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Post by GrumpyUnk on May 2, 2018 11:28:56 GMT -5
If you look closely at the second picture, you can see past the side of the piston to the top of the compression ring. I think that's a lot of clearance between piston:cylinder wall. You may want to check the specified clearance. If there is too much, you will get the piston rattling around and making noise.
Plop the new piston into the BBK cylinder. See how closely it fits. The ones I have, you can place the piston, let it move to the top of the cylinder, invert the cylinder with a hand covering the bottom of the cylinder, and the piston will slide to the bottom of the cylinder slowly, not with a thunk. That is how close the gap between the two is, at least when they are both new.
If you have a 'clicky' type torque wrench, I have found that on lower torque settings, some are reluctant to make any noise. You have to 'feel' the mechanism release or snap. I heard nothing @15ft/lb doing the same thing you were doing. I didn't know the spec for the two bolts alongside the timing chain chamber, but I think less than 15ft/lb. The bolts felt as if they were already tight enough below that number. Dunno if I missed the wrench 'tickle' or not, but I stopped as it felt they were 'done'.
tom
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Post by cagiva4ever on May 2, 2018 14:25:13 GMT -5
-"But not sure if that is right all oily like that."
What did i just recently tell you about "China blowby" on 139qmb's. memory not that short......
your piston even isnt as "oily" as they usually are, like i said , intervals.....
are you starting to realise why these need regular service/de-carbon work for cyl-head and piston rings....
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Post by diynuke on May 2, 2018 14:46:27 GMT -5
indeed a big gap between the cylinder wall and the piston..
so i guess it's best to disassemble it all. (remember to put a rag under the piston when you remove the c-clip so it doesn't fall down in your engine.)
I have 1 piston which has over over 2mm of play between the piston and the piston pin so yeah it sounded like it was ready to explode.. still ran but well.
just threw on a new cylinder kit and its still running happy now.
So i guess it wouldn't hurt to have a look under there. (you should do that anyway)
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Post by scootnewb on May 2, 2018 16:57:19 GMT -5
"What did i just recently tell you about "China blowby" on 139qmb's. memory not that short......"
LOL. Yes I remember what you told me about the blow by. I was just double checking. I didn't expect it to get that bad after cleaning the combustion chamber / piston and riding less than a mile.
"so i guess it's best to disassemble it all. (remember to put a rag under the piston when you remove the c-clip so it doesn't fall down in your engine.)"
Yes. That is going to happen very soon. The hardest part for me are the G-clips. For real, I have top end assembly and dis-assembly down. Once you do it once or twice it is pretty straight forward and frankly there are Lego sets more difficult to put together.
My biggest problem is physically wrenching. I have some motor issues, (no pun intended) - getting down and back up to remove the bolts on the exhaust would be the second most difficult thing aside from the G-clips. But I am enjoying myself between rage-ing out when I discover a defective part. Unfortunately, if there is something wrong inside the case/block, I am going to have to bring it to the shop.
"If you look closely at the second picture, you can see past the side of the piston to the top of the compression ring. I think that's a lot of clearance between piston:cylinder wall. You may want to check the specified clearance. If there is too much, you will get the piston rattling around and making noise."
Yeah, I see what you are talking about. How strange. I don't see how re-assembling the top end could allow for that be misaligned. It must have been like that all along.
Once I get some more energy, I am going to take off the jug and see what it looks like with the BBK.
