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#303024 03/14/10 11:36 am
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kellyt Offline OP
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Hi guys,
What's the compression pressure figures for my 1960 Triumph 3ta?
It is running uneven and I would like to check the compression before removing the head to fix an oil leak.

Thanks, Kelvin


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Hi Kelly -

What are the readings you're currently getting? Hot? Cold?

At the risk of insulting your intelligence, be sure to have WOT when checking...

Afterthought: In my mind, 'running uneven' encompasses ALOT of territory...a bit more description of symptoms? (besides leaking oil...they ALL do that! grin )


Steve

Last edited by JubeePrince; 03/14/10 5:16 pm. Reason: afterthought

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kellyt Offline OP
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Hi Steve,

The reading hot with WOT is T/S 102 psi, D/S 104 psi.
Cold with WOT is T/S 100 psi, D/S 100 psi.

The uneven running is rather lumpy on low revs espicially when on over run at say 30 mph, it also spits back through the carb at times even when hot and when you open the throttle from tickover - like pulling away.

I am using the stock carb although I have a brand new carb I have tried and it is still the same (spitting back wise) and there are no air leaks because I have checked this several times.

The timing is spot on and new plugs fitted, I have had this problem for a quite a while and now I would like to get sorted before I take her to France in May.

I read somewhere that this spitting back through the carb can be caused by a problem with the cylinder head but I can't remember what it was or where I read it.


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Kelly -

So....when I use the word 'lumpy', I think of a rich condition, 8-stroking and black fluffy soot on the plugs...

Spitting back through the carb can indicate a lean condition....or poor ignition/timing.

If carb has been swapped and no change in running, then perhaps it's not fuel related...If not fuel then what? Ignition. Interestingly enough, I came across one of your threads from 2008:

https://www.britbike.com/forums/ubbt...l+fault%3F%22&Search=true#Post145424

You seem to be describing the same behavior that you were experiencing back in '08. Did you definitively sort out the distributor and coils problems?

Steve


'77 T140J Silver Jubilee
'82 T140LE TMA Royal
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kellyt Offline OP
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Steve,

Yes,the problem I had back then was cured by installing a modern twin output coil which has been fine since, I had been talking to members of the vintage motorcycle club and this is what they have on their 5ta's & 3ta's when they got the same problem.

I think it is a mixture problem because the plugs are a lightish brown, I have now raised the needle one notch and tomorrow I will see if that has improved things.


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kellyt Offline OP
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What should the compression figures be?
I need to know if I should install new rings when I remove the head to fix the oil leak.


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Don't know the answer to that one Kelly, but I bet someone here will be able to help....100 sounds kind of low, but I'm not as familiar with the C range bikes....


Cheers,

Steve


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Hi kellyt, are you still running the distibutor? My ex-wife had a 3TA in the early 80's, and it displayed similar symptoms. After converting to points (new exh cam, AAU, 6CA points plate, and timing cover fitted)it ran perfectly. The old distributor had some slop in it, it didn't seem excessive to me at the time, but it obviously was.

Just a thought.
Regards,
SR

PS: I changed the carb a little later, which also made a difference. I used a 27mm Concentric 626 from a Trident (fitted an idle screw to it of course) which you would believe was way too big, but it worked really well, great mileage and it would plonk like a trials bike. Strange.

Last edited by Stein Roger; 03/14/10 10:08 pm. Reason: PS...
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kellyt Offline OP
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Hi SR,

The distributor is not being used with the twin output coil but the points in it are being used to fire both cylinders and it works a treat.

Cheers, Kelvin



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Kelly, I prefer doing a leakdown test instead of a compression test. Compression testers, for some reason can be misleading. One tester will tell you you have say 110 LBs and the next one will say 145. That is why many mechanics say "just so the cylinders are within 5 or so percent of the same".
A compression test will tell you what you need to know if you take readings (with the same tester) throughout the life of the engine. That way you have a known baseline.

If you aren't familiar with leakdown testing, it is done by charging the cylinder with compressed air and measuring how much is lost. It is easy to pinpoint a problem to valves, rings or head gasket, by listening for the source of the leak.
Just my .02



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kellyt Offline OP
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Thanks Steve,

I will try the leakdown test but in the meantime I have squirted oil into the bores, tested again, and the compression on both cylinders has risen by 20 psi, I suppose this is telling me that the rings needs replacing.


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kellyt Offline OP
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Leakdown test carried out and no leaks found.


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You say you are not using your dizzy but you are...
You are still using the points, cam and drive shaft.

As you cannot really tell by just looking at your cam and your ignition will also be sensitive to any drive shaft bearing wear, I would get the dizzy serviced.

There is a company in Cambridgeshire called Roy Price Productions which provides this service.
He can be contacted on:01480 473225

At this point I would not worry about the compression figures as your engine is at a very low tune state and only pushed 18bhp when new.

I am assuming you have the original 375 carb... they run great on these and should you have any wear then I would get it rebored, sleeved, refaced and serviced (usually about £45) rather than replaced by a Concentric. I use Alverstoke Restorations for this in Gosport (02392 580708).
He provides a worldwide service.

I think your engine is pre-crank stop, so to set the timing acurately you will need to mount a timing disk on the end of the crank and set up a pointer when the dizzy comes back.

The Pazon should not make much difference to your timing but you owing to the removal of the rotor arm ect, you may need to retard your ignition by a smidge. But with a serviced dizzy, go back to standard points gap.

Regards

CG.


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Try checking the ignition timing on both sides, use an inductive strobe light with the pickup on the "king" lead and fire at the timing mark just to check that they are concurrent (no flickeI set the timing on my 3TA at 37 BTDC @ over 4000 rpm. A retarded ignition timing gives a good idle but tends to spit back when you open the throttle, as does tight-ish inlet valve clearance, I set mine at 1/3 turn open from the back of the cam rather than the 1/4 turn recommended.

Last edited by andrewinpopayan; 03/18/10 12:17 am.

99% of carb problems are electrical.

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kellyt Offline OP
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Thanks CG & Andrew,

I had the dizzy serviced by Roy Price a while back so I don't think the problem lies there,I recently am get a lot of popping from the exhaust when easing off on the throttle but only when moving and it seems to be getting worse, while trying to fix this I am getting a lot of spit back when I open the throttle (which the bike has always done but not much)

I will try what you suggest Andrew.


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A 3TA is usually dead smooth because it is so mildly tuned. Spitting back, as has been mentioned before, is usually over advanced timing or a weak mixture but can be bad plugs too. Does it spit back at all throttle openings? It does actually sound like you have bad timing or tappets or a weak mixture at low throttle openings. Banging in the exhaust when slowing down is a weak mixture alone or a rich mixture along with an air leak in the exhaust. If you have no terrible air leaks in the manifold or exhaust (seal the exhaust with silicone sealant at head and silencers) and the timing is correct (take up all the backlash in the dizzy when setting)then try changing the pilot mixture. If that doesn't work try a slide with a smaller cutaway to richen it although it is very unusual to need to do this. . If your inlet guides were very worn you may get a weak mixture that way but also smoke when slowing down that clears when you pull away. These parts would have to be really terrible to make a difference. Tappets are set at .010" on these bikes, I think.
dave

Last edited by dave jones; 03/18/10 9:35 am.
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kellyt Offline OP
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I have removed the head to fix the oil leak and I have found that the valve guides are worn well beyond their service limit as are the piston rings, looks im on the right track now!


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