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#808319 05/09/20 5:49 am
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Just did a top end rebuild on my 72 TR6C, I had to replace the right piston rings which were rusted in. I have it running now but it is smoky on the right side, and there is oil, a small amount of being blown out from the exhaust where it goes into the head. Piston and cylinder both looked fine, ring gaps were around 15 thou, didn't break any on reassembly and bike has done around 12000 miles from new, which appears genuine. Obviously oil is getting into the cylinder somehow, could it just be the rings need bedding in? left hand side is still original rings and work fine. When the head was off I did the valves and didn't see anything amiss either side. I will continue to run as it goes well now to see if it settles, but any ideas?


1968 T150/TR6R
1970 TR6
1970 TR6C
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Did you do the recommended head bolt washer modification to the ones inside the rockerboxes? This stops oil migrating down the headbolts and bleeding passed the headgasket on OIF motors.

Otherwise rings haven't bed in. Did you assemble with some kind of break-in-oil?

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Hi, If you are getting that much oil down head studs into cylinder, you have more problems than just washers.

Remember oil in stud bore must also turn the corner & pass by head gasket.
I’ve seen several motors with oil in stud bores, yet no oil in combustion chamber or leaking outside at head gasket.

Every one I’ve seen leaking to outside or into combustion chamber the head was not flat. Head not bent or bowed, but had dips around bolt holes or between bolts.

I don’t know why some heads get like this or what actually causes it. I’ve seen owners jump through hoops trying to correct this. 100% of time skimming head corrected problem.

Skimming is not to taken lightly, but there is no other practical repair I know of.

Bowed, bent head is a different problem. Straightening is repair for that.

Thicker head gaskets are available if/as needed to make up for metal removed.
Don


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I am going to try to borrow a compression tester to check. I may also pull the head bolts to check for oil & try to seal as a temporary measure to see if there is a difference. Its only on the RH side where I just had to replace the rings so I am wondering if there is something wrong with the piston. easy stuff first though!


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Just checked that thread, all the inner bolts are torqued correctly and haven't had time to loosen as yet?


1968 T150/TR6R
1970 TR6
1970 TR6C
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Did you properly hone the cylinder w/ the new rings?

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Yes it was given a light hone and also there doesn't appear to be any blow by, such as anything coming out of the breather. This makes me think the rings are OK, I didn't notice anything wrong with the piston either, but could be an issue? Compression test should tell me about that when I can. This bike hasn't run in over 30 years and I think there may have been oil residue on the right cylinder side, but can't be sure of that now. I am still going to try checking and sealing the bolts as it is a fairly easy-ish job.


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1970 TR6C
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Well I just took the rocker boxes off, sealed the inner bolts, retorqued the head and put back together. It didn't make any difference so I think it must be in the cylinder.


1968 T150/TR6R
1970 TR6
1970 TR6C
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tiger_cub. -- does the right side smoke immediately or does it have to run a bit before it starts smoking? I like making sure your not "wet sumping" as the cause. Drain the bottom end and measure how much oil is down there. I think 200 CC's is about right? start her up with a empty sump and see if this delays the right side smoke issue--- when I was young and didn't not know about this I pulled and installed my top end 6 times thinking it had to be up there.


59 Bonne (in high school!)--67 TR6c (building)--68 Bonne(building)--69 Bonne (sold!)- 70 TR6r (sold!)-79 TR7v custom (building) - CRF 250x & XR 400 dual sport w/ SM wheels (super fun!) & just bought two Honda CT-90 trail bikes in rough shape!
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Hi tiger_cub, Compression test doesn't tell much when it comes to oil consumption. By that I mean you can have perfect compression & still have oil consumption.

Primary breather motors almost never spit oil like the earlier motor. They can wet sump, burn oil like mad & still not a drop comes out at rear of fender. I've not been able to diagnose problems from putting finger over end of breather hole either. Darndest thing how it works. Sucks sometimes & blows sometimes. Will drip condensation on cold start up in winter. A few to several drops. Water can be slightly oily, but I've never seen liquid oil come out like on the early bikes. They can put a 3" circle of oil on the ground in no time. Seen that several times.

Sometimes the oil smoking diagnosis is determining what's not the problem. Which leaves what the problem is. I hate that!! I want to know & see what's wrong! I've taken many smoking pistons/ring out to see all looks perfect. Yet hone, ring job 2nd time fixes it. Of course this is with straight, round bores. What went wrong?? A mystery to this day.

Looking like your working through the process.
Don


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I finally got round to checking. there was a rust blemish in the cyclinder that i must have missed (tip - always check in natural light). I polished it out then rehoned the bores. Fortunately i have a selection of odd rings in a box, so chose the best fit ones. Put it all back together and now runs great. Interestingly the right exhaust is cooler than the left (hand over silencer), but it runs nicely now.


1968 T150/TR6R
1970 TR6
1970 TR6C

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