Help- Low Compression & Oil Pressure 1.9 DG how far to rebuild?

[joshmc]

Hi All,

After some advice. Currently stripping down the 1.9 DG that was in my van. What led to this was: I did a compression test and got around 130 psi on all cylinders except cylinder 3 which was 60ish (first red flag). Then I did an oil pressure test and got 4 bar (sorry for mixing up bar & psi) cold at idle 0.5 hot at idle (with flickering oil light on dash) and 1.5 when revving.

So I thought (before a bunch of welding work) lets get the engine sweet. I've since stripped it down to the point where the heads are off. As in below pic: 
I'm a pretty amateur mechanic- and want to avoid tearing things apart that I don't need to/ will be very complex to get fixed and assembled. So I am trying to work out if I need to split the case. The valves on cylinder 3 look pretty burnt (pic at bottom), so I am going to get them out this weekend for a closer look, and probably replace and lap new ones in on that head. I am hoping this will fix the low compression as I think the heads look ok- but I welcome thoughts.

As for the low oil pressure do I need to split the case? Or will a new oil pump help? What am I looking for if I do split the case? Crankshafts and all of those components seem complicated to take apart and fix so just don't want to split it unless necessary. I am happy to do it, if I know what I am getting at.

Any advice will be greatly appreciate as I try to fix, and avoid wrecking my engine.

Thanks in advance, and sorry for the long questions!

Photo of suspect head (which is upside down): 
 

[silverbullet]

For the effort and cost, a top end rebuild usually leads to a bottom end failure. Low oil pressure means slack bearings so you must split the case and do everything.
I would build a stealth 2.1 using the 1.9 carb etc but I do have a choice of parts. Pistons are usually good to re-ring after a good clean, don't re-use worn barrels, a worn cam or old lifters. Cranks can survive without a grind - they have induction hardened journals - assuming they haven't been run with a loose pulley or flywheel.
The costs do escalate rapidly but thats wbx for you.
The hardest bit is finding a 2.1 cam and getting it timed.

[joshmc]

Ok cool thanks for your thoughts, sounds like the case will be split. To be honest im not sure its within my skills to fit 2.1 parts to a 1.9, that sounds quite advanced- will it not be easier to stick to 1.9?

Can you elaborate more on what you mean when you say slack bearings? Looking at bentley manual online, there are the following bearings: main bearings no 1. 2. 3. And 4. Along with camshaft bearings, con rod bearings and crankshaft pilot bearing, do all of those need replacing? Or will low oil pressure be caused by the main ones?

If a I split the case would I get away with replacing the 4 main ones and not messing with the con rods?

Sorry for the barrage of questions, just trying to understand the next stage of the build

[joshmc]

Not sure if anyone has any thoughts on this? Just trying to work out how many of the bearings need replacing/ what do I need to replace to help the oil pressure once I've split the case. If there is a guide already published on this I am happy to read that, but haven't been able to locate it on the forum yet.

Thanks!

[Dueller]

Oil pressure in its simplest terms, comes from the gap between the main bearings and the crankshaft

So as they age and wear the gap gets bigger hence lower oil pressure

A leak down test would have helped identify where the low compression fault was, head or rings. I've a brand new Autolinea head that leaked on no2 inlet valve so nothing can be assumed

You've done well to get this far with it as these motors are a bit awkward, I've a DF sat on a shelf I'm trying to avoid rebuilding, I'm more of an Aircooled guy

So with your engine there's different levels of rebuilding: Reuse what you have and only change the rings after cleaning up the barrels and pistons
The above and have the heads rebuilt too
The above and full strip, swap in new bearings
The above and have crank checked AFTER checking for bearing availability, no point resizing if not available
The above and change to an engle 100 camshaft
Change everything you can buy and rebuild
...or buy another motor ready to go

Like anything it depends how far you can go with money and skills/tools.

I only build full running engines for Aircooled now as I started on cheap rebuilds like we all do and progress as we evolve

Where are you based? Maybe someone near you to help/ advise further

[joshmc]

Ok thanks for the thoughts. I've got the case split today with relative ease so can now inspect the innards.

I'm going to look at the Haynes manual to see how to check for ware on cam/crank shaft. I will likely post a few photos here asking for some extra eyes.

My plan of attack at the moment is:
Replace all gaskets seals with a set from brickwerks
Re-lap valves on the cylinder that was leaking (with new valves if the old have visible issues) plus a touch up on the others if necessary
New rings on pistons
Replace crankshaft main bearings and oil pump- and try to check for excessive wear on the crank & cam. If there is wear then new plan needed.

Does that sound like a reasonably thorough approach for a DIY mechanic? Anything I am missing thats a no brainer to do while the engine is out? I drive the van pretty gently and just want it to be reliable as a weekend run around and for summer camping, so never going to clock too many miles each year.

I am based in north Somerset, but never known of a specialist garage in my area. 

[maxstu]

If you do decide to resize crankshaft and camshaft make certain you can buy the correct size bearings before committing to a regrind.

[maxstu]

As Dueller commented earlier....