The 84 SD has a shake and didn't start the other day. I'm thinking compression and leak down tests are or will soon be in order.

Prior to the current no run situation and for other legitimate reasons valves have been adjusted, rack damper is new, Greazzer reworked the injectors, motor mounts were shot and have been replaced, engine shocks were removed and examined & fuel filters have been changed.

Have I missed anything except injector pump delivery valves and compression?

I'll deal with the starting issue first since it started easily until recently. I thought it might be the glow system but plugs ohm ok and all get power from the relay. I'll do more tests to be sure that system isn't the problem.

What is a good compression gauge for infrequent use? I glanced at Harbor Freight but those don't have very good reviews. Search results for: 'compression gauge'

What size and thread pitch are the injectors? I want to be sure before buying that the gauge fits.

__________________
85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

You might check this one out.

Super price on Tool Aid 34900 at ToolTopia.com


Whichever you use, remember it is not unusual for a diesel engine to exceed 350 P.S.I. DRY and COLD which is how you should test them.

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

MY HF gage set is fine though I can't speak to the accuracy of the calibration. Like most of us, I don't use it too often but it's nice to have when you need it and you can't beat the price.

I found an adaptor in the kit that fits the glow plug holes and that's how I've done it. While the cal may not be perfect it's plenty good enough to show if there's a bad valve (that will be near zero) or bad rings (I'd expect a reading somewhere around 200PSI or less). From what I can gather, a fresh new engine would show 400PSI or so and the race engine is about 325ish across the board, maybe a tad higher (I'm going off my foggy memory here - actual values are in my build thread). Mutt's engine has at least 225K or so (came from a car with a broken odo) so I'd guess that's pretty typical for a high mileage old Benz.

And don't forget to check the cam. If a lobe is wiped that cylinder either won't fill or won't empty and either way that cylinder won't make power. All it'll cost you is a cam cover gasket which is likely to need freshening up anyhow.

Another thought: If you have access to a bore scope (HF has them for pretty cheap) you can check out a near-zero compression reading by pulling the injector on the bad hole and looking at the valves. Few bore scopes will fit thru the glow plug hole. You probably could see if a corner is missing off the valve w/o pulling the head off. Run that piston down in the bore so there's room for the bore scope - Diesel combustion chambers are pretty small at TDC! Then you can decide whether to pull the head or find a good used engine or......

EDIT: I went back and checked my build thread on BangShift. The compression check showed an average of about 350 with a highest of 360 and a lowest of 320. Not ideal but evidently OK (hey, it pushed me to almost 130 MPH!). The PO checked the back-up engine using his HF gage and the values were similar - both stock, high-mileage engines.

Dan

I have used a HF compression gage kit on my 3 OM617.952 engines. I haven't tested the gage against another, but seems reasonable. I read ~250 psig in most cyl when my 85 engine needed a block heater to start on cold mornings and had much blow-by. The replacement engine measured >400 psig in all cyl and showed almost no blow-by. My 1984 engine has a few cyl in the 300's and noticeable puffing from the PCV port. Thus, you could pretty much judge the rings from the blow-by. I recall paying ~$35 on sale for the kit. In all cases, I used the injector holes. Note that the results depend on the adapter displacing exactly the same volume as an injector. If using the glow-plug holes, I would first remove all the injector tubes for easier access.

I don't see how an endoscope could view the valves without first removing the prechamber, which I understand is non-trivial. Perhaps you could use a compression test kit to rig a leak-down setup and apply air pressure and see where a cyl leaks to (intake, exhaust, or crankcase), as is done for gas engines.

__________________
1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Good point on the prechamber deal - I had forgotten about that. Might be just as easy to pull the head at that point. I was thinking of my Cummins......

Dan

This engine has always had a shake at idle. Not bad but not right either. It has always started easily until the other day when it was under 20*F which may be a battery or glow issue. The engine doesn't have excessive smoke and loosening the oil cap results in the cap only jiggling a little. The engine didn't turn at the normal speed and seemed to have an easier then harder time turning over but I know the battery was low at that point.

The glow light didn't seem to stay on as long as normal so I compared plug resistance to a used but working plug that I had in the used parts box. All closely matched. I also swapped in another used glow relay since it was handy and easy. No change in the light and I did get close to battery voltage at the glow plugs. There was some voltage drop in the wiring but I don't remember exactly how much.

A seemingly small measured voltage drop is significant so I'll revisit tomorrow when I have some time. Car battery voltage - all you need to know

I'm really hoping there is nothing significantly wrong as I have too much stuff on my plate to take on a head or engine swap.

Is there an easy way to diagnose injection pump delivery valves?

__________________
85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

You should get not much higher than 11 volts at the glow plugs when they are powered up. Anything higher means one or more glow plug is not drawing full current. I would not trust an ohm meter measurement of a glow plug. An easy way to check if your glow plugs are all working is measure the current consumption with a clamp on ammeter. With 5 good glow plugs, it should surge to 100 amps and then steadily drop to around 80 amps when they are full hot (after around 10 seconds).

I bought my HF compression test set about 5 years ago. It worked ok at first but with more use, the readings got more and more inconsistent and would not hold. I did some leak testing and found the quick couplers do not seal well and leaks down. I replaced the quick coupler at the cyl head end with better and smaller quick fitting, eliminated the quick fitting at the gauge end, and it's been working great (does not leak down) ever since. Basically the only HF parts I kept was the bare gauge and the ends that screws into the head, and made it much quicker to use. I can take a compression reading in cyl's #1 thru 4 via the glow plug holes in less than 5 minutes each. # 5 takes longer.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

My HF compression tester had one dodgy bit but was otherwise OK. The 90 deg elbow broke, just won't take any stress at all. It was replaced with a 1/4"(I think, not certain, posted a thread about it) JIC elbow which has been perfect. Was about ten bucks at a local auto parts store.

You say the valves were adjusted, how long ago/how many miles ago was that, and how long had it been before then? If they haven't been done in awhile, you'll find they go tight again FAST(under 5k miles) as carbon on the seats wears off. Might be worth checking the valves again - at least that's where I'd start.

__________________
617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap

I bought a tester from JC Whitney's 25 years ago, it used the same (dimension wise) glow plug adapters as what Snap-on used. Then, they sold adapters for any glow plug motor ever made, I suspect.
Still works just fine.

__________________
"I applaud your elaborate system of denial"

It was warm (55 F) and rainy today. I charged the battery, glow light came on as it is supposed to and it started almost as normal and ran. At least there is nothing major wrong. I'll do more as time and whether permit.

__________________
85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.