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TR4/4A Finding compression stroke


Jedi Hopeful
Country flag
I have searched and don't really find the answer for this although I am sure it is here somewhere. I need to mount my distributor from scratch as someone (me) did not adequately prepare when it was removed. The instructions are saying I need to be at TDC on the compression stroke. I know TDC from the flywheel mark but I understand it is not the same. I placed a piece of paper over the spark plug hole and can see when it blows out but there must be a more accurate way of determining this. My valve cover is off, and as I said I have access to the flywheel mark. My timing cover is off as well but I have new unmarked gears. Thanks Bruce


Country flag
The piston comes up and pushes the paper away at that point you stop spinning the engine and look for the 2 marks; one on the timing chain cover and the other on the pulley. Now by hand by turning the fan/pulley you Line those 2 marks up and you are done. The mark on the pulley will probably go past the mark on the cover by about a one inch or maybe an inch and half, so you have to bring them back to TDC compression stroke


Obi Wan
Country flag
If your timing cover is off, your crank pulley is also off, so you don't have timing marks that are normally used. I think your only option is to put a screwdriver into the #1 plug hole and LIGHTLY feel when the piston is at the top of its stroke. If the #1 valves are both closed, that's TDC on the compression stroke. For installing the distributor, that should be good enough.


Country flag
I'm not familiar with the TR4 engine, but is it even possible to install the distributor any way but the way it was removed ?
I ask because the TR6 distributor shaft has a slightly off set driven dog which will seat back in place in the engine oriented only one way.

FWIW, if you do need to distinguish between TDC at compression and TDC at exhaust, I wouldn't rely on the paper as an indicator. The piston will be pushing air out of the cylinder on both strokes.. and there be air coming out an open spark plug hole as well as thru an open exhaust valve on the exhaust stroke...more thru the path of least resistance.
Closed valves would be the best indicator IMO.


Senior Member
Country flag
Watch the #1 valves. Exhaust will open and close, then intake will open and close. At intake closure, you are at about BDC on the beginning of compression stroke. Turn the crank another 90 degrees or so and put a probe (small screwdriver, length of coat hanger, dowel, or something rigid and plastic) and feel for the piston. Turn it a little more and feel again. As it nears the top, you can leave the probe in the hole and watch/feel it crest and begin downward. The highest point is TDC compression. Another clue is the short radian of reduced effort to turn the crank. This is because all crank throws are at top or bottom and you are moving the rod big ends side to side rather than up and down.


Country flag
These both work - a HF compression tester and a homemade setup with a spark plug boss on the right (with a rubber seal) and the finger off a glove as a balloon:



Jedi Hopeful
Country flag
Ok thanks for the advice to all. Hopefully I can get it with your suggestions. On a related note I have in addition to the new unmarked timing/crank gears decided to convert to the narrow belt option which of course includes a new crankshaft pulley (unmarked). Can I use the arrow on the flywheel for TDC and then drill my new pulley (as the original) at the marker on the timing cover for TDC? Bruce


Country flag
Yes as long it is TDC compression. I do not see why not. you can look inside at #1 with a flashlight to see when it is up.
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