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Post by scootnewb on May 2, 2018 17:08:02 GMT -5
If you look closely at the second picture, you can see past the side of the piston to the top of the compression ring. I think that's a lot of clearance between piston:cylinder wall. You may want to check the specified clearance. If there is too much, you will get the piston rattling around and making noise. Plop the new piston into the BBK cylinder. See how closely it fits. The ones I have, you can place the piston, let it move to the top of the cylinder, invert the cylinder with a hand covering the bottom of the cylinder, and the piston will slide to the bottom of the cylinder slowly, not with a thunk. That is how close the gap between the two is, at least when they are both new. If you have a 'clicky' type torque wrench, I have found that on lower torque settings, some are reluctant to make any noise. You have to 'feel' the mechanism release or snap. I heard nothing @15ft/lb doing the same thing you were doing. I didn't know the spec for the two bolts alongside the timing chain chamber, but I think less than 15ft/lb. The bolts felt as if they were already tight enough below that number. Dunno if I missed the wrench 'tickle' or not, but I stopped as it felt they were 'done'. tom Hopefully the piston being like that didn't damage anything.  |
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Post by scootnewb on May 2, 2018 18:54:00 GMT -5
Nailed it!
I would have put on the 50mm jug and piston but it was getting late and by the time I got through fumbling with the G-Clips, it would have been dark.
So I went back to the stock head then set the valves to .05mm. Which is what the plate in front of the seat recommended. I put on a new exhaust, which no matter what, the muffler is rotated a little bit and a block off plate. Fired it up and no ticking coming from the motor at all!
Now it is running well and should be good to ride until I'm ready for another go at it.
I am ready for my own show on Velocity channel!!!
So stoked. BBK goes on Sunday. I need to re-coup from being in the Sun all day.
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Post by GrumpyUnk on May 4, 2018 10:12:30 GMT -5
Do not leave the plastic shrouding off or you will cook the cylinder walls & piston. I have an example set to show the results of doing so if you want a look-see. Piston and wall both scored. The 'genius' that did the work also installed the piston with the IN marking towards the exhaust. Guess the reliefs are not really needed unless you go with a higher lift cam, but to be sure, checking the real gap using some clay would be a good idea.
Sounds pretty good, if you ask me. But, do put the shrouding on. Put the 'gasket' around the head, and the one that slips onto the spark plug boot. Sealing to force the blowing air to actually cool things is a good idea.
tom
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Post by scootnewb on May 4, 2018 12:57:39 GMT -5
Do not leave the plastic shrouding off or you will cook the cylinder walls & piston. I have an example set to show the results of doing so if you want a look-see. Piston and wall both scored. The 'genius' that did the work also installed the piston with the IN marking towards the exhaust. Guess the reliefs are not really needed unless you go with a higher lift cam, but to be sure, checking the real gap using some clay would be a good idea. Sounds pretty good, if you ask me. But, do put the shrouding on. Put the 'gasket' around the head, and the one that slips onto the spark plug boot. Sealing to force the blowing air to actually cool things is a good idea. tom I am going to put the plastic shroud and 'gasket' that goes around the head back once the BBK is in. I haven't ridden it yet since swapping heads. I think I will try the putty on the piston head and see what is going on under there. The Glixal kit came with a dished piston. Yes, please show the scorched piston. |
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Post by GrumpyUnk on May 5, 2018 9:48:15 GMT -5
 ]] This is before removal.  View of combustion chamber and head gasket. I had to use abrasive to make the surface flat again.  A more clear indication of heat eating up parts, particularly the head gasket.  This shows some of the piston scuffing. The cylinder wall was scored, and the rings no longer sealed well for compression above about 50psi. Would not start. The head area towards the chain chamber was below the rest of the surface, as shown in the picture of the engine & chain.  You can see the 'smoke trail leading into the chain case. It now has a 47mm cylinder and runs pretty well. Pulls nicely mid-range, which is what I wanted. tom ADDED: Note the piston:cylinder wall clearance, even on this smoked piston. There's less gap than the image you(?) posted previously. |
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Post by GrumpyUnk on May 5, 2018 10:10:41 GMT -5
 This shows the surface after using 220 AlOx on glass. The dark spots would have taken a lot longer to remove, and I didn't want to up the compression ratio any more. There was a nickel sized depression on the area between the cylinder and chain cavity that was the main reason for re-surfacing. I kept going until it was no longer visible.  If you look closely, you can see where I lapped the valves into the seats. That 'grey' color is bared metal, nice even finish all the way around. The valves looked the same after I got done. I kept the springs, keepers, shims(at the bottom of the spring touching the head), keeper 'washer', all together and the springs up / down orientation the same, and installed new valve stem seals. It now starts like the ones in the youtube videos, at the touch of the key. tom |
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Post by scootnewb on May 5, 2018 23:08:15 GMT -5
My word. That piston is upside-down. I think you mentioned it was. I noticed some piston scuffing on mine too and it has under 200 miles(I forgot the odometer is in km). At the time I didn't realize what the cause was and just thought it was normal. The scoot, when I got it, it seemed the plastic shroud and 'gasket' that goes around the head was never removed. Someone (the owners kid), tried messing with the carb but never got very far.
