m20 b25 head gasket replacement . should i replace piston rings while im there?

[Gaffasgaff]

Hello . So i decided to strip the e30 m20 b25 engine few days ago whilst engine is in the car. I suspected the head gasket had failed due to exhaust blowing through the coolant. the head was also leaking oil so i though lets do it whilst on lock down . i did a compression test on all 6 cylinders 2 months ago i had not run the car for at least 9 months . here are the results
cylinder 1 -150psi
cylinder 2-150psi
cylinder 3-150psi
cylinder 4-110psi
cylinder 5-75psi
cylinder 6-160psi
after this test i dropped a bit of oil down cylinder 5+6. The compression has raised on cylinder 5-145psi and 5- 125psi.
the car was standing for a further 2 months and i decided to retest the compresstion on all 6 cylinders again before i started removing the head . Surprisingly all 6 cylinders are now reading 150psi.
i have now removed the head gasket and on closer inspection theres signs of exhaust and coolant mixture on the head.
now i have come this far would you recommend i replace the piston rings also or should i now leave it as the compression was in spec before i stripped the head.
I have never replaced piston rings before so im abit worried about messing it up . I have a haynes manual and it mentions filing new rings if its not with spec . ect . could do with alittle guidance on this . thanks

[Brianmoooore]

I stripped a damaged 200,000+ mile M20B25 a few years ago, carefully checking the wear on everything as I went. The damage to this engine, and the reason it was scrapped, was confined to one cylinder.
The ring gaps on all five other cylinders were still within new spec., and the honing pattern was still visible on the bore walls.
The only things I found out of spec. were the exhaust valve guides in the head, and the integrity of the valve seats. The valve guides were replaced, the valves refaced, and the valve seats recut and lapped, and the head was reused. The short engine was scrapped.
Conclusion: Your piston rings are probably fine.

[Speedtouch]

Check the cylinder head carefully for cracks - the M20B25 '885' heads were reknowned for this. Maybe get it pressure-tested, if you're unsure.

[Gaffasgaff]

Check the cylinder head carefully for cracks - the M20B25 '885' heads were reknowned for this. Maybe get it pressure-tested, if you're unsure.

Cylinder head has been sent to a local machine shop to have valves re-seated and skimmed and pressure test . will get results in a weeks time . thank you for your info much appriciated.

[Gaffasgaff]

I stripped a damaged 200,000+ mile M20B25 a few years ago, carefully checking the wear on everything as I went. The damage to this engine, and the reason it was scrapped, was confined to one cylinder.
The ring gaps on all five other cylinders were still within new spec., and the honing pattern was still visible on the bore walls.
The only things I found out of spec. were the exhaust valve guides in the head, and the integrity of the valve seats. The valve guides were replaced, the valves refaced, and the valve seats recut and lapped, and the head was reused. The short engine was scrapped.
Conclusion: Your piston rings are probably fine.

Thank you Brian . With your expert knowledge this has saved me the time replacing the rings . I will check to see if i can see the crosshatch pattern on the cylinder walls . if so i may just leave the rings and wait for the new gasket and head to come back from the machine shop . could you recommend a good head gasket kit ? so many on the market .

[Gaffasgaff]

Check the cylinder head carefully for cracks - the M20B25 '885' heads were reknowned for this. Maybe get it pressure-tested, if you're unsure.

if the head is cracked wrost case would repairing it be a good option ?

[tha881]

According to this its Goetze, if you want a full head set you can buy the Elring one from c3bmw. I would recommend get a genuine camshaft seal

It's also worth getting in touch with Neil at Corry Motor Services, my head wasnt cracked but due to condition it made more sense to buy a brand new AMC head from him

[Gaffasgaff]

According to this its Goetze, if you want a full head set you can buy the Elring one from c3bmw. I would recommend get a genuine camshaft seal

It's also worth getting in touch with Neil at Corry Motor Services, my head wasnt cracked but due to condition it made more sense to buy a brand new AMC head from him

Thanks. I will wait till I find out results after tests . If it's bad i will look in to the AMC head

[tha881]

If you've had gasket issues you will most likely need your head skimmed. Some common issues with these heads are cam journal scoring, and the water jackets can also corrode which narrows the surface between the cylinder and the coolant passages. Also worn camshaft and rockers.

The bottom end in theory should be fine, as your low compression readings are hopefully just due to the head gasket leak. When I did mine the bores looked fine and it was on 120,000 miles. Its back together and running strong. Brian may be able to advise on measuring the piston rings spec.

[Gaffasgaff]

If you've had gasket issues you will most likely need your head skimmed. Some common issues with these heads are cam journal scoring, and the water jackets can also corrode which narrows the surface between the cylinder and the coolant passages. Also worn camshaft and rockers.

The bottom end in theory should be fine, as your low compression readings are hopefully just due to the head gasket leak. When I did mine the bores looked fine and it was on 120,000 miles. Its back together and running strong. Brian may be able to advise on measuring the piston rings spec.

