Checking TDC with front pully markings.

[dw350i]

Is there an easy way of confirming that the pully marks are correct for TDC?

[adam quantrill]

The recognised way is to use a dial gauge on the No. 1 piston. You need to remove the spark plug and poke something (a rod) down the hole (oooh err missus). Attach the gauge to the rod and it should top out at TDC.

Failing that, use a plastic straw and a ruler. It will show up any gross errors.

BTW an easy way to rotate the engine is to stick it in 4th, jack up one rear wheel and rotate that.

Edited by adam quantrill on Tuesday 3rd October 08:31

[toltec]

One trick I was told about, not tried it myself though, was to form a soap bubble across No.1 spark plug hole and watch the size change to find TDC.

[Boosted LS1]

toltec said:

One trick I was told about, not tried it myself though, was to form a soap bubble across No.1 spark plug hole and watch the size change to find TDC.

That sounds quite novel but you'd be better using the balloon on a tube method. It's deadly accurate.

I just put something stiff but soft in the plug hole, small plastic tube and watch it rise to tdc whilst I rotate the crank using a long bar.

Boostewd

[dickymint]

Boosted LS1 said:

toltec said:

One trick I was told about, not tried it myself though, was to form a soap bubble across No.1 spark plug hole and watch the size change to find TDC.

I just put something stiff but soft in the plug hole.

Ouch!

[toltec]

dickymint said:

Boosted LS1 said:

toltec said:

One trick I was told about, not tried it myself though, was to form a soap bubble across No.1 spark plug hole and watch the size change to find TDC.

I just put something stiff but soft in the plug hole.

Ouch!

I'm impressed - theres no way I could even reach!

Tube and balloon would be more durable - use an old plug with the ceramic removed maybe. Hmm, coming to a Halfrauds near you soon...

[dickymint]

Would it not be dependant on a good piston ring seal?

[350zwelgje]

Check the correct TDC (there are two possibilities!), by having the rotor on the distributor point to cylinder number 1. Difficult when everything is removed, but this is one of my checks before I start to work on an engine.

Think that the non-balloon ways are ok to just quickly verify if the existing mark is in the right position.

Rob

[honourablepickle]

dial guage and a ball ended rod through a drilled out plug has always worked for me

[rev-erend]

Boosted LS1 said:

toltec said:

One trick I was told about, not tried it myself though, was to form a soap bubble across No.1 spark plug hole and watch the size change to find TDC.

That sounds quite novel but you'd be better using the balloon on a tube method. It's deadly accurate.

I just put something stiff but soft in the plug hole, small plastic tube and watch it rise to tdc whilst I rotate the crank using a long bar.

Boostewd

So is TDC when the piston first reaches the top - as I guess it seems to stay there for say 5 ~ 10 degrees.. before going down again.

[Boosted LS1]

rev-erend said:

Boosted LS1 said:

toltec said:

One trick I was told about, not tried it myself though, was to form a soap bubble across No.1 spark plug hole and watch the size change to find TDC.

That sounds quite novel but you'd be better using the balloon on a tube method. It's deadly accurate.

I just put something stiff but soft in the plug hole, small plastic tube and watch it rise to tdc whilst I rotate the crank using a long bar.

Boostewd

So is TDC when the piston first reaches the top - as I guess it seems to stay there for say 5 ~ 10 degrees.. before going down again.

Shucks, have I been found out? So, no balloon sales?

Tdc is half way in between going fully up and going down so ideally you would use a dial guage. If you're careful you could use a dial guage and a gutted spark plug or similar adaptor inserted into the plug hole. Be careful because the guage is set an an angle to the piston! For setting timing and stuff like that the exact spot isn't that important as you'll probably find a sweeter setting just by advancing the distributor slightly In otherwords, imo, don't spend a week finding tdc accurate to half a degree on an installed engine. A simple tube going up, stopping and then going down is sufficient to get you in the ballpark.

Boosted.

[dickkark]

dickymint said:

Would it not be dependant on a good piston ring seal?

If the rings are worn that much that they wont blow up a balloon, all the tuning/timing in the world wont help!

[dw350i]

Having fitted the distributor the timing was 9 degree, so I attempted to set it to 8. Initially i turned the dizzy the wrong way and sent it off to 12 before resetting to 8. The odd thing was that at 12 the engine had a sweeter sounding idle than at 8. Went out for run in it, seems OK. Can you hear if it is only slightly pinking over the sound from the exhaust? The new engine has still done only 600 miles so I am hoping this why it still does not feel that fast, that said as I go to work using a more modern jap 2500 V6 engine car maybe it never will.

[Boosted LS1]

One of my rovers absolutely loved 16 degrees of static advance, so much so that it would wheelspin off the line at every opportunity. The downside was that sometimes I'd get starter motor kickback when cranking .

I reckon it's good to set the advance with a vacuam guage aiming for the highest reading. Then dial out any centrifugal advance which may cause pinking or worse. You need to open up the dizzy to do this or buy a mallory unilite.

Boosted.

[shpub]

When finding out TDC, remove the plugs from the other cylinders. Makes life or turning the engine over a lot easier.

[dickymint]

dickkark said:

dickymint said:

Would it not be dependant on a good piston ring seal?

If the rings are worn that much that they wont blow up a balloon, all the tuning/timing in the world wont help!

Thats what i meant

[hamish400]

As there is very little piston movement around top dead centre it can be difficult to accurately determine TDC with a single measurement.

To accurately find top dead centre, use dial gauge (or ruler or similar) through spark plug hole.
Turn engine until near top dead centre (say approx 10 or 15 degrees before TDC) and take dial gauge reading (or mark ruler.)and put mark on crankshaft pulley in line with a fixed point.
Turn engine beyond top dead centre until same gauge reading measured. Put second mark on crankshaft pulley.

TDC is midway between the two marks you have made.

Rgds
Hamish