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T140 TS low compression
#783776 09/08/19 3:28 pm
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I finally got the T140 running, but with a top speed of only 80 mph, so the first step was a compression check. The drive side cylinder was about 110 psi with 60 psi on the timing side. Next a quick check with a few cc's of oil in the TS cylinder gave 100 psi indicating a ring problem. After removing the cylinder barrel the only difference I noticed was a scuff mark on the TS piston,

[Linked Image]

At this point I will do a cylinder hone with new rings, but I have some concern about this mark.

Does this mark tell me anything about why the compression was low?

The mark feels smooth and both cylinders look good, so is it safe to use the same pistons?

Attached Files IMG_0034.JPG

Craig Zaspel

T100R
BSA A10
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Re: T140 TS low compression
Dr. Z #783777 09/08/19 3:43 pm
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Check that the rings aren’t sticky in their grooves.


Amateur Loctite enthusiast.
Re: T140 TS low compression
Dr. Z #783828 09/09/19 2:55 am
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Also what exhaust are you using...…...I can remember having a Trident with pattern Campbells mufflers that wouldn't do over 80....replaced with more open sports type mufflers and the same bike did over 110 mph easily [maybe could have got more, but didn't try]. Plus just felt more powerful all round.

If your bores measure up OK, using that piston again [with new rings] would be fine.

Last edited by tridentt150v; 09/09/19 2:55 am.
Re: T140 TS low compression
triton thrasher #783832 09/09/19 4:14 am
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Thanks TT I will check that with the new rings.

Tridentt150v: I have short reverse cones with baffles on 2 inch exhaust pipes. The bores measured up OK at 40 over.

Thanks for the replies.


Craig Zaspel

T100R
BSA A10
Re: T140 TS low compression
Dr. Z #783833 09/09/19 5:58 am
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I had Unity short reverse cones that were restrictive.

The simple test is to try the bike with no silencers.


Amateur Loctite enthusiast.
Re: T140 TS low compression
Dr. Z #783842 09/09/19 11:37 am
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Agreed re trying without silencers. I had Campbells megaphone shaped silencers on a T140 I bought once. Utterly gutless and would not go over 80. I took them off and it was as if it was supercharged, in comparison.


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Re: T140 TS low compression
Dr. Z #783852 09/09/19 3:41 pm
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I don't think the mufflers are the problem when has 60 psi compression in one cylinder.


1978 Bonneville T140E
1974 Trident
1970 BSA Thunderbolt
1971 Norton Commando
1972 Norton Commando
1973 Norton Commando
1974 Norton Commando
2018 Kawasaki Z900RS


Everything will be alright in the end. If its not alright, its not the end.
Re: T140 TS low compression
Dr. Z #783954 09/11/19 2:53 am
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I will post the results when I get new rings, with and without silencers.


Craig Zaspel

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Re: T140 TS low compression
Dr. Z #783969 09/11/19 10:39 am
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Flip the head over and pour the CHamber full of lacquer thinner and see if it ends up in the ports, If so you also have a valve issue! I have seen lots that the piston scuffed like that and the comp wasnt much if any lower, I bet you have a valve issue. Prob some trash between the valve and seat. Good luck

Re: T140 TS low compression
Dr. Z #783970 09/11/19 10:48 am
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Not sure if these were new rings or original, but if rings don't do the job of taking heat out of the piston, and transferring it to the cylinder wall you will get piston pick up.

What does the gudgeon/wrist pin look like? Any colouring on it?

I probably wouldn't worry about that scuff, but that's just me.


'51 C11 in a '54 C10L frame. Back on the road...
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Re: T140 TS low compression
Dr. Z #784001 09/11/19 7:54 pm
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JakeH, thinner stays in place with no sign of a leak.

Gringe, The pistons are 0.040 over, but I have no idea when it was rebored. Also the wrist pins look OK, and I will not worry about the scuff.

My long term plan for this is to make a 76 degree engine as a retirement project if I can retire. As Kent Shaun would say, "that is a big IF"


Craig Zaspel

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Re: T140 TS low compression
Dr. Z #785160 09/23/19 2:33 am
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New rings solved the compression problem. I have in the meantime noticed that the carbs only open to 3/4 instead of full throttle, so that is the next thing to work on. I have not yet tried TT's suggestion to run without silencers.


Craig Zaspel

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Re: T140 TS low compression
Dr. Z #785174 09/23/19 7:51 am
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If you take the silencers off wouldn't you have to increase the length of the pipes?

Dave

Re: T140 TS low compression
Dr. Z #785177 09/23/19 9:31 am
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Originally Posted by Dr. Z
New rings solved the compression problem. I have in the meantime noticed that the carbs only open to 3/4 instead of full throttle, so that is the next thing to work on. I have not yet tried TT's suggestion to run without silencers.


If the throttles don’t open, that will slow you down.


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Re: T140 TS low compression
dave jones #785178 09/23/19 9:34 am
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Originally Posted by dave jones
If you take the silencers off wouldn't you have to increase the length of the pipes?

Dave


I don’t think it matters. They don’t have very scientific exhaust systems.


Amateur Loctite enthusiast.
Re: T140 TS low compression
Dr. Z #785202 09/23/19 2:53 pm
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I still don't get what taking the silencers off will prove. His problem was low compression which he has obviously solved. Ride it and enjoy it.


1978 Bonneville T140E
1974 Trident
1970 BSA Thunderbolt
1971 Norton Commando
1972 Norton Commando
1973 Norton Commando
1974 Norton Commando
2018 Kawasaki Z900RS


Everything will be alright in the end. If its not alright, its not the end.
Re: T140 TS low compression
htown #785210 09/23/19 3:51 pm
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Originally Posted by htown
I still don't get what taking the silencers off will prove. His problem was low compression which he has obviously solved. Ride it and enjoy it.


It will prove very noisy.


Amateur Loctite enthusiast.
Re: T140 TS low compression
Dr. Z #785224 09/23/19 5:55 pm
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It is fast and loud enough with silencers; moreover, my wife and neighbors would not like me running without silencers


Craig Zaspel

T100R
BSA A10

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