M20B25 Little to no Compression

[Etharla]

Hi all, I hope you are all well in these crazy times?
This is a long winded one I’m afraid.
I’m at my wits end and need some technical help. I’m no mechanic but have been following some threads on the best way to change a timing belt on the M20B25 engine.
Based on what I read I decided to remove the engine and gearbox as one lump and took the opportunity to refurbish as much as I could when I had the unit out. I sent the head away for a pressure test, new valves, stem seals etc and it came back all shiny and new looking. I bought new water pump, timing belt kit, new gaskets etc and rebuilt the engine. I checked the timing by hand at least 12 times to ensure the TDC marks lined up and they did. The engine turned freely during this test. I then put the engine and box back in the car.
I decided to turn the engine over before connecting the exhaust just to ensure that it was firing and after a couple of turns she lit up but only for a few seconds then died. It would turn over and over but no fire. Firstly I checked the spark and changed the distributor and rotor, relays, fuel pump and changed the CRS but still no joy. There’s fuel on the plugs after turning it over so I assume there was fuel from the injectors. I then borrowed a compression tester today and found there’s only about 50psi on two cylinders and almost zero on the other four. The gauge is either faulty or I’m in trouble.
I then decided to check the timing as I assumed that I had slipped a few teeth but no all is well with the timing and still on the tdc marks after numerous revolutions.

Any suggestions or help appreciated...

Thanks,
Joe

[JungleGus]

Not much to offer here Joe - only thing I can think of is the reason it fired up may have been leftover fuel in the injectors or rail (assuming they weren't fully drained). Unsure about the low compression issue.

But if it helps - usually these things are one minor thing that is unplugged and all will be up and running in the near future. That seems to be more often the case for these cars than catastrophic failure. Keep the faith.

Cheers,
Gus

[boiliebasher]

I'm a bit concerned about the compression readings to be honest.
Could you borrow another one or potentially buy another one to double check the readings are correct?

That's what I'd be doing personally. If those low figures are correct, it's time to pull the head off again as something ain't quite right mate

When doing the compression test, pull the fuel pump relay so you don't wash the cylinder bores out with fuel and if you can open up throttle so the engine can breath in some air whilst testing the compressions.
Be sure that the gauge is fully seated in the spark plug holes and be careful to not strip the threads. I've seen it happen before.

I'm assuming that the engine was running fine before the rebuild? Double check those compression readings with a different gauge and report back if you can

[tha881]

Did you check the valve clearances once the head was torqued down?

[Etharla]

Thanks for the responses lads. I had removed the pump relay before testing but hadn’t the throttled opened. Yes, the engine was running sweet before I started to mess with it.

I was thinking of the valve clearances but assumed that the company that did the head would have set these up.

Would this be enough to get low readings and not starting???

Thanks,
Joe

[tha881]

It would certainly be wise to get the feeler gauges out asap! Even if they did the clearances while it was on the bench, they should be re-checked once the head is torqued down

[Etharla]

Well, so I checked the valve clearances and they didn’t take much adjusting to put right, I assume they were fine. Anyway decided to take the head off again to look for anything damaged and there doesn’t seem to be anything wrong there either.
I’m going to check down the head bolt thread holes to see if there’s something that would mess up the torquing procedure. It’s the only other thing I can think of right now, unless anyone else has anything to add???
Will a head that has had new valves and seals be difficult enough to turn or is this a sign of a bent valve ? If a valve is bent would you be able to see it or does the smallest of bend knock it out?

Also does anyone know the sequence the valves should be opening/closing or is TDC all I need to worry about?

At present the crank and cam are at TDC and number 1 &6 cylinder are up and the valves on 1 are closed but the valves on 6 are slightly opened. This doesn’t sound right to me.

Thanks again and any help appreciated.

Joe

[tha881]

Im no expert but he most logical answer is that the compression is being lost in the head somehow, and that can only be through 3 places - plug holes, valve seals or the head gasket itself. If the engine ran fairly well before the rebuild then it would suggest the rings are not the issue.

