Checking TDC

RogerD · Post by **RogerD** » Tue May 19, 2015 6:13 pm

I'm about to mark my crank pulley with TDC / check the existing mark (if one exists) in preparation for installing a trigger wheel. Never done anything like this before.

I've got a dial gauge. I've also got plenty of long thin screwdrivers!

To ascertain TDC , as I understand it:

Remove spark plug from cyl no.1 and either put DTI gauge or a long scredriver down it.

Turn engine by hand until piston reaches top (DTI gauge stops) AND dizzy is pointing at No.1 (is this the same as checking both rockers are closed?) - mark this point on crank pulley.

Now turn engine other way round until same happens, and mark the moment the piston stops climbing.

Now take dead centre between both marks as my TDC.

Sound correct?

I've not looked yet but will a standard DTI gauge reach down enough to hit a piston. Can't imagine it will?

ChrisJC · Post by **ChrisJC** » Tue May 19, 2015 7:13 pm

Your basic strategy is sound.

I would look to make an extension on the DTI.

Chris.

DEVONMAN · Post by **DEVONMAN** » Tue May 19, 2015 7:20 pm

You don't have to worry about the dizzy position or the valves.
TDC for No1 is identical even for the exhaust stroke.

Regards Denis

RogerD · Post by **RogerD** » Tue May 19, 2015 8:53 pm

Ahh cool - read some threads about getting the combustion stroke. Perhaps I'll need it for the Megajolt?

Extension on the DTI is a good idea. I'll knock something up

DaveEFI · Post by **DaveEFI** » Wed May 20, 2015 9:07 am

RogerD wrote:Ahh cool - read some threads about getting the combustion stroke. Perhaps I'll need it for the Megajolt?

Extension on the DTI is a good idea. I'll knock something up

If you're using wasted spark, you don't need to know the cylinder phase. Just crank position.

mgbv8 · Post by **mgbv8** » Wed May 20, 2015 8:39 pm

To find true mechanical TDC I have an old spark plug which I pulled the middle out of (remove earth strap and broke out the centre electrode) and brazed in an old bolt which I ground the end to a round ish shape. The bolt thread sticks out about 20mm from the plug end. I screw this in and rotate the engine one way until I feel the piston hit the bolt. Then I mark the crank pulley. Rotate in the opposite direction until the piston hits the bolt again and mark the pulley. The centre point between these two marks is TDC for that engine

bigaldart · Post by **bigaldart** » Wed May 20, 2015 9:24 pm

Perry wins the prize, KISS works every time.

Alan

DEVONMAN · Post by **DEVONMAN** » Wed May 20, 2015 9:36 pm

bigaldart wrote:Perry wins the prize, KISS works every time.

Alan

Got one the same in my special tool drawer.
That porcelain is bloody tough to remove though.
But it breaks easy when you don't want it to say when you accidently drop a plug.

Regards Denis

RogerD · Post by **RogerD** » Wed May 20, 2015 9:44 pm

Cheers. I read about the sparkplug method, but I have a DTI gauge so I used that.

I put (taped damn firmly) and extension on it (a long m3 bolt) and put it in cyl 1 though the plug hole.

Then cranked the engine by hand with a socket on the pulley.

Kind of interesting really. At first my bird did it by eye while I turned the crank (no DTI - just eyeballing the piston with a lamp through the plug hole) and we ended up agreeing TDC was bang on the markings already on the damper.

Then with the DTI, after many many many extra re-checks, I ascertained TDC is 4.5 degrees after the marked TDC.

It's amazing how fast the DTI gauge flips from rising to falling. Even turning the crank as slowly as possible it climbs...climbs ...climbs... slows down a tiny fraction...then immediatly drops!

SuperV8 · Post by **SuperV8** » Thu May 21, 2015 12:43 pm

I've just made my own spark plug piston stop tool out of an old spark plug.
You can just cut the radius from the top of the metal body off with a hacksaw and the porcelain piece will easily tap out. Then bolt a cap head bolt in and bobs your mothers brother.

Tom

mgbv8 · Post by **mgbv8** » Thu May 21, 2015 10:18 pm

DEVONMAN wrote:
bigaldart wrote:Perry wins the prize, KISS works every time.

Alan

Got one the same in my special tool drawer.
That porcelain is bloody tough to remove though.
But it breaks easy when you don't want it to say when you accidently drop a plug.

Regards Denis

The real funny thing is that I've made 4 of these now. I've lent them out to various folk and never got them back

unstable load · Post by **unstable load** » Fri May 22, 2015 7:14 am

mgbv8 wrote:The real funny thing is that I've made 4 of these now. I've lent them out to various folk and never got them back

Well, with a V8, you can still please 3 more mates and keep the last one for yourself.....

mgbv8 · Post by **mgbv8** » Fri May 22, 2015 7:16 pm

unstable load wrote:
mgbv8 wrote:The real funny thing is that I've made 4 of these now. I've lent them out to various folk and never got them back
Well, with a V8, you can still please 3 more mates and keep the last one for yourself.....

Ha Ha!! Thats true I suppose

unstable load · Post by **unstable load** » Sat May 23, 2015 4:50 am

So, can I send you my address..........?

mgbv8 · Post by **mgbv8** » Sat May 23, 2015 9:23 pm