Rip d24

[bigvolvoboy]

I did a compression test today and tragically found out my engine is done for. cylinder 1 and 3 are only hitting 110ish psi but luckily I have a spare engine. I'm also going to be manual swapping it at the same time to kill 2 birds with one stone. Will the m46 mount up to where the auto was or do I need different mounts?

[ngoma]

Maybe, maybe not. What were the other cylinder PSI? Could be something as simple as valve adjustment. Did you check the valve clearances?

How long did the engine sit unused? I had one that sat for year. Not enough compression to even start, tried for weeks. Rings were dry. Poured 1/4 teaspoon motor oil in each hole, it literally roared to life within 1.5 seconds on the starter!
Startled everyone in the shop.

Very strong runner after that.

[bigvolvoboy]

Realized after I posted this I never checked the valve clearance so I'm going to do that today. The other 4 cylinders read 350ish and it has sat for years without running. The previous owner replaced the head due to it cracking or something like that so there could be a chance that its just the valve clearance.

[bigvolvoboy]

Checked the clearance and wasn't even able to get the smallest feeler gauge of 0.04 mm under the intake cam. I think the camshaft might be ruined as it is in pretty bad condition. Looks like I might need new camshaft and discs.

[ngoma]

Originally Posted by bigvolvoboy

Checked the clearance and wasn't even able to get the smallest feeler gauge of 0.04 mm under the intake cam.

Good work.

Yes that is way tight. Is that one of the low-compression cylinders?

[bigvolvoboy]

Yea that was the first cylinder so I ordered some smaller discs and hopefully that’s they reason compression is so low. Also I don’t know too much about diesels but wouldn’t it still be able to start off 4 cylinders or does it need all 6? Just asking because I wasn’t able to get it started at all.

[v8volvo]

Nice, sounds indeed like you are on the right track.

These engines can be funny about starting with a couple cylinders down. I think it may depend on which particular cylinders are dead. In your case 1 and 3 are also positions 1 and 3 in the firing order. The engine may not be able to keep enough crankshaft momentum going with one cylinder (#5) trying to hit in between those two dead misses. And it only has three consecutive cylinders that can fire, so that's only half the engine (6,2,4). This is speculation but I think it might have a better chance of starting if it was two consecutive cylinders that were dead, e.g. 1 and 5, so that the rest of the engine could run on 4 in a row. But even then that would probably depend on other variables also, like ambient temp, compression on the other 4, pump timing, starter and battery and injector condition, etc. And of course the glow plugs on the 4 that have compression.

Anyway that's a long way of saying no, it would not be that surprising if two low cylinders prevented it from running, considering those factors above. One dead hole doesn't matter much but two or more somehow suddenly matters a lot more than one might expect. It's a fairly familiar fact to many of us here that starting these engines, assuming all else is in good shape, works like this:
6 glow plugs working: starts instantly, effortlessly, cleanly
5 glow plugs working: starts easily but rough and smoky until the one dead cylinder starts hitting
4 glow plugs working: can become very hard to start, sometimes impossible depending on other engine/environmental factors and perhaps on where in the firing order the dead cyls are
3 glow plugs working: engine almost always is impossible to start except by dragging the car (with standard trans), unless ambient temp is very warm and engine is in exceptional condition otherwise

Adjust those valves and see what happens! A seat of the pants leakdown test is always good info in this situation too. Dismantle compression tester, build air line adapters as needed apply shop compressed air to suspect cylinders (with the cylinder being tested at tdc with valves closed), and listen/feel for where most of the air is escaping: intake manifold, exhaust tailpipe, crankcase, or coolant recovery bottle. You don't need a leak down gauge to tell you fundamentally where your issue is coming from. Then you can adjust valves and observe the difference, if the leakage was found in inlet or exhaust areas.

[ngoma]

Originally Posted by bigvolvoboy

Also I don’t know too much about diesels but wouldn’t it still be able to start off 4 cylinders or does it need all 6? Just asking because I wasn’t able to get it started at all.

Here, bookmark this sticky, you will need to study it soon:

Hard Starting

[bigvolvoboy]

I just realized I never tested the glow plugs which could honestly be the main issue. (Kind of put it off because you have to remove the IP to access glow plug #6) I'll make sure to test those and buy replacements if necessary. Thanks for the advice and linking that Hard Starting thread. Worse case scenario I got the spare engine .

[bigvolvoboy]

Also what's the cheapest place to get the shims from?