Is the camshaft standard and are you using the standard cam sprocket?

[Ukhozi]

Disd you do a leak test when the head was off?

With head off, turn upside down with plugs in tight.
turn cam so both valves on the cylinder to be tested are closed.
pour a little light oil, (do not use petrol due to fire risk) and see if there is any leakage past valve seats.
Repeat on all 6 .
It could be that you may have turned the crank over when the timing was out or the belt not attached and you clipped a valve edge.
Put the engine to TDC #1 AND LEAVE IT THERE.
Fit head with both #1 valves fully closed, cam lobes away from rockers.
Fit head, do not move cam.
Fit timing belt without moving crank or cam significantly, double check marks.

You don't say if your M20B25 has the early case mounted or later cam mounted distributor, in the case of early ones down below, make sure the rotor is at the #1 mark as well as the idler pulley drives the distributor, but only on early ones.

There are only two reasons for low comp', valves and rings.

[Brianmoooore]

pour a little light oil, (do not use petrol due to fire risk) and see if there is any leakage past valve seats.

I use paraffin, diesel or even heating oil.

Put the engine to TDC #1 AND LEAVE IT THERE.
Fit head with both #1 valves fully closed, cam lobes away from rockers.

My preference is to position the crank several degrees before TDC on 1 & 6, fit the head with valves as you say, then advance the crank to TDC, before fitting belt. Avoids any chance of contact between #6 valves and #6 piston as you are lifting the head into position

[Brianmoooore]

Compression test needs to be done with the throttle wide open. If the head is still on, I'd repeat the test and see what figures you get.

[Etharla]

Thanks again lads. I found the reason for the low to no compression and it’s one I’d never have thought of checking for before.
I had stripped all the alloy parts off the car to get them vapour blasted. Before refitting them I gave them all a quick wipe with WD40, to stop any surface corrosion. What I didn’t think of was the inside of the manifold. It was still full of glass media and had drawn itself into the head and on down in to the pistons. The actual chambers in the manifold were full of the stuff.
I’ll try and get round to building it back up again today and try turning her over.

Thanks,
Joe

[tha881]

Joe I would not fire that thing until you are absolutely sure you have removed all the glass media from the engine. If it's gone through the ports into the chambers that is bad news. I would consider removing the head and the sump and cleaning all the internals as much as possible. I'm not too clued up on the composition of the glass media but I would guess that it's very abrasive and very fine particles.

[DanThe]

As above, do not turn the engine, it needs stripping, the glass will be between the pistons and bores and the only way to get it out is to remove the pistons

[Brianmoooore]

AS ABOVE. Full stripdown required.

[flybynite]

As above, not only will everything need to come out but everything will need stripping and inspecting. That blasting media is some of the worst stuff you could get in an engine.

As it fired up momentarily the stuff could be anywhere. When the pistons are out I would be checking and cleaning the rings properly as the finer stuff may have got as far as the oil ring.

I once stripped a Ford pinto engine that had sand down the carb and we found the stuff everywhere

[Etharla]

I hadn’t read the responses until now and it’s not great news. As I didn’t see the responses I took a hose to the intake manifold and dragged a cloth through all the ports. I cleaned and sprayed WD40 through all the ports and rotated the cam and cleaned every valve. I did the same with the pistons and block. I got up this morning at 7am and rebuilt her and guess what she started first kick and purred like a kitten. (For about 20 seconds). Maybe it was lucky that the throttle pedal had disengaged from the shaft or I would have let it run on for a while. Back to the same issue now, she won’t start again. (Remember I hadn’t seen the posts before trying all this).

The positives out of this all are. Now I have a good idea how to strip and rebuilt most of the engine. Also now I get to finish the garden fence!

Thanks for all the help and comments lads, much appreciated.

