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just rebuilding my Engine, its in the car with its gearbox attached.

 

Thin belt conversion done, but foolishly didn't mark the front alloy pulley,  whats the safest way to find TDC in this instance please.

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Hi Pete,

 the simplest way is to insert a metal rod into #1 spark plug hole  - It needs to be held absolutely rock steady.

Usually an old spark plug body with the rod welded in place.

Rotate the crank and when it stops mark this position on the pulley.

Rotate the crank back the other way until it stops and mark this position.  TDC will be half way between these two marks.

If you have a degree wheel on the front of the crank that makes life easier still.

 

Roger

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16 minutes ago, RogerH said:

Hi Pete,

aren't our plugs 14mm !!!

The above is for 10 & 12mm

But it does describe what is needed

 

Roger

Yes you are right.  The principle is in the photo - just bore a hole through a spark plug to make your own.

This is the 14mm version

https://www.britbikes.co.uk/top-dead-centre-tdc-timing-tool---universal-598-p.asp

Here is a guide to the task.

https://www.wikihow.com/Find-Your-Engine%27s-Top-Dead-Center-(TDC)

Peter W

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I recently did this with my TR4A, using a piston stop. However the tough part was gently rotating the engine, as getting a good grip on the crank pulley or fan extension is elusive (I have a plastic fan, so using that was out). So here’s what I did.


1- disconnect the battery

2- pulled all the spark plugs and put the piston stop in the #1 cylinder (first take a peak in the open hole, or reference the dizzy, and make sure the #1 piston is not already at the top of the bore. You want the piston to travel a bit before contact, to remove any slop in the timing chain. I also removed the dizzy cap so I could watch the rotor as an indicator when approaching TDC on #1

3- chocked the wheels and released the handbrake

4- put the transmission in 4th gear

5- jacked up the left rear wheel so it can rotate freely (so I could rotate the tire and watch the dizzy rotor move)

6- then slowly/gently rotate the tire, while checking the rotor, until you feel the piston contact the stop. Put a mark on the crank pulley at the timing pointer. If you are unsure about the position, do not back it off a little and try again. Otherwise slop in the timing chain can throw off your result (see #1). Back it way off and try again

7- rotate the tire in the opposite direction until you feel the piston stop, and mark that spot.

8- repeat 6 & 7 several times and verify the marks match up

9- Mark half the distance between the two marks, and that should be TDC, (well close enough). 

10- be sure to remove the piston stop before reconnecting the battery!

Cheers,

Jim

 

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Pete

I made up a TDC lever using an old spark plug. I tension the external part of lever upwards with an elastic band and as the lever has about a 5:1 ratio it is simple to determine TDC. The off the shelf tools are great for central plugs but you have to careful when using them when the spark plug is inclined as they can jam.

regards

Rog

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