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Timing Marks don't line up with TDC?

11K views 13 replies 8 participants last post by  shootist2004 
#1 · (Edited)
Hello All

Any help with this would be much appreciated...

After replacing piston rings and re-building the top end I thought I better have a look at the timing.

Checking the top dead centre (TDC) of piston 1 (right hand facing the front) I find that the timing pointer on the primary side is not lined up with the TDC mark when the piston is at the top of its travel. See photo 1 below.

It's slightly to the right of the marks.

When I line up the pointer with the marks the piston is lower as shown in photo2.

Can anybody shed light on why this should be and what I do about it?

Many thanks

JP
 

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#2 · (Edited)
That isn't tdc

The mark should be 38°

It still doesn't look right but if your bike has a bolt behind the cylinders it may have a slot that indicates 38° on the crank. It depends on the year. Did it run ok ? Did you move the timing pinions?

Edit- if it's a t140v it should have two slots tdc and btdc
 
#3 ·
As Dave mentions the timing mark should be 38 degrees, I had a similar problem on mine, the pointer was slightly off from the mark, upon inspection I found that the primary case had been repaired by a PO but the pointer was not put back in the correct position, as verified by using a dial gauge, and when I bought a new outer cover.
 
#4 ·
You need to check both tdc and 38 btdc with the crank slots using the access bolt behind the cylinders. Outer part of rotor with timing marks can come loose and may have rotated on the inner hub. I have one out in the garage that you can turn about a 1/4 in either direction.
Here's how you confirm the timing marks as the outer part of the rotor can come loose on the inner. Triumph flywheels have two notches in them, one at TDC and on at 38 degrees before TDC (full advance). On the top of the case behind the cylinders there is bolt. Remove the bolt and use a tool like this to drop into the slots. http://www.ebay.com/itm/Timing-Tool-...cb57fa&vxp=mtr. You could use an allen wrench if you are careful.
Put the bike on the centerstand and pull the plugs. Remove the little plug in the primary cover at the end the crank. Put it in fourth gear and use the rear wheel to turn over the engine. Turn the engine until the pistons are at top dead center. I use a plastic straw as a guide. The timing tool should now drop in the tdc slot but you might have to slightly turn the wheel a little one way or the other. Remove the tool and now turn the wheel backward and look in the primary cover opening until the pointer lines up with the notch in raised pad on the rotor and then the tool should drop into that notch.
 
#5 ·
Hi JP, When I was having problems with timing I marked my rotor for tdc. I have an earlier bike with lower timing pointer, but on my rotor tdc will line up with the with the right hand leg of the "U" in Lucas word on rotor. On my rotor 1deg is .024" which would put tdc about 7/8" clock wise from the 38d line.

So on your bike with top left timing pointer from the 38b line when you go to tdc the outer rim of rotor should move about 7/8" rotating motor in normal direction.

I don't know what the mark off the pad is. Looks like about 35b to me.?? From your pencil marks the rotor position looks plausible.

You can simulate timing tool of sorts by removing plug behind cyl. Get a 1/4" dowel, drill bit or something. About 3-4" long. Tape up the end & make it fat so you can't loose it in motor. Turn eng real slow as the slot passes by quickly. Stick the dowel into the timing slot on flywheel. Center the dowel/slot in the hole in case. The slot is precisely machined so the tool fits into flywheel slot without play. There is a slot at 38b & tdc. With a good flashlight & mirror you can see slot also. You'll see what I mean if you try this & you'll compare tdc slot with your pencil mark, then do 38b & you'll know what you have.

This will allow you to move forward, but it's handy to have the real tool for when you need it. They are not costly.
Don
 
#6 ·
Thanks everyone for good advice.

The reason I was trying to locate TDC with the piston height was that the plug behind the cylinder is seized in and rounded off by a previous owner. I doubt it has been removed in about 40 years. So although I do have one of those tools for finding the 2 flywheel slots I can't get access.

[Someone suggested blow-torch heating the case around the plug to loosen it but I haven't tried this yet… sounds tricky]

I do understand that the strobing / timing setting should be done at 38d BTDC and not TDC. My issue is finding these positions without the plug/location-slot method i.e.

1. Is finding the highest point of travel of the piston = TDC (or is this not a legitimate way of finding it)?

If not then that could explain why the pointer is not pointing at the marks. i.e. the highest piston travel does not = TDC (is this what you meant Dave?)

If it IS a legitimate method and the timing pointer is then not pointing at any of the factory stamped marks, then why not?

