a paper gasket, where you're allowed a larger deviation... and if you use a paper gasket, use a sealer.
I'd agree if this were a headgasket on a race motor, KTM asks for Max. distortion: 0.05 mm/.002". But it's not, it's a thumper's cylinder base gasket and the spec is so wide that it isn't typically given in a service manual. A gasket from an old sock and some bubblegum would probably work fine.
The challenge here is making the water jacket leakproof and to a lesser degree not altering compression. The steel gasket is probably something like .020 thick and has a vitron seal painted around the water jacket area. It's unlikely the vitron would have sealed the corroded-away surface, so he'd have been back at the cylinder in no time with another leak. Filling and truing a small divot to within .005" is reasonable for a backyard mechanic with a file - that's close enough to work on a head gasket by KTM specs. In this case it's only sealing 20PSI his cooling system 25% above when his rad cap blows.
The bike was leaking coolant before, it corroded the area on the case mating surface. If he didn't fill the void, he'd be relying on soft sealant to fill a gap and hold back 20PSI. Might have worked, but considering the fill and file is a lot less work than tearing off a cylinder, I think it was the right move.
I would. It's impossible for hand tools to achieve a truly flat surface. A low spot may need sealant to fill the remaining gap. A high spot may lever the rest of the cylinder up and need sealant everywhere else. The gasket can accommodate some surface irregularity, but not much.
Years ago my dad had watchmakers at his business, I sometimes got to go into the shop. An old watchmaker used to challenge me to duplicate watch parts with a file. I could file a raised repair across a true surface a good file, well within .001".
After gathering info from a number of people, including you guys, I think I am going to run a thin layer of Hylomar on the gasket. I might also get a sanding block and 1000 grit and wet-sand the surface as smooth and even as I can get it first.
After gathering info from a number of people, including you guys, I think I am going to run a thin layer of Hylomar on the gasket. I might also get a sanding block and 1000 grit and wet-sand the surface as smooth and even as I can get it first.
After gathering info from a number of people, including you guys, I think I am going to run a thin layer of Hylomar on the gasket. I might also get a sanding block and 1000 grit and wet-sand the surface as smooth and even as I can get it first.
It looks fine to me this is not a critical mating surfaces that needs polishing. If you place a steel rule across the fix and you can't slip a sheet of paper between the base and straight edge you should be good.
DO NOT use sandpaper there! At this point I think another matter needs to be pointed out. You absolutely MUST get all trace of dust and debris that may have arisen from filing or sanding out of the interior of the engine.
As long as there aren't any high spots in the JB Weld that you can feel, it's fine with a stripe of sealant around that coolant passage on both sides of the gasket. Don't apply a coating everywhere on the whole gasket. Excessive amounts of sealant can end up getting into places that you really shouldn't have it - like oil pump inlet screens, oil passages and jets inside the engine, etc.
OK. Not a great idea to use sand. It was just recommended by another person who said to make sure that the sanding doesn't go anywhere into the engine. Thought I'd run it by here to get a 2nd opinion at least.
The filing that I did was minimal based on the recommendation in this thread. I made sure to remove most excess and smooth out the surface when applying the JB weld for this reason. I will take the compressor to it when I am done and blow out any debris though.
It looks fine to me this is not a critical mating surfaces that needs polishing. If you place a steel rule across the fix and you can't slip a sheet of paper between the base and straight edge you should be good.
if you change the base gasket be sure it is the same thickness as the one you are replacing. if you go even a few thousands inch thinner it will draw the piston higher up the cylinder at top dead center that same amount. being a used engine you may have an untouched un-noticed wear ridge at top of the cylinder - don't let a change in gasket thickness drive your top piston ring into it. this could cause some damage to the top ring.
Thanks! Although I am not overly confident. I don't really know what I'm doing. If I manage to get it running again I'll most likely try to get it on the road next spring. Just finished school and insurance and gas ain't cheap! But, not going to lie, it's been 4 years and I'd love to take it for a ride this summer.
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?
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