I should have some pics up tomorrow when it's out with the old and in with the new.
I'm going to change the oil before the bbk install, ride it a bit and change it again.I also have some gear oil. I gotta read up on the oil/break in procedure.
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Post by scootnewb on May 6, 2018 21:39:30 GMT -5
Well it let up on the rain a little bit and I was able to install the BBK. I made the gaps correct in the rings, oiled it all up. The longest part was the G-Clips. After getting it together and adjusting the valves, I put on the fancy new valve cover, connected the battery, cause I broke the kick-starter earlier, drained and put in fresh oil, hit the start button and it started right up. It was already dark out when it came to put the head on but the cel phone flashlight got that sorted.
I adjusted the carb a bit but will do the jet replacement/tuning tomorrow.
Something about the Glixal kit though, the head gasket is thicker than stock. If you use that one, the cam bearings won't sit flush on the rocker assembly. I used a new stock gasket.
It seems all good.
I didn't have many pics of the install. It was getting dark.
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Post by stephanienatasha on Mar 31, 2023 17:30:46 GMT -5
I can't say exactly what the issue is based on your description of the steps you've taken to eliminate the tapping but I might be able to suggest a couple things that may seem like common sense but we're human and miss things sometimes. I haven't followed you in everything you've done to the engine recently but I assume that you tried doing a big bore or simply done a piston swap only to discover that the new piston didn't meet specs and switched back to the original piston. Assuming that I'm understanding everything correctly then I suggest first that you go back over your steps and ask yourself what changed. It could be something that you've overlooked or dismissed thinking that it shouldnt make a difference. For example, Did I replace the cylinder base gasket and head gaskets? Did I forget to put one of them in when reassembling? What there any difference between the old and new gaskets? Were the gaskets the exact same thickness? (could throw your cam & valve push rods out of time slightly but enough to make a difference). Are my valves seating fully? (even a slight amount could cause the tap). Are my rockers correctly alligned with the valves? Are my rocker bearings/bushings within tolerances? Did I reinstall my old piston with the exhaust & intake sides correctly oriented with the cylinder intake & exhaust ports? (Ringns could be hitting the port openings). Did I correctly "Clock" my piston rings accurately when I reinstalled them and could one or more of my rings have slipped out of position during installation? (rings could be hitting ports). Could I have installed one of the rings top-down or upside down? (yes it makes a difference and the rings should be marked from the factory). Finally, Are my piston wrist pin and connecting rod bushings/bearings within tolerance? (Kinda sounded to me like your piston wrist pin may be tapping in it's connecting rod bushing/bearing). Back up a minute and retrace your steps and don't dismiss your sneaky suspicions if you have any because your gut is telling you something. If you have a suspicion then go back and check it out and you'll likely be right. I can't really say what's going on but I'm sure you'll find it. Oh, do check the valve cover, head, and cylinder with a mechanics stethascope (can spell, Duh!). It may help to isolate the problem when you know precisely where to look. Often sound seem to be coming from someplace but are actually coming from someplace else and once you discover the precise source of the ticking you'll be better armed to address the problem. Like I said, I can't resolve your issue but maybe I've nudged you in the right direction. Good luck.
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