Potential answers: pointer moved somehow (tribsa) or the potential for the marks to move as the rotor can move position if loose as htown16 said.

[My concern was that it was something I had done wrong in replacing the cylinder head, although I can't think how this would affect it… please correct me if I'm wrong]

If the outer rotor (with the factory marks on it) HAS moved :

2. How do I move it back and tighten it or should I not worry about it and just scratch/paint my own TDC and 38d BTDC marks on it as suggested by Don?

Thanks again

JP
 
#7 · (Edited)
Rather than a torch I would use a paint stripping hot air gun. Mine is a ryobi 2.5kw?
Add some plus gas as well and possibly several heAt cycles. That is a big lump to heat You may be able to hammer a slightly too small metric onto it and replace the plug
There are two thread types, buy the correct one

Do you have any evidence that the pointer/ mark is wrong?
It should be held on with a woodruff key so should not be wrong
 
#8 ·
TDC is TDC, when the piston is at its highest point.
That can not be doubted.
You need to get the bolt behind the barrels out, somehow.
If the head is rounded off beyond repair, you could cut a slot in it and use a wide screwdriver, a little heat will help.
Maybe an impact driver if its stubborn.
 
#9 ·
Thanks both.

Dave, the pointer looks good and solid and I doubt it is the problem.

Caulky, ok thanks. I'll try all the methods suggested to get the plug off but If I can gauge TDC pretty accurately by the maximum piston height (in gear using the back-wheel as a gentle hammer to move the piston fractionally up and down) do I really need to?

If using a stick in the spark plug hole is too crude a method then I seem to remember there's a gauge you can insert to measure piston movement. Anyone do it like that or is the plug/flywheel slot method the only way to go?

Whichever method I use in the end and I still find that TDC doesn't point to any of the factory marks, is this a problem? i.e. do I need to adjust the rotor or should I just go ahead and make my own marks to strobe at 38d?

Cheers

JP
 
#10 ·
Forget the tdc. It is of no use other than to calculate the 38° point.

The factory put those slots in the crank so that you can confirm the rotor mark.
I was referring to the rotor mark rTher than the pointer- I thought that you were suggesting that the factory mark had somehow slipped around?

You need to use a strobe to time and for that you need to use the slot (only because you have somehow cause to doubt the precision of the pointer/rotor mark) and once you have faith in the marks, time according to the instructions at roughly 5k rpm

Yes you can measure down but it is far harder .just get the plug out
 
#11 ·
I'm not intimately familiar with the T140, but I assume it's like all the other Triumphs and that mark is on the rotor? The rotor is keyed to the crankshaft, but two things can happen: the key can sheer, or the rotor detaches from it's inner hub. In both cases the rotor body can rotate relative to the crankshaft until it jams in position. If you're running points the relative position of the rotor to the crankshaft makes no difference to the electrical system and you wouldn't notice it in terms of the engine working.

I'll add that if you don't want to go down the rabbit hole of pulling the rotor to check, I would just remark it. And I would check it again later to see if it slipped any.
 
#12 ·
Other than the op's assertion that because the piston is at TDC and the (38°) rotor mark does not line up, there is no evidence whatsoever that anything is wrong.

He is measuring two different marks and because they don't line up, says something is at fault.
The rotor mark does not indicate TDC
 
#13 ·
Hi Htown, Ok, I see your dilemma. I would be most careful in the timing plug removal. Basically don't do it. If you must, prepare to do a thread repair. That leaves you at great risk. You can approximate 38d with piston travel. That will get you quite close. Study the old manuals for that info.

Your only real choice to be sure is pull timing cover & use a degree wheel. You can find tdc by putting a tight fitting dowel in plug hole & jamb the piston gently against it. Mark rotor, (& degree wheel) then turn eng around other way & jamb piston again. Make 2nd mark. Now split the marks with dividers & mark rotor gently with very sharp center punch. Mark degree wheel & split degrees on degree wheel. I've used degree wheels dozens of times & very easy with some practice.

However in your case I would do nothing if bike was running good prior. I would be very careful about heating case or bolt with a torch. Even then it may not come without thread damage. You could repair threads in place, but it would most certainly put a few chips in the sump which would be hard to flush out.

I've not tried this, but if you can feel bdc with a bent wire or the like the U on lucas as I said earlier will line up with your timing mark since it's 180d from my timing mark. Part #s for our rotors are the same.
Don
 
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