Can I do a compression test on the 7.3l while its on the engine stand? i've only ever done them with a starter but I was thinking if I pulled all the GP's I might be able to spin the motor with a breaker bar. I just didnt know if I could spin it faster than it would leak down.

 

you could just bolt the adapter plate to the motor then us the starter.

 

No way can you spin it fast enough with a breaker bar! Like Matt said, ahh, just thought about it. It's on a stand by the bell housing. You'll have to take it off the stand and bolt the trams adapter on it. I personally would not bolt it back to the stand. Seems like to much stress on the bolts and housing. Maybe I'm just paranoid. I tested mine hanging from my tractor, but a hoist will work as well. Now two things for sure is make sure everything is torqued down and filled with oil or well lubricated. Then pull all glo plugs and spin the engine a few rounds to clear out the cylinders and make sure everything is freed up. When I first tried to spin my block over I used a good set of jumper cables and my tractor running. It made me look like a fool. I thought the starter I was using was bad but it turned out to be low amps. I ended up bolting up the batteries from my truck with some pre made cables to ensure a good connection. Then began to test each cylinder. Take note of how quickly each cylinder climbs. By the fourth or fifth turn it should be at max compression. Good luck. Is this an old motor? Rebuilt? Your original? I'm curious of results and milage "if any".

 

Most compression gauges use a check valve any way, so it will hold the results.

 

Its the motor out of my 205k mile truck. I had to part out the truck in a hurry so I didn't get the compression test done beforehand. I'm cleaning up the motor to install in a v10 excursion but would have liked to know if it needed rings. I'll have to pan off so I'll get a good look at the bearings at least

 

Wouldn't it be possible to use a high torque air ratchet to spin it at the damper bolt? Sounds feasible to me.
They do turn over easy with all the GPs out.

 

I am curious of the correct procedure of doing this in the truck. Is there by chance a write up on this???
This is all good info for later when I get my spare motor built though.
thanks

 

we do this on our little vdub motors. im curious to see if it'd work.
couple small squirts of oil for a wet test.


kurt

99 7.3 4x4 cc drw

 

I'd use the truck starter, even with using the vehicles starter I have seen motors that need to turn over up to 10 times to get an accurate reading. I would think turning over anything less than 100rpm would result in fluctuations in the readings.

 

Kurt,

Thanks for the input.

I think it would work. I've hand cranked at the damper pulley with the GPs out and it's not that difficult.

 

You will be surprised how much compression 1 plugged cylinder will make. I would not chance it! Your still not gonna spin it fast enough, I don't think!

 

What's to chance? Either it works or it doesn't. Worth a try.

It wasn't easy, but I've hand cranked a 7.3 with only 2 GPs out.

I have a 425 lb/ft air ratchet gun that I would try before hooking up a starter to an engine on a stand.

 

Yea but how fast does that impact turn when it's putting out that 425lbs? The 7.3 is alot of rotating mass. Sure the motor is easy to turn when it's turned slow. The valves will bleed down enough to allow you to turn. Same reason you can spin the motor when trying to break the crank pulley bolt or hpop gear bolt. Try it. I would be supprised if it works. I'm not arguing that I know cause I don't. I just can't get my mind wrapped aroun it working with the trouble I had spinning it with the starter. Think about how much gear reduction you have with the flywheel. Like a 10 speed bike.

 

David,

I understand all you are saying and agree.

I just think it's worth a try.

You never know till you try.

If I ever have a 7.3 on a stand I will give it a shot.

I'll let you know if it works.

 

Robin, I think you may do more harm than you think, I believe the impact wrench will over torque the crank bolt and damage the threads or berak the bolt.