recommend a diesel compression tester?

badwithusernames · Jan 1, 2020

In short, I have a few sick machines to diagnose. Borrowed a compression tester that was of very poor quality, and was not surprised when it didn't work. Turns out it was an amazon import special.. so I bought what I thought was an average quality set from OTC, which seems to (or so I thought) make decent tools. The gauge and fittings in the OTC kit were almost exactly the same as the first set that I borrowed! Same rubber trim, but a different color, same fittings with really rough threads, but a much nicer case and $250 to boot.
I returned it, didn't even try it.
Who makes a decent quality diesel compression tester, hopefully under the $300 mark? The gauge needs to read to 1000psi, and I'll need fittings for Mitsubishi/ Volvo/ Kubota.
Thanks in advance.
SD

Rob F. · Jan 1, 2020

All the one I have is is a gauge, check valve hose to connect to cyl and a pressure release (shraeder). Can you just make one with parts you have on hand?

john.k · Jan 2, 2020

I bought a proper Bacharach compression testing set in a box on the bay for $20,and the same guy had a GM injector sleeve inserting and reaming kit ,for which he wanted $50....I got the lot for the $50,plus $25 postage.Keep your eyes open,and dont whine when Chinesium is K.R.A.P..its meant to be to weaken the west.

atomarc · Jan 2, 2020

john.k said:
I bought a proper Bacharach compression testing set in a box on the bay for $20,and the same guy had a GM injector sleeve inserting and reaming kit ,for which he wanted $50....I got the lot for the $50,plus $25 postage.Keep your eyes open,and dont whine when Chinesium is K.R.A.P..its meant to be to weaken the west.

Me thinks the west has weakened themselves with K.R.A.P. If we weren't buying it..they wouldn't be producing it. It's the shits, but that's how it is these days...all about the dollar.

Stuart

steve-l · Jan 2, 2020

I have used an original Kent-Moor (DD) that worked OK, but in my opinion, there is no substitute for a leak down tester. I have a Snap-On one and I then make the adapter myself for any engine I need to test.

mmarquette · Jan 2, 2020

I agree used to do just compression tests but then started doing the leak down test. Compression tests can vary with battery charge starter age ect. Have done both on the same engine. While the compression showed ok but not great the leak down told me exactly what was going on. Cant remember but think it was bad exaust valves on couple of cylinders.

john.k · Jan 2, 2020

The simple fact is that none of the test stuff is necessary.....put a bar and socket on the crank nut and turn the motor over.....if it doesnt have bouncy compression on each cylinder,the head needs to come off...you can also clearly hear the hiss from leaking exhaust valves.....unless you are one of the enthusiasts who have a collection of GM 71 powered tractors with open pipes....then you cant hear nothin.

Garwood · Jan 2, 2020

I just buy the chinese ones and put my own hose and gauge on the injector adapter piece.

I've found them useful on diesels. Comp test is a good way to differentiate between rings, head gasket or valves.

Garwood · Jan 2, 2020

john.k said:
The simple fact is that none of the test stuff is necessary.....put a bar and socket on the crank nut and turn the motor over.....if it doesnt have bouncy compression on each cylinder,the head needs to come off...you can also clearly hear the hiss from leaking exhaust valves.....unless you are one of the enthusiasts who have a collection of GM 71 powered tractors with open pipes....then you cant hear nothin.

Sometimes you don't want to take the head off. You just want the piece of shit to run. IME, diesels don't need much for compression as long as it's enough to get it started. Sometimes determining if the engine actually will develop a few hundred PSI or if it's just flat toast or if it's a fuel issue thanks to our new Ultra High Bullshit Diesel Fuel. It can be pretty hard to tell and a comp tester is a simple way to make a solid decision which way to go when troubleshooting.

john.k · Jan 2, 2020

Reminds me of my customers...."I dont wan to feex him,I jus wan him to go"

badwithusernames · Jan 2, 2020

Garwood said:
Sometimes you don't want to take the head off. You just want the piece of shit to run. IME, diesels don't need much for compression as long as it's enough to get it started. Sometimes determining if the engine actually will develop a few hundred PSI or if it's just flat toast or if it's a fuel issue thanks to our new Ultra High Bullshit Diesel Fuel. It can be pretty hard to tell and a comp tester is a simple way to make a solid decision which way to go when troubleshooting.

This is exactly my reasoning. I have an excavator that is running like its dropping a cylinder. If I can verify that the compression is good across the board I'll send the pump and injectors out for service. But if it's got internal issues, I can get a used engine w warranty for cheaper than digging into it.
Thanks for the thoughts about good old fleabay. I forget to check it, and I looked after reading the responses. Managed to get a nice older MAC tools set, with a full set of 25 injector adapters for $120. I'm psyched!

john.k · Jan 2, 2020

We have just had Christmas shutdown....any machine owner worth his salt should have lifted the head for inspection and reconditioned /replaced valves/seats and springs and pop tested the injectors over the break,ready for the new year.

Garwood · Jan 4, 2020

john.k said:
We have just had Christmas shutdown....any machine owner worth his salt should have lifted the head for inspection and reconditioned /replaced valves/seats and springs and pop tested the injectors over the break,ready for the new year.

Right...

When the value of your excavator goes up and down depending on how much diesel is in the tank you could give a shit about the condition of the valves.

A shitty old 10k lb machine is worth about a buck a pound if it can crawl and dig. If I put $3k of work into the engine for no damn reason it means I lose my ass when I'm done with it and I sell it.

IME, heavy equipment engines are pretty disposable. Fix what breaks until the pump or the finals go and then part it out. An excavator with a new engine isn't worth shit if the pump is out or it needs tracks or finals.

ewlsey · Jan 5, 2020

A relative compression test can be done quickly and easily with an amp clamp and a basic oscilloscope. You just map the current required by the starter to compress each cylinder. A low compression cylinder will easy to spot. Then you can get more intrusive.

The catch with a diesel is figuring out which cylinder is the low one, since you have nothing to trigger the scope at a certain cylinder. I use a magnet stuck to the balancer and a simple prox switch hooked to the scope. You'll have to pull the valve cover and set cylinder 1 at TDC. It's simple with an inline engine. Just set the last cylinder valve overlap. V6 or V8 is more challenging.

badwithusernames · Jan 7, 2020

To follow up:
readings on the 3 cylinder mitsubishi diesel were: #450, #300, and #550. My borescope fit partway down the glow plug bore, so I managed to sort of peek into the middle center cylinder. Looks like a damaged piston, so a head R&R wouldn't do any good.
If the #'s were closer together, a head might work, and be cheaper. But, with these numbers this thing will be stripped for spare parts and scrapped.
Thanks for the advice, as always. SD

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