Cheers,
Joe

[Etharla]

Hi everyone,
So I’ve eventually got round to stripping the engine after my stupidity and running the engine whilst full of blasting media. I would recommend that no one else tries this btw.

Anyway the block has to go back to the workshop to get reworked. The cylinders are all well scored which I assume is repairable as they aren’t deep. My question is if any considerable amount material has to be removed to put it right do I automatically have to change the pistons? I had assumed there would be a threshold where I would get away with oversized rings but don’t know if that’s even possible.

I’d love to hear what options I have from all you on here.

[flybynite]

Oversize rings are for oversize pistons in cylinders bored to the relevant oversize.

If the machine shop is able to just re-hone the bore you may get away with a set of new standard piston rings. (as long as the engine was standard to start with)

Machine shop should tell you what they were able to do. Good luck

[onthames]

Just don't let them fit sleeves

[Etharla]

Just don't let them fit sleeves

Oh I have experience with those in a few L120 Volvo loading shovels, not great by any means. I’m hoping a rehone but not feeling that confident when re looking at the bores.

Thanks
Joe

[Etharla]

Oversize rings are for oversize pistons in cylinders bored to the relevant oversize.

If the machine shop is able to just re-hone the bore you may get away with a set of new standard piston rings. (as long as the engine was standard to start with)

Machine shop should tell you what they were able to do. Good luck

Thanks, I wasn’t sure if it was possible to fit new rings with a slight increase in diameter that would work. I have the block completely stripped ready to bring to the workshop on Monday…

[martauto]

Any pics of the bores mate ?
For future reference like, if they are no good then this is a gauge to go by.
Then if they are OK then likewise.

Mart.

[Etharla]

Any pics of the bores mate ?
For future reference like, if they are no good then this is a gauge to go by.
Then if they are OK then likewise.

Mart.

Hi Mart,
It’s hard to get a good photo of them with my phone, but here goes.

Joe

[flybynite]

Any pics of the bores mate ?
For future reference like, if they are no good then this is a gauge to go by.
Then if they are OK then likewise.
Mart.

Unfortunately you can't really tell by photographs or even looking at them. Tried and trusted way I know is to see if they catch your nail when dragging it across them.

There are obviously better ways for more modern engines like using a profilometer but the fingernail hasn't got it wrong for me yet

[Etharla]

Any pics of the bores mate ?
For future reference like, if they are no good then this is a gauge to go by.
Then if they are OK then likewise.
Mart.

Unfortunately you can't really tell by photographs or even looking at them. Tried and trusted way I know is to see if they catch your nail when dragging it across them.

There are obviously better ways for more modern engines like using a profilometer but the fingernail hasn't got it wrong for me yet

There’s no scratches that are deep. You can’t see the original honing marks only vertical lines but when you run your hand down through the bore it’s quite smooth to the touch.

What about recommendations for new bearings?

Cheers,
Joe

[Etharla]

Just thought I’d post an update for anyone that’s interested. So I eventually got the wallet out and decided to rebuild the engine. I don’t know why but I went standard again. It was only when I finished that I thought of other options. Anyway, I’m left with a total rebuild as close to original as possible.

As per my last post the bores were too far gone and the block had to be reworked, I went for oversized Mahle pistons & rings and got the bores machined to suit. I also got the crank polished and did a complete bottom end rebuild. Unfortunately the lack of oil seized the top end too and it was too far gone to save. I had to buy a complete new head, springs, valves rockers, cam etc etc… I put all of this together in March and fitted to the car and after tidying everything up she started after a few turns and sounded sweet. I am currently in the process of running it in and just changed the oil after approx 200 miles. I opted for the Millars CFS 5W-40 as per the recommendation on the oil section of the zone. It continues to run well and fingers crossed it stays that way for a long time.

It’s been a long journey but well worth it to hear that engine purr again.

[flybynite]

I don’t know why but I went standard again. It was only when I finished that I thought of other options. Anyway, I’m left with a total rebuild as close to original as possible.

