TDC Tool on Ebay

Hi All , I just took delivery of one of these http://www.ebay.com.au/itm/121987993030 , as nice as it looks in Ebay it's even nicer in the hand, really well made, and it works great in a Commando engine, probably better that a Duke as the plug hole is more upright.

Graeme

Guess that would be nice to have if you do a lot of engine work.
For me, a pencil or chopstick works well enough.
:mrgreen:

Well you will need to be really careful because of the angled plug hole. If the piston comes up and the plunger gets cocked it will get bent. Also any dial measurements (if you use it for that and not just finding TDC) will be off because of the angle. I guess you can do the geometry and figure out the real measurement. This is stated in the auction. If it catches on a chunk of carbon on top of the piston it could get stuck and bend.

The most accurate way to find TDC is to use a piston stop tool. At TDC you will see that the crank can turn 1-2 degrees each way but the dial indicator will not move much. With the stop tool you can get a much more accurate reading because you are measuring at a spot where the piston moves a lot for each degree of crank rotation. Sorry, there is a better and longer explanation for this elsewhere on the forum.

Russ

I have a similar tool since many years, works well, you have to take care not to bend the pin indeed when the spak plug hole is angled. Alternatively, a piston stop fabricated from an old spark plug is also an accurate tool for determination of the TDC.

Yes, the piston stop and degree wheel is accurate where as the dial indicator will register nil a few degrees along the TDC plane.
3 degrees BTDC and 3 degrees ATDC is more than a full step adjustment on the cam. Just sayin.
The other issue to mention is be sure to be on the stroke where the valves will not interfere.

a piston stop and a degree disc is the only way to be accurate imho ,,,,,,,,,,,,,baz

baz said:

a piston stop and a degree disc is the only way to be accurate imho ,,,,,,,,,,,,,baz

Click to expand...

Agreed, The dial indicator will just get you in the area.
They work great for setting advance on a two stroke however. Jim

I take it you use a piston stop thusly; Rotate the crank until the piston hits the stop, note the reading on the wheel, rotate in the opposite direction, note the reading and split the difference for TDC?

To find TDC, I have an old spark plug with the electrode pulled out, and use the soap bubble technique.

Danno said:

I take it you use a piston stop thusly; Rotate the crank until the piston hits the stop, note the reading on the wheel, rotate in the opposite direction, note the reading and split the difference for TDC?

Click to expand...

Correct.

Danno said:

I take it you use a piston stop thusly; Rotate the crank until the piston hits the stop, note the reading on the wheel, rotate in the opposite direction, note the reading and split the difference for TDC?

Click to expand...

That is the accurate way to do it. Just be careful because the piston stop stem will be in the way of the valve and will bend the valve if it tries to open.

I install the piston stop with the piston 90 degrees after TDC on the compression stroke and then rotate the crank backwards until the piston is against the stop and make a mark.
Then I remove the piston stop and turn the motor to around 90 degrees before TDC on the compression stroke and then re-install the stop. Then rotate the crank forward to the stop and mark it. That way I do not have to rotate the motor through a valve cycle. Jim

comnoz said:

Danno said:

I take it you use a piston stop thusly; Rotate the crank until the piston hits the stop, note the reading on the wheel, rotate in the opposite direction, note the reading and split the difference for TDC?

Click to expand...

That is the accurate way to do it. Just be careful because the piston stop stem will be in the way of the valve and will bend the valve if it tries to open.

I install the piston stop with the piston 90 degrees after TDC on the compression stroke and then rotate the crank backwards until the piston is against the stop and make a mark.
Then I remove the piston stop and turn the motor to around 90 degrees before TDC on the compression stroke and then re-install the stop. Then rotate the crank forward to the stop and mark it. That way I do not have to rotate the motor through a valve cycle. Jim

Click to expand...

Thanks. Makes sense when you can see the open valves though a spark plug hole.

Using a pencil or similar is really clever as some people have been known to find out to their cost when a bit breaks off in the combustion chamber......
I was taught to use a steel tool that stopped the piston just before reaching TDC .......note the degree reading on the degree plate fitted to the crank.....turn the motor back till the piston again stops as it makes contact with the tool ...note the reading on the degree plate and halfway between the two readings is exactly TDC. Very simple and accurate when you have a motor on the bench with no primary chain case etc fitted. To double check you set the stop tool in a different position.... Attached to the alloy plaie was a plastic degree plate that was moveable. Last time I saw a PILE of them in Birmingham they could be bought for £1 or so each and I laught when I see the prices now asked for them on E Bay. Oh look the new one in my hand is marked W.E. WASSELL (B'HAM) LTD which shows its age..... and mine.
The degree plates were alloy made from the lumps left over after chomping out from plate alloy the 'cooling muffs' fitted to Manx /G50 / 7R front brakes and customers road going bike brakes back in the 60s wnen such things were the latest fashion accessories / go faster goodies! Yes I even had one on my olde bolt up two piece Dommy front hub (heavy but they worked well)but I was very young at the time. PLUS it was correctly shrunk on......
Ever see Mr Jack Williams brake test results done in the early 50s whilst at AJS developing the 7R and E95 motors comparing the different methods of inserting the cast iron liners in alloy hubs? Screwed in, bolted in, shrunk in , cast in.......The differences to braking each method gave were rather significant. NO I did not note them down for future use when I had the book in my hands for a few days but I did note down his remarks on high linear speed primary chain efficiency (or to be accurate.. inefficiency). Do people still use 98% for motor cycle primary drive chain efficiency?

comnoz said:

baz said:

a piston stop and a degree disc is the only way to be accurate imho ,,,,,,,,,,,,,baz

Click to expand...

Agreed, The dial indicator will just get you in the area.
They work great for setting advance on a two stroke however. Jim

Click to expand...

Yep, I sold my 35 YO timing dial indicator on Ebay awhile back and much to my surprise got $75 for it...bought it waaay back in the '70's to time RD350's.

If you want, get the Motion Pro degree wheel Part # 08-0092, its 15 bucks.