Hopefully the machine shop I took the head to will sort all that out . When i took the head there the guy was quite familiar with the head as he has done a few in the past . He mentioned them being prone to crack .
I am running evens waterless coolant also as most of the cars life its sat in storage so I thought I'd replace the coolant with waterless helps stop corrosion. I am hoping to get ot finished before lockdown ends . Would love to attend some e30 meets .

[Gaffasgaff]

20200522_110219.jpg

20200522_110219.jpg

If you've had gasket issues you will most likely need your head skimmed. Some common issues with these heads are cam journal scoring, and the water jackets can also corrode which narrows the surface between the cylinder and the coolant passages. Also worn camshaft and rockers.

The bottom end in theory should be fine, as your low compression readings are hopefully just due to the head gasket leak. When I did mine the bores looked fine and it was on 120,000 miles. Its back together and running strong. Brian may be able to advise on measuring the piston rings spec.

Hopefully the machine shop I took the head to will sort all that out . When i took the head there the guy was quite familiar with the head as he has done a few in the past . He mentioned them being prone to crack .
I am running evens waterless coolant also as most of the cars life its sat in storage so I thought I'd replace the coolant with waterless helps stop corrosion. I am hoping to get ot finished before lockdown ends . Would love to attend some e30 meets .

[Brianmoooore]

I would think twice about using waterless coolant. It is considerably less efficient at transferring heat, compared to water, and will promote larger temperature gradients in different parts of the head - just the conditions that cause cracking.

[Gaffasgaff]

I would think twice about using waterless coolant. It is considerably less efficient at transferring heat, compared to water, and will promote larger temperature gradients in different parts of the head - just the conditions that cause cracking.

Wow really . Ok . Will fill the system up with normal coolant then cheers Brian

[Brianmoooore]

This has come up on here before, and if you look on Evan's website, the info. is there, although not exactly highlighted. There are clues, such as I think there's something about the heater taking longer to work from cold.
Nothing conducts heat away better than water, and even adding antifreeze reduces that ability by a bit. Don't run pure water though, as the corrosion formed will act as an insulating layer, and stop the heat reaching the water as fast.

[tha881]

https://www.opieoils.co.uk/p-971-fuchs- ... trate.aspx

This is what I used. I've read that the m20 prefers blue coolant, and it's better use phosphate free, this ticks both boxes.

[Gaffasgaff]

https://www.opieoils.co.uk/p-971-fuchs- ... trate.aspx

This is what I used. I've read that the m20 prefers blue coolant, and it's better use phosphate free, this ticks both boxes.

Thanks brother . I will get me some of this once the heads back on . Will do a good flush before I fill it up .

[Gaffasgaff]

Update from machine shop . Head passed the pressure test . Now having valve re seated then hopefully back in the car . Really want to start using it again .

[Gaffasgaff]

Head back from machine shop rebuilt . Waiting to reinstalled with new head bolts . Will be using coolant instead of the water less as recommended by Brian

[Brianmoooore]

Lookin' good! Don't forget the two head locating dowels.
You wouldn't be the first to find them in the parts pot after torquing the head down.

Check that there's no oil in the head bolt holes on the block, and that all stud threads on the head are clean, and that a nut runs freely on them.

Just looked back at your underbonnet pics. and though of something I probably should have mentioned a while ago - the exhaust manifold is prone to warping, so ideally you would remove it and check the face that goes against the head with a straight edge, and get it machined if it isn't.
As an alternative, pull it against the head when you have fitted it, without the manifold gasket, and see if it sits flat, especially at the ends.

[tha881]

I would recommend a genuine bmw cam seal, I used the elring one and its leaking.

[Gaffasgaff]

Lookin' good! Don't forget the two head locating dowels.
You wouldn't be the first to find them in the parts pot after torquing the head down.

Check that there's no oil in the head bolt holes on the block, and that all stud threads on the head are clean, and that a nut runs freely on them.

Just looked back at your underbonnet pics. and though of something I probably should have mentioned a while ago - the exhaust manifold is prone to warping, so ideally you would remove it and check the face that goes against the head with a straight edge, and get it machined if it isn't.
As an alternative, pull it against the head when you have fitted it, without the manifold gasket, and see if it sits flat, especially at the ends.

Cheers Brian. Will do all of that . Do you know what size tap I will need to run through the holes on the block for the headbolts ?

[Gaffasgaff]

I would recommend a genuine bmw cam seal, I used the elring one and its leaking.

The guy who rebuilt the head bought the headkasket kit . I told him I want some thing that's gonna last . Told him I wanted gotze headgasket . For some reason I couldn't find it as part of a kit . Just the headgasket alone . So I told the shop to get me the gasket kit so that he could carry on with replacing the seals . He has replaced the cam seal also . More than likely he has replaced it with a elring one
.

[Gaffasgaff]

Lookin' good! Don't forget the two head locating dowels.
You wouldn't be the first to find them in the parts pot after torquing the head down.

Check that there's no oil in the head bolt holes on the block, and that all stud threads on the head are clean, and that a nut runs freely on them.

Just looked back at your underbonnet pics. and though of something I probably should have mentioned a while ago - the exhaust manifold is prone to warping, so ideally you would remove it and check the face that goes against the head with a straight edge, and get it machined if it isn't.
As an alternative, pull it against the head when you have fitted it, without the manifold gasket, and see if it sits flat, especially at the ends.