A well-running standard 325i is a nice thing to have and very underated in a world full of swaps and strokers.

I am currently in the process of running it in and just changed the oil after approx 200 miles. I opted for the Millars CFS 5W-40 as per the recommendation on the oil section of the zone. It continues to run well and fingers crossed it stays that way for a long time.

Probably too late now and not the end of the world if you did not but it is best to use a different oil for running in, I use cheap supermarket mineral oil and maybe change it once or twice before I put the good stuff in at 500 to 1000 miles Depends on what I find in the oil I drain and the filter.

Good you have got it back running

[Etharla]

Thanks for the response. I used a standard millars trident 5w-30 for the initial run in. I did notice when I drained the oil that it had like a marble effect through it. I didn’t know if this was from initial wear of the bores or rings but intend to keep a close eye on it. I was conscious that I had used a cheap Crossland filter too and wanted to get it out of the car ASAP.

Do you think the marbling is something I should be worried about? Does it sound like premature wear due to the oil I used? Suppose a cheap filter wouldn’t have helped if it didn’t have a non-return valve. The crossland filter was 99p from eurocarparts!!!

[flybynite]

Who built the head and the bottom end? Did they use assembly lube? that can show in the oil when drained. It is one of the reasons I change the oil a couple of times. As long as the oil does not look like it has glitter in it you are fine.

Again, a bit late after the fact but did you run the engine up on the starter till you got good oil pressure before starting? I tend to run them without plugs on the starter for a minute or so after the oil light has gone out. Makes sure oil is everywhere it needs to go.

If you are worried then FWIW change the oil again at 500 and see. Spent enough on the engine, extra oil change or two is cheap insurance.

[martauto]

Very pleased you are up and running again and change the oil very often (filter too) even after you have run her in.
I buy mine in bulk ,20 litres a time and it saves a fortune !!!

Mart.

[Etharla]

Who built the head and the bottom end? Did they use assembly lube? that can show in the oil when drained. It is one of the reasons I change the oil a couple of times. As long as the oil does not look like it has glitter in it you are fine.

Again, a bit late after the fact but did you run the engine up on the starter till you got good oil pressure before starting? I tend to run them without plugs on the starter for a minute or so after the oil light has gone out. Makes sure oil is everywhere it needs to go.

If you are worried then FWIW change the oil again at 500 and see. Spent enough on the engine, extra oil change or two is cheap insurance.

Yea we used assembly lube when installing the new bottom end and crank and no sign of glitter. I turned over the engine a few times to help get the oil up round it and then I added oil to all the journals etc before firing her up. I wasn’t that sure if the oil was coming out of the pipe that spans the rockers. Would this be a spray or a drip? There’s loads of oil circulating when you take the oil cap off. I’ll change oil and filter in another 500 or so and see what the oil looks like then.

Cheers,
Joe

[Etharla]

Very pleased you are up and running again and change the oil very often (filter too) even after you have run her in.
I buy mine in bulk ,20 litres a time and it saves a fortune !!!

Mart.

Hi Mart,
Do you use the CFS 5w-40? I have the 20 litre drum of the trident 5w-30 and run it in an F30 330d, Audi S4 and A1 but wanted to put CFS in the E30.

How often would you change it? This car has covered more miles during run in than it has in the last 15 years.

Cheers,
Joe

[martauto]

If it`s good enough for them cars it will be fine for the e30.
"Brianmoooore" used to say that supermarket oil would be high tech for when the e30 was out.
I change my oil and filter twice a year on the e46 whether I do high miles or not, it`s still a cheap commodity for what it does.

Mart.

[Etharla]

If it`s good enough for them cars it will be fine for the e30.
"Brianmoooore" used to say that supermarket oil would be high tech for when the e30 was out.
I change my oil and filter twice a year on the e46 whether I do high miles or not, it`s still a cheap commodity for what it does.

Mart.

I’ll maybe just stick with the trident then. What’s your choice of filter?