Plugs condition diagnostics

I've got a few problems with my b20, and I'm working on diagnostics to determine what's likely the cause, before tearing it apart. I need to keep it running for a bit before I can tear into it, as I am brining my regular vehicle in for some possible extended maintenance soon.

I've seen lots of pics of spark plug diag's...but it's hard to find high res ones. I thought perhaps someone here could point me to a better source for that info.

Couple steps taken/info gathered:
Low compression on rearmost cylinder dry, ok wet. Likely worn rings, or perhaps broken.
Metal shavings present under valve covers, in pooling areas of oil
low vacuum at idle
Low power - doesn't want to rev past 4000 or so
Stumbles upon accellerator press (likely bad throttle switch, but unplugging it makes it much worse, so I think it's helping a little, just not at the very bottom of the pedal travel).
Prev. owner, two mechanics stated cylinder 3 cam lobes worn out (I'm not sure which is #3...does it start with 1 in the front?)
Odd noise
Plug pics...not sure how to read these. And I'm not sure how to add them. My posting rules say I cannot post attachments. Any ideas on how to fix that?

Here's a link to a shared google album w/ the pics, and the notes on testing.
https://photos.app.goo.gl/3ah454CDGfHOI5KG3

The dirtiest one, looks like oil fouling...since it's got good compression, I'm guessing leaking valve seals....
The other ones...perhaps the plug temps are off? The white deposits, apparently flaking off, don't appear normal to me.

What year and model is your car and B20? I would also suggest getting a good basic reading reference about these cars so you can learn and have next to you when wrenching. Sure google and internet are good. But there is a lot of good knowledge to be had in books as well. A Haynes manual that covers your year Volvo is a good start. Plus it too has pictures of plugs with good explanations.

Yes, number one is at the front of the car. So the third cylinder back has issues. I would not convict the cam just yet. First you would want to make sure the rocker arms and pushrods are all good. The metal under the valve cover seems to tell me that the problem may be there. I've had broken valve adjusting screws on these before. As well as work out rocker shafts and rocker arms among other things.

Just a quick look at those plugs tells me that everyone of them is firing through either oil or too much fuel or maybe both. The one that isn't still looks like it's had some issues as it looks too far to the lean side with likely a vacuum leak on the intake gasket right near that cylinder.

If this is an older B20 without hardened valve seats for unleaded gas it may have valve recession into the cylinder head going on to contribute to the issues. I really hope you don't have to rely on this engine for too much.
Good luck with it.

vacuum leak at cyl 4, misadjusted valves (possibly a worn out guide on cyl 3), worn cam. remove the valve cover and spin it over by hand. It'll be obvious if its a worn cam.

The OP made reference to a throttle switch. That pretty much means a B20E or B20F which are speed X density fuel injections systems. Speed x density are pretty much unaffected by intake manifold air leaks (unless they are right at the gasket / injector and quite large). Like the others noted, the right plug is running lean for an engine of that vintage; but, I speculate more likely the injector associated with the plug is clogged.

Its not possible to be definitive as to whether the other plugs are suffering from a rich fuel mix or from oil fouling. To do an accurate mixture assessment you need to put in a set of fresh plugs.

If the cam and lifters are original, I would bet a beer that the contact faces at the cam- lifter interface is failing. My 1971 B20E had little flakes of steel missing from the lifter contact face and worn lobes. Volvo had some problems with the cam / lifter metallurgy on the B series which was fixed (?) by a late production change in the lifter design.

If the engine is a B20E, they tend to have a relatively low idle vacuum with the D cam.

Given the low compression on the rear cylinder and your description of the other symptoms, the engine almost certainly requires a rebuild. Only removal to measure the cylinders and bearings will determine whether it is a complete rebuild with a re bore and new pistons and bearings or just a ring job with work on the head.

As dl242gt alludes to, I would not be planning any trips in this car.

Thank you all for the suggestions.

It's a 73 145, and I'm unsure if it's a b20E or b20F.

I'm expecting the rebuild. Just trying to learn more about this as well during the process. I'll share more info as I complete more inspections.

A US model 73 145 would have a B20F with D-jetronic injection.

Thanks for the info. I also discovered a placard on the firewall also indicating B20F.

My manual states I need a special tool to remove the lifters to inspect them. Has anyone had luck with something like a magnet stalk? Or other commonly available tools?

If I was to replace the plugs, how would I determine if the deposits are from fuel being too rich or oil fouling?

With the head off a long pair of needle nose pliers or really good magnet will do it.

tonybaroni said:

If I was to replace the plugs, how would I determine if the deposits are from fuel being too rich or oil fouling?

Click to expand...

As a really gross rule of thumb, oil fouled plugs will tend to be shiny. Plugs fouled by a rich fuel mixture will tend to have a matte - sooty deposit on them. You can also have oil fouled plugs on an engine that is running rich and the oil fouling will mask the sooty deposits.

If your plugs have a black shiny finish to them I would not bother with new plugs since trying to get a mixture read is academic until you address the oil issue. Save the new plugs for after the engine rebuild.

Quick update.

I pulled the valve cover, and used a ruler to roughly measure valve travel on each valve. Half the valves had way less travel. The rest all had about the same. Pulled the engine. Cam lobes and lifter faces on those were crazy worn out.

Blueprinted the short block. Timing set, bores, and crank mains all out of spec.

It's very possible that fuel injectors were also contributing.

Decided to swap in something with more potential and ease of finding parts...so I am putting in a ?230, with 16V head...possibly a turbo too. Run with micro squirt.