classic motorcycle forum
Motorcycle Discussions => British Bikes => Topic started by: Petergj on June 27, 2017, 11:07:41 AM
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Help needed
.. I have a 1969 Triumph T100R in a Rickman frame with a single Amal 626 carb and 2 into 1 exhaust. The engine has just been re-bored to 0.020 oversize after the previous owner scuffed the pistons/bores. The engine runs well and starts very easily with the ignition timing set with a strobe, but the engine runs very hot. To ensure the carburation is OK (currently running with 190 main jet), I am about to replace the carb with a new one to be sure there are no air leaks between the throttle slide and body. I will also remove the slip on style silencer to see if that is increasing exhaust restriction (and retaining heat in the engine). Beyond that, I have run out of ideas!
Has anyone else experienced similar over heating issues and what was the solution? Any comments welcomed.
Thanks,
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"Hot" is a relative term though. Last week was extremely hot (in the UK) so when did you try it? A very hot engine is usually a weak mixture, wrong timing, "tight" engine, inefficient oil pump, valve timing out, leaking head gasket, tight tappets, binding brakes, soft tyres, etc etc or mixtures and parts of all of it.
If the carb is the same as when it ran OK before (you have had it running OK I take it?) then that can be discounted (provided the flange isn't badly leaking) but you need to check everything you've done.
Is it down on power too?
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I would suspect a new rebore pistons and rings.The motor will run hotter until the new bits wear in.If you are really worried ,lift the barrels and see whats going on.Otherwise try a bit more ignition advance.
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Thanks for your comments - I have had the bike for about a year (knowing the bores were scuffed when I bought it) and it has always run hot, hence the drastic change to replace the carb and ensure there are no leaks in the carb around the throttle slide. There is a thick heat isolator between the carb and head. All frame parts are OK (wheel bearings, brakes, etc). No lack or power and healthy return of lubricating oil to the frame (I know that is not a good indicator of adequate bottom end lubrication). I will re-check the valve timing but I am sure that was done when the re-bored barrel was fitted. Failing these checks, it looks like a full tear down.
Does anyone know if these engines are sensitive to exhaust back pressure?
Regards,
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Hi,
Does anyone know if these engines are sensitive to exhaust back pressure?
Short answer, no
I would remove the timing cover and check the crank oil feed seal
While its off check the valve timing
Whats the heat insulator made of? is it a soft material?
Soft insulators warp the carb flange !!! the insulators need to be made of "Tufnol" (paxolin)
Check the fuel height in the carb.
What was piston to bore clearance set at when the rebore was done?
Were the piston ring gaps checked at the same time ?
John
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There is the genuine "thick" paxolin gasket between the carb and cylinder head.
Looks like pulling the timing cover will be time well spent.
The engine has a Pazon ignition system with the timing set at 38 degrees (as per recommendations). Is it worthwhile advancing (or retarding) the timing to see if the heat generation can be reduced (there is one comment in the thread to advance the timing which I will try).
In terms of dimensional checks, the engine was rebuilt by a reputable bike restorer so I am not aware of any piston-bore and ring gap dimensions.
Appreciate the comments in the replies.
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Paxolin and Tufnol are very different materials, and I should imagine you have a Tufnol item fitted.
Anyway, you really don't want to start fannying around with settings to see if it improves. If it's at 38' then it's correct so leave it and look elsewhere.
I'm still confused though....has this bike ever run right in your ownership?
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Rex, the engine was running hot when I got the bike and breathing heavily. The barrels were bored out and oversize pistons/rings fitted but the bottom end was not dis-assembled (may be a mistake with hindsight) but the condition of the crankshaft/bearings were reviewed and nothing deemed abnormal without removing the crankshaft.
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So have you ascertained that the bike actually is running hot, and how was it done? Have you compared with a similar bike? Sometimes rocker box oil leaks give this impression as it stinks of hot oil when the oil runs down over the head and it gives off little wisps of smoke, too.
Needing a rebore is not in itself a reason for running hot.
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Hi,
Have you checked the timing with a strobe?
Also verify that the timing marks are correct (or not?)
The timing marks are not always 100% reliable
Are the correct heat range plugs fitted?
John
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The plugs are Champion N4C (when I acquired the bike, it was fitted with NGK B7ES plugs).
The timing has been set with a strobe and the timing mark checked using the slot in the flywheel accessed through the inspection plug behind the cylinder barrel.
Th engine is running Morris 20w50 oil and I will change this to Morris SAE40 at the next oil change.
The re-bore was completed due to the scuffing of the bores - I only think it is running hot based on comments from the guy who rebuilt the engine following the re-bore saying it may scuff again if I was not careful and the right hand cover feels hot (as opposed to warm). Maybe this is the way they all are and I am unduly worrying? Any drip of oil from the rocker box does quickly burn off with a "wisp" of smoke.
Thanks for your comments.
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Sounds like the bloke who rebuilt the engine was giving you some advice about oils or running in rather than dire warnings about the engine condition. Is there no-one locally you could ask about how hot the engine is?
