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Post by 190mech on Aug 30, 2020 7:45:40 GMT -5
It looks as if the parts were washed in solvent and have no lube on them..Could have been the steam cleaning action of a coolant leak..Air cooling has a thermal stress problem,Liquid cooling has a coolant ingestion issue,no happy medium!
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Post by 90GTVert on Aug 30, 2020 8:52:54 GMT -5
Yes, everything came apart dry. Normally this runs pretty rich so it's wet with fuel/oil. Not sure exactly what happens if it's just a stuck ring and how much that would play a part. I'm sure I've had one, but don't recall.
My cheap replacement airbox has had a mount crack off and I'm not thrilled with the 3 screw joining of the 2 halves. Could be that it contributed to at least a lean-er condition. It didn't show higher CHT or coolant temps or any real signs of being lean to me though so it may not have been a problem. I'll be replacing the airbox with another cheap one that I have. I need to get another decent one in the future with more clamping points.
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Post by 90GTVert on Aug 30, 2020 10:03:29 GMT -5
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pewpew
Scoot Enthusiast
Posts: 254
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Post by pewpew on Aug 30, 2020 11:08:53 GMT -5
Cant see the pictures Everything looks fine to me and they're hosted on my site as usual. Maybe try refreshing in case the server was down at the time. Oh yeah works fine now. Definetly some water got in there
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Post by 90GTVert on Aug 30, 2020 15:23:41 GMT -5
I cleaned the cylinder and it doesn't look awful, but it doesn't look good either. The top of it worries me a bit. You can really see how jagged the edge is up there now. There's also a small chip in the coating above the bridge. Had a pic, but I must have deleted it. 2 o-ring grooves for studs now connect to the bore o-ring. It looks like the bore or studs are a little off center... just enough to make the walls thin around 2 studs. They were intact in the 1,000 mile checkup, so they broke away at some point. You can see their connection in the uncleaned deck. Hopefully it doesn't cause any real problem. I took measurements of the piston diameter and the bore in multiple spots. The piston is now 0.002" smaller than it was at the 1,000 mile check. Thankfully the bore has not worn that significantly. The bore is 0.0005" larger on average. Taper is about 0.001" with the worst 2 specs. Out of round is about 0.0005". Piston to bore clearances range from 0.006"-0.007". I'm guessing they'll be about 0.004" to 0.0045" with a new piston. I cleaned the crank up a little and looked it over. The big end bearing seems fine. The small end of the rod was polished with Mother's and I think it's alright. I think the most technically correct and likely to be reliable path would be to replace the entire cylinder kit. That said, I think I'm gonna try a piston kit, gaskets and pin bearing and see what happens unless those of you more accustomed to coated kits are shuddering at this idea. If so, lemme know. I'll probably place an order tonight to keep things moving. I'm hoping the erosion and rough edge at the top of the bore won't be an immediate failure since the ring isn't up there. I'll see if I can get another pic of the chip above the exhaust port bridge in a sec.
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Post by 90GTVert on Aug 30, 2020 15:29:32 GMT -5
Here's that chip pic :
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Post by 190mech on Aug 30, 2020 18:32:17 GMT -5
Thats a very small chip,smooth any ragged edges with a diamond burr and run it!
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pewpew
Scoot Enthusiast
Posts: 254
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Post by pewpew on Aug 30, 2020 19:04:16 GMT -5
Here's that chip pic : Cylinder looks just fine to me. The little chips dont do any harm, my airsal 80cc xtreme kit had similar chips around the exhaust port from the factory
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Post by 90GTVert on Sept 1, 2020 12:43:57 GMT -5
The piston and stuff came in. The new piston measures 1.966"/49.94mm. That should give me 0.003"-0.004" clearance. When I put it back together at 1,000 miles with the used piston, it had 0.0035"-0.004" and it ran well up till now so I should be good to go in that respect.
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Post by 90GTVert on Sept 1, 2020 18:13:05 GMT -5
I put it back together this afternoon. When I did the head, I put a dab of Ultra Grey where the stud and bore o-rings meet in the 2 spots that had cracked. Will pressure test tomorrow. Fingers crossed for no leaking seals or cracked JB Weld.
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Post by Kenho21 on Sept 2, 2020 13:02:04 GMT -5
I put it back together this afternoon. When I did the head, I put a dab of Ultra Grey where the stud and bore o-rings meet in the 2 spots that had cracked. Will pressure test tomorrow. Fingers crossed for no leaking seals or cracked JB Weld. I had a similar sealing situation on my small case half and did a dab of gasket maker and it worked for me. I’m sure your dabbing skills are even better than mine and you’ll be good too.
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pewpew
Scoot Enthusiast
Posts: 254
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Post by pewpew on Sept 2, 2020 13:29:06 GMT -5
I put it back together this afternoon. When I did the head, I put a dab of Ultra Grey where the stud and bore o-rings meet in the 2 spots that had cracked. Will pressure test tomorrow. Fingers crossed for no leaking seals or cracked JB Weld. Is it possible that it lost some sealing capability when you machined the head? And have you tried to start it yet
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Post by 90GTVert on Sept 2, 2020 13:57:18 GMT -5
Not quite to starting yet. It passed a leak test and is just now in the scoot. If it starts I'll prob ride it briefly so I can re-tq and actually do a compression test on the running 86cc for a change.
It's possible that sealing ability changed with shaving 0.2mm off of the head. The outer head still sits farther up than it, so it shouldn't be robbing too much clamping force. There are ideal compression specs for o-rings, and that would be altered without also cutting the o-ring grooves 0.2mm more. I have my doubts about that making much difference, but I can't rule it out. The walls of the o-ring bores have not changed in thickness from basically milling. That 0.2mm could have been the straw that broke the camel's back, but I'm not so sure it wouldn't have broke anyway. It looks like the stud o-rings are slightly off center vs the bore o-ring, because there's more material between 2 of them than the 2 that broke.
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Post by 90GTVert on Sept 3, 2020 7:49:00 GMT -5
It's running again and video from the process is up! youtu.be/8l1hkM8CiwoOne of the first comments = "tpr junk only last 1000 miles if your lucky". Guess he didn't notice that I'm almost double that so far.
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Post by oldgeek on Sept 3, 2020 9:14:35 GMT -5
In the inspection portion of the video, it appears to me you can see where the coolant leaked by, at least in one place where the o-rings meet near the cylinder stud. I feel like the small piece of metal that is gone is culprit. An o-ring has to have something to push against in all directions in order for it to seal. In other words, as you compress an o-ring it will try to escape anywhere it can, which will lead to reduced cross section and some loss of seal in the problem area. It's the same old deal. The original design of the motor does not allow for the mods being applied to them. Just a little more spacing of the cylinder studs would help us out a lot. Then we could go with an even BIGGER bore and run into the same problems again.
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