Cheers Brian. Will do all of that . Do you know what size tap I will need to run through the holes on the block for the headbolts ?

Got it . m10 1.5

[Brianmoooore]

Head bolt holes won't need a tap run through them - they've been in a clean environment for all of their lives, and will be fine. Just ensure there's no liquid in them, or a hydraulic lock may occur when the bolts are screwed in, which can be strong enough to crack a block.
It's the studs that have had their ends exposed and have had rusty nuts on them that need to be cleaned up.
An E30 head gasket isn't 'marginal' in any way, and any reputable/well known make will be fine, as long as it's fitted properly. If anything 'fails' on it, it will be oil weeping part way along the exhaust side, from the little elliptical bit where the oil feed for the head comes up the block very near to the edge.
Never known a cam seal fail, new or used.

[Bonymaenjack]

Head bolt holes won't need a tap run through them - they've been in a clean environment for all of their lives, and will be fine. Just ensure there's no liquid in them, or a hydraulic lock may occur when the bolts are screwed in, which can be strong enough to crack a block.
It's the studs that have had their ends exposed and have had rusty nuts on them that need to be cleaned up.
An E30 head gasket isn't 'marginal' in any way, and any reputable/well known make will be fine, as long as it's fitted properly. If anything 'fails' on it, it will be oil weeping part way along the exhaust side, from the little elliptical bit where the oil feed for the head comes up the block very near to the edge.
Never known a cam seal fail, new or used.

Sorry both to be an interloper into the thread but is there a recommendation to recheck the torque setting after so many miles of use after a replacement ?

[Brianmoooore]

Sorry both to be an interloper into the thread but is there a recommendation to recheck the torque setting after so many miles of use after a replacement ?

Head bolts are of the stretch variety, so there is no torque setting to check.

[Bonymaenjack]

Sorry both to be an interloper into the thread but is there a recommendation to recheck the torque setting after so many miles of use after a replacement ?

Head bolts are of the stretch variety, so there is no torque setting to check.

Thanks Brian I appreciate that you should replace the bolts whenever you take the head off but I never knew why,

[Gaffasgaff]

Head bolt holes won't need a tap run through them - they've been in a clean environment for all of their lives, and will be fine. Just ensure there's no liquid in them, or a hydraulic lock may occur when the bolts are screwed in, which can be strong enough to crack a block.
It's the studs that have had their ends exposed and have had rusty nuts on them that need to be cleaned up.
An E30 head gasket isn't 'marginal' in any way, and any reputable/well known make will be fine, as long as it's fitted properly. If anything 'fails' on it, it will be oil weeping part way along the exhaust side, from the little elliptical bit where the oil feed for the head comes up the block very near to the edge.
Never known a cam seal fail, new or used.

Cheers Brian . I will make sure the holes are clean of any fluid . Makes alot of sense what you are saying .
What would you recommend cleaning the block with before installing the gasket . I bought some wet and dry paper 1000-2000

[Gaffasgaff]

She's ready for the new head gasket to be installed . Hopefully should fly though it tomorrow . As Brian mentioned to make sure no oil in the head bolt holes . I had 2 holes full of oil . All clean now .

[tha881]

What did you use to clean up the block surface?

[Gaffasgaff]

400 wet and dry then gradually went 1200 . Used wd40 as a lubricant. I will make sure it's totally grease free before installing new head gasket .

[tha881]

Its cleaned up very nicely, I used gasket remover and a Stanley blade when I did mine, wasnt quite as spotless as yours. It might be worth pouring a bit of oil around the circumference of the piston rings and turning it over a little before you give it the final clean. It may not be needed but at least when you fire it up you know the bores are lubricated. I think I used acetone on the head and block surfaces.

[Brianmoooore]

It might be worth pouring a bit of oil around the circumference of the piston rings and turning it over a little before you give it the final clean.

Do this, wind the pistons down a little, and wipe the oil left on the bores upwards with a rag. You'll be surprised at how much debris comes out with the oil. Repeat until you get no more rubbish out, then lubricate again before fitting the head.

[Gaffasgaff]

It might be worth pouring a bit of oil around the circumference of the piston rings and turning it over a little before you give it the final clean.

Do this, wind the pistons down a little, and wipe the oil left on the bores upwards with a rag. You'll be surprised at how much debris comes out with the oil. Repeat until you get no more rubbish out, then lubricate again before fitting the head.

Head is now on . All the bolts have been replaced and torque down . 3 stage 1st 30nm on all 14 . Then 2nd stage 90 on all 14bolts . Then 3rd stage 90 degree again . 1 bolt on last tightening felt like it became loose 3/4 of the way . Is this normal or have I got a dodgy bolt? I made sure I followed the Haynes manual correctly. I asked a friend of mine and he reckons it's normal as they are strech bolts ?

[tha881]

It depends on your definition of loose. I would say as long as it still took force to tighten and it didnt make any nasty noises it should be okay. I recall mine taking quite a lot of force on the last sequence.

One option is to buy a single head bolt from bmw as they can be replaced singularly, and have a look what's going on if it worries you.