Being air-cooled there are big variations in ambient temps....Death Valley to Alaska in winter,and the engine's are pretty tolerant of heat all things considered. How hot is the oil tank side after a fast run? Pleasantly hot or unpleasant to touch?
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I would expect the timing cover to get hot enough to make it uncomfortable to touch but not to burn your hand.
As Rex says, check the oil tank temperature - you should be able to hold your hand on it for a couple of seconds even after a hard run.
I have a digital laser thermometer gadget (like this: http://www.maplin.co.uk/p/infrared-thermometer-with-laser-targeting-n92fx but mine was cheaper) that I find very useful in a variety of situations.
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Thanks again for all your comments. As planned, I changed the Amal carb for a new Amal 626 Premier this weekend and fitted with a Burden wire gauge air filter (as fitted to the original old carb). This was set up to the original T100R spec by Burden and as a result the engine is running well with a 180 jet compared to the 190 main jet I was running with the old carb (the old carb was fitted with a new 190 jet and needle/jet as part of my investigation). A plug check showed the mixture was OK (light brown colour) with the Premier carb.
Would anyone recommend running slightly richer to avoid any chance of running weak?
lansoady, the timing cover is hot and just shy of burning my hand. The oil is returned to the frame as a reservoir and the oil returned to the frame is warm and not hot. I have a digital thermometer with a probe which I will use tomorrow and get an idea of the timing case temperature (I may buy the laser thermometer you suggest when cash is available!).
Right now I am planning to double check the timing with a strobe and carefully continue to run the engine in.
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That doesn't sound excessively hot to me.
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As a quick update, I fitted a new Amal carb from Burlen including 4 Cutaway Slide Hard Anodised, 180 Main Jet, 106 Needle jet and Size 17 Premier Pilot Jet. I ran the bike last week end and the plugs were a very light brown - see pictures. I plan to drop the circlip to richen up the mixture and get a darker plug colour.
The engine still seems to be running hot but I do appreciate other comments which suggest the engine is not running but the right hand pipe of the 2 into 1 is well blue! I did try to measure the head and timing cover temperatures with a touch thermometer but the test was inconclusive - I'll have to invest in the optical device from Maplin as suggested.
Does anyone think the coil could be causing some of the issues? The coil is a single unit with two HT leads made by EMGO. Would it be worthwhile changing the coil for another unit?
Again, any comments appreciated - I am planning to take the bike to France for a rally in two weeks and will cover approximately 100 miles. Time is running out to fix the "overheat" issue if there is really one. I will cover 30-40 gentle miles before going to France.
Thanks for all your comments.
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The engine still seems to be running hot but I do appreciate other comments which suggest the engine is not running but the right hand pipe of the 2 into 1 is well blue!
If one pipe only is turning blue, it suggests your engine is not running equally well on both cylinders.
Put a dab of oil on each pipe up near the exhaust ports, and when you start it from cold, watch which side boils the oil into smoke first. They should go together. Waving your hand near the pipes can also detect if there is a temp difference between them on startup - but is usually a good recipe for getting burnt fingers. !
If one cylinder is only running poorly, your engine could well be getting too hot as one cylinder labours to do all the work. This really needs to be sorted before heading off anywhere, or to a rally.
Can you switch the coil around, so it fires the cylinders opposite to how it is now ?
If the problem switches sides, you know there is a problem on the electrical side of things.
I missed the start of this, are your point(s) correctly set, and correctly timed.
And the ignition advance side of things correctly advancing and retarding ?
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R, the ignition timing is Pazon and the advance retard works - timing set using a strobe.
I have seen other threads about the exhaust on Triumphs differing in colour - the right hand exhaust pipe getting more blue. I do wonder if the blue is due to the 2 into 1 design and greater flow of hot gases in this area.
I will let you know what happens when the needle is raised and if I can switch the HT leads.
I does not appear that one cylinder is getting hotter than the other - maybe the heat is a consequence of the recent rebore as others have pointed out.
Thanks for your comments.
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Rex, I measured the engine temperatures after a run using a touch digital thermometer and got 55 Deg C on the timing cover at the pressure connection point and 135 Deg C at the third fin from the top on the cylinder head.
I noted the Amal Premier I received from Burlen was fitted with a #4 throttle slide and when running port throttle the plugs are a greyish colour after a plug chop - running lean? Would a move to a #2 or #2.5 throttle slide be too much of a change to richen up the mixture when running at part throttle?
Appreciate any comments.
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Those temperatures sound fine to me.
4 to 2.5 would be too big a jump IMO. Plug chops at part throttle are not very accurate. Unless it's got a flat spot just off tickover I'd leave the slide alone.
TBH I think you're worrying about nothing.
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The temps should be comparative as they don't mean much in themselves.
Is the slide not as specified in the manual?
It's a common enough bike and you shouldn't have to do plug chops.
(Incidentally, I don't know if it's correct or not, but some American tuning bloke posted a while back somewhere else that plug chops are only vague at best on ethanol fuel. Can't rely on them anymore it seems}