@@midwestmotoring that's for sure. I'm battling a front windscreen install and IRS mount replacement currently. Hopefully have the front and rear windscreens back in and Jag roadworthy this weekend.
Depends on the carburetors. In an SU or Zenith-Stormberg, the air piston is still going to be mostly or fully down--so even with the throttle open it won't make a significant difference in compression readings. With a Weber, that's a different story since they don't have an air piston and therefore don't operate the same way. Also, remember that the gauge probably isn't super accurate anyway--especially since the dynamic compression while the engine is running is likely to be quite different than the static pressure from just turning it over. What we're looking for is a comparison between the different cylinders; not the absolute compression reading.
It's usually best to replace it, but in a pinch not absolutely necessary since it's not under that much pressure. If the gasket doesn't break, I can't say I've never just reused it.
Hey, another rookie question - Should I block off the fuel lines before I compression test? I have an older pertronix ignition, so my initial plan was pull the negative wire off the coil and then I started to overthink things and wonder if I'm load the carbs up with all the cranking over. Thanks again!
No need for the zip ties on 4. What was your choice of plug gap ? Not enough revolutions on the compression check. Take your compression check after adjusting valves. The professional way to check valve gaps is re-torque the head first. What is your figure for valve clearance ? There is another technique that requires engine rotation only twice. Carb adjust? Timing? Points adjust presuming not electronic.
Great video. Yea, don't want to squeeze the electrons. LMAO. 🤣
You know that someone's going to hear me say that and take it seriously, right?
You do need a sense of humor to work on these things though....
@@midwestmotoring that's for sure. I'm battling a front windscreen install and IRS mount replacement currently. Hopefully have the front and rear windscreens back in and Jag roadworthy this weekend.
Remember to wedge the throttle pedal to the floor. You'll get a big increase in compression
Depends on the carburetors. In an SU or Zenith-Stormberg, the air piston is still going to be mostly or fully down--so even with the throttle open it won't make a significant difference in compression readings. With a Weber, that's a different story since they don't have an air piston and therefore don't operate the same way.
Also, remember that the gauge probably isn't super accurate anyway--especially since the dynamic compression while the engine is running is likely to be quite different than the static pressure from just turning it over. What we're looking for is a comparison between the different cylinders; not the absolute compression reading.
Great vid! Rookie question, do you need to worry about the valve cover gasket if you're taking it off?
It's usually best to replace it, but in a pinch not absolutely necessary since it's not under that much pressure. If the gasket doesn't break, I can't say I've never just reused it.
@@midwestmotoring Thank you!
Hey, another rookie question - Should I block off the fuel lines before I compression test? I have an older pertronix ignition, so my initial plan was pull the negative wire off the coil and then I started to overthink things and wonder if I'm load the carbs up with all the cranking over. Thanks again!
No, the floats in the carbs will stop the fuel flow. No need to block them off. As for pulling the wire, that'll work and is a good idea.
No need for the zip ties on 4.
What was your choice of plug gap ?
Not enough revolutions on the compression check.
Take your compression check after adjusting valves.
The professional way to check valve gaps is re-torque the head first.
What is your figure for valve clearance ?
There is another technique that requires engine rotation only twice.
Carb adjust?
Timing?
Points adjust presuming not electronic.
I know, but my OCD would never let me get away with that. :)