Massive leak from right hand kips cover during leakdown

[JZ05220r]

Hey guys. I just got my 220 engine fully assembled and did a leakdown test. It’s practically holding no pressure and I found the leak on the right hand kips cover where the advancer shaft connects to the paw gear. I just pulled the top end and replaced the seal for the main shaft again. It didn’t help. I have no idea what to do. I did just realize I didn’t position the piston in any particular position, maybe that played a roll but I’m calling it a night. UPDATE: couldn’t get it out of my head and performed the leakdown with piston at tdc. No change.

[Molly's 70]

did you replace the seal behind the shaft?

[John_S]

I wonder if the packing oring has anything to do with it. I know you were looking for a new one. What did you end up doing there?

You said fully assembled but asking anyway. Do you have the kips cover with rubber boot installed on the right side and the slotted cover installed on the left? I failed a leakdown before because of slotted cover oring.

[JZ05220r]

I wonder if the packing oring has anything to do with it. I know you were looking for a new one. What did you end up doing there?

You said fully assembled but asking anyway. Do you have the kips cover with rubber boot installed on the right side and the slotted cover installed on the left? I failed a leakdown before because of slotted cover oring.

Yes I replaced the packing with a fresh one. The o ring for the slotted cover is new as well as I have had leak there in the past.

[John_S]

I’m real sorry to hear this. Everything I’ve studied about leakdown tests are done with the piston at bottom dead center. But tdc or bdc won’t affect what’s happening with your engine.

[JZ05220r]

I’m getting to the bottom of it. I think. I never polished the sub valve shaft bores and noticed they seems a bit crusted/oxidized compared to my other cylinder. I’m only going to worry about the one in question. Got a bunch of these polishing bits in assorted shapes and sizes. and will go at it for a bit and see how it smooths out. I believe it is in fact the packing seal that isn’t sealing well because when I took the subvalve shaft with the packing out and greased it excessively and retested for leaks, the needle dropped a bit slower as the grease contained the pressure better than the 2 stroke oil I used upon assembly

[JZ05220r]

I cleaned up the bore the best I could. I then decide to test fit the right hand side subvalve shaft. I test fitted it on both my new to me, and old cylinder. The old cylinder was a much tighter fit. Now I need to figure out a way to either make the oem packing seal bulge out further from its groove to create a better seal or switch to a different o ring all together. Any ideas would be appreciated. Thank you. I attached a picture of the shaft just for a visual of what I’m talking about in terms of the groove.

[JZ05220r]

For the oem packing seal , I am getting wall thickness: 1.3mm, height: 2mm, OD: 8mm. ID: 5.4mm.

[JZ05220r]

The bore for the subvalve shaft is very smooth and shiny on my old cylinder, this one is weathered no matter how much I polish it. Let alone the fact that the bore is bigger to the point it won’t hold air with the stock packing seal. I just made a huge mistake putting all of this money into this cylinder. A thousand dollar mistake. I’m probably going to be throwing the stock cylinder back on and putting the bike up for sale if I’m still not happy with the way it’s running. Based on measuring the cylinder bores on each cylinder I can at least use the new piston on my old cylinder. Quick question.. I have a 69mm flex hone that came with the bike. Is this ok to use on my old cylinder to make sure I at least get a good ring seal? I have to stay positive and consider this a learning lesson.

[KDXGarage]

I would just use some light oil and a green Scotch Brite pad to de haze a cylinder. For true cutting, a diamond hone is needed.

[JZ05220r]

I would just use some light oil and a green Scotch Brite pad to de haze a cylinder. For true cutting, a diamond hone is needed.

Got it, looked into it a bit, thanks.

[KDXGarage]

That's wild. Is there a way to just put a larger, but slightly shaved down gasket / o-ring in there?

[JZ05220r]

That's wild. Is there a way to just put a larger, but slightly shaved down gasket / o-ring in there?

As far as I can tell no. And I’m not sure how it would seal compared to my other cylinders nicely polished subvalve shaft bore. I’ll take any suggestions to make it work but as of right now I’m not sure it’s gonna pass the leakdown test with out a tight seal along a polished surface. I wonder if some type of firearm barrel restoring kit would at least smooth it out enough for me to move on and find an oversized o ring, or even an x ring. I found that brush research makes a 8mm flex hone that might clean it up decent. I’d then need to figure out a way to bring it back to a polished finish.

[JimmyB]

Do you have a local seal or auto supply store that carries a good selection of o-rings, might be able to get the metric one in larger OD. possibly try a 3/16" id in different OD also, customize to fit the bore, you could always shave down the sides if too wide for the grove.
BUT I'm just wondering, once all the KIPS covers(resonator,center valve ETC.), those KIPS rod bolts/gaskets ETC. are installed and the engine is complete, I don't see that o-ring causing a loss of pressure, even if that o-ring was missing the engine should be externally sealed and hold pressure? Piston location(BDC,TDC ETC.) should also not make a difference.

[JZ05220r]

The rubber boot on for the governor lever isn’t designed to be perfectly air tight. All the air is escaping past the packing seal and escaping out of the boot. I appreciate your suggestions. Thanks

[JimmyB]

I agree the boot is just there to keep the kips gov shaft, gears ETC. clean. You shouldn't have pressure from the leak down test escaping into this area. Do you have the seal on the center shaft part # 13107-1324 , seal part # 920499-1238, is this the seal that is leaking or the packing(O-ring) part #49049-1076 on front RH Rod part #46102-1384?

[JZ05220r]

All seals are new. I replaced the center shaft seal twice as I was hoping that was the culprit. After adding lots of grease to the packing seal and bore I noticed the pressure on my leakdown tester dropped slightly slower than before. Totally unacceptable leakdown test results regardless.

[JimmyB]

Is it leaking mainly from that center shaft seal, using a soap/water mix over the motor showing where the leak is coming from? Is the shaft worn, does that seal have a spring on the inner lip? I know some of the smaller ones sometimes don't, sorry I don't recall if it did.

[JZ05220r]

Is it leaking mainly from that center shaft seal, using a soap/water mix over the motor showing where the leak is coming from? Is the shaft worn, does that seal have a spring on the inner lip? I know some of the smaller ones sometimes don't, sorry I don't recall if it did.

I don’t believe there is any wear on the center shaft. I can check with my caliper but it feels smooth for sure. I didn’t check for the spring but I will take a look at that as well.

[pumpguy]

Here's something I would consider if I had this problem.

First, see if you can find the ID of the bore in new/unworn condition. You may be able to use your old cylinder for this.

Take both of your cylinders to a machine shop and explain your problem. Ask them to measure the IDs of both bores and ask if they can sleeve the oversize bore down to the bore on your old cylinder.

If I'm understanding this problem, this should be an easy fix for any decent machine shop.

Worth a try anyway.