compression testing RPM

[jrisingmoon]

I was reading in the Haynes manual that the engine needs to be at 200 rpm in order to compression test the engine. Is this info accurate and is there anyway to set the engine to 200 rpm without a timing meter or is a meter of some sort necessary?

 

[94f450sd]

warm engine to operating temp,remove all 8 glow plugs,disconnect the FSS.install compression tester and adapters watch gauge as you crank the engine over with the starter.stop cranking when the gauges stops going up thats your reading

 

[jrisingmoon]

once the engine is warmed to operating temperature, shut the engine off, remove gps, and proceed as written above?

 

[94f450sd]

yup.the haynes mauals arent as good as they were when they first came out.the newer books from them really suck lately

 

[Mr_Roboto]

They are just saying that if the engine isn't cranking at normal speed, that your readings won't be right.

Say your batteries are in bad shape and the starter slows down significantly between reading #1 and reading #8, you will have progressively lower readings.

Having a battery charger hooked up, or booster cables hooked up from a running vehicle should help minimise voltage and cranking RPM drop. The engine will turn over pretty easy since there is only compression at one cylinder at a time.

 

[jrisingmoon]

I need a compression gauge, too. Recommend any? I know I'll need an adapter and a gauge that reads around 500+ psi.

 

[Diesel JD]

Yup, you just described your criteria, check over at Northern Tool, I have one of their Hoffman Gauges, they work well. Don't kid yourself though,a compression test isn't as easy as you think, and doing it on a hot engine is not an easy task. If your starter is in good shape, batteries as well, and you remove all 8 glow plugs, your readings will be dea on. Proceed with caution with the Haynes manual, some of their advice will hurt you. Like their oil cooler overhaul is bad info, maybe a couple other things... good luck.

 

[jrisingmoon]

I try to take what I get from Haynes with a grain of salt. usually I read it, get an idea of what all is going on then come here for a more detailed and accurate advice.

The starter is new and the batteries are 750 cca and new. I'd like to get stronger batteries but those were what I could afford.

 

[RLDSL]

Keep a battery charger handy, even with the huge 1190 ca batteries i've got, by the time I got to #6 with three readings on each hole ,it was slowing down enough to alter the reading. Had to stop and give it a charge. boosted the reading by about 50psi

 

[Diesel JD]

One thing is, there's no need to wait till the gauge quits going up, crank for about 6 compression strokes, you'll want to see the needle jump off the line real fast, taht indicates a good seal on your rings. You'll pretty much top out at 6 strokes. Additionally, you must do the same number of compression strokes for each cylinder. It would also be prudent to do a 2-3 minute cooldown between cylinders. What burns out batteries and starters is an amperrage drop, voltage increase, heat increase. Back to simple physics...voltage adn amperrage are inversely proportional. This is the same tactic we use when bleeding air. If your batteries are healthy, a simple compression test should not wear them down. 750 CCA is good, that's about what my Interstates are. More is probably not bad, but you'll never have a problem with those batteries as long as they are healthy and your charging system works.

 

[jrisingmoon]

If I get the engine to running temp, could i remove the IP and then compression test the engine? I would think that spilt fuel would be a problem but I'm sure there are other things to consider as well. I'm going to do it anyway so I figured if I could go ahead and get things rolling once I get the gauge and adapter.

 

[Mont91]

With the IP off there would be nothing to hold the IP drive gear in place so it would bounce around in the housing while cranking. Not a good thing.

 

[Mr_Roboto]

Just unhook the FSS wire. No fuel to spill.

 

[jrisingmoon]

The only way I can get the IP out is by removing the IP, the timing gear, the timing gear cover and the hard lines as one big unit and pulling into the van cabin. Anyway, I'll unhook the FSS wife and go from there.

 

[Dalvaras]

The only way I can get the IP out is by removing the IP, the timing gear, the timing gear cover and the hard lines as one big unit and pulling into the van cabin. Anyway, I'll unhook the FSS wife and go from there.

you do not want to remove the timing gear and cover just remove the round plate on the front of the cover and the remove the 3 bolts that hold the IP to the gear...oh and yes just unhook the FSS wire to do the compression test