TR2/3/3A follow up - TR3 broken pushrod &compression test

[eschneider]

Following up on my earlier post, thought the results were worth sharing for the next guy

https://www.britishcarforum.com/bcforum/ubbthreads.php/topics/678530/Re_TR3_broken_pushrod#Post678530

1) cylinder #3 had ZERO compression. When a couple of members posted that it could have been because both valves were closed, I thought no way, not possible.... but I did a leakdown test and promptly ate my shoes. I still don't get how there was ZERO compression, but....

2) I did wipe the tappet bores with a hi-strength magnet, installed the 3/8" pushrods, and of course adjust the valves. Compression is back to 150 psi.

3) I checked the oil passages in the head, and cleaned out the rocker assembly - so the next step is to fire the old girl up and watch for oil bubbling from the rockers. Now I know to wait for longer than 30 seconds before condemning the oil flow. I'll be pulling the oil pan to check for bits (it's leaking anyway)

I'll follow up after I've put some miles on it - but for the meantime thanks to all who posted, especailly TR3driver....

 

[Silverghost]

I may be wrong but when the intake valve opens, the piston draws the air/fuel mixture into the cylinder. Then the valve closes and the piston compresses that mixture and then the spark plug ignites it, propelling the piston downward and then the exhaust valve opens and the piston pushes the spent mixture out.

If both valves remain closed, the piston can't draw air in to compress when the intake valve closes and so you would get a zero reading on the compression gauge. This is also why the carb(s) have to be wide open otherwise the airflow is restricted and you get a lower compression reading.

I hope I got that right....