Low cost head gasket replace on '89 525?

[Gene in NC]

Would the Dash01 method be a reasonable risk for head gasket replace on 173k m20 that has no reason to suspect any other head problems like valves?

http://www.bimmernut.com/forum/printthread.php?t=39906

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Post by Dash01. See link above. Thread subject was on 535.

"If it's just the HG itself, that should run ~$50-63, plus ~$3 each for the 14 head bolts, which should be replaced per the one-stretch rule.

The multiple gaskets kit costs ~2X more, though, if you want/need to do more gaskets than just the head. Call BMA for a quote, although your local parts guys can probably get a Reinz or similar kit for the same price, same day and no shipping charges.

To do just the HG and assuming no other work on the head, and that it's straight, should just take a few hours.

It's probably possible to unbolt and raise the head by hoist without removing the wiring harness, if the harness retainer bracket is removed from the firewall to make enough slack in the wire to the computer brain, and/or by unplugging it from the brain. This would entail unbolting the timing chain (at TDC), the exhaust pipes, and the wires to the starter motor, but leaving the intake and exhaust manifolds on the head. A standard hoist or overhead winch should suffice. Raise the head just enough to see and clean the surfaces, so good lighting and mirrors would be helpful.

When putting the head back on, make sure you have both dowel pins in place, to hold the new HG in position: I used old golf club shafts for this, thin and flexible, inserting them through the head and down into the head bolt holes in the block, to guide the head into place as I slowly lowered it to mate with the block."
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Few questions: How to tell if head warped? Assume this approach would work on an m20 in an 89 525?

Effort and cost so low for a DIY job that taking a chance that head is OK seems like a reasonable risk. I've done head gaskets on BMW 2002 and Nissan 4 cylinder so m20 doesn't scare me so much.

[Mordan]

Would the Dash01 method be a reasonable risk for head gasket replace on 173k m20 that has no reason to suspect any other head problems like valves?

http://www.bimmernut.com/forum/printthread.php?t=39906

++++++++++++++++++++
Post by Dash01. See link above. Thread subject was on 535.

"If it's just the HG itself, that should run ~$50-63, plus ~$3 each for the 14 head bolts, which should be replaced per the one-stretch rule.

The multiple gaskets kit costs ~2X more, though, if you want/need to do more gaskets than just the head. Call BMA for a quote, although your local parts guys can probably get a Reinz or similar kit for the same price, same day and no shipping charges.

To do just the HG and assuming no other work on the head, and that it's straight, should just take a few hours.

It's probably possible to unbolt and raise the head by hoist without removing the wiring harness, if the harness retainer bracket is removed from the firewall to make enough slack in the wire to the computer brain, and/or by unplugging it from the brain. This would entail unbolting the timing chain (at TDC), the exhaust pipes, and the wires to the starter motor, but leaving the intake and exhaust manifolds on the head. A standard hoist or overhead winch should suffice. Raise the head just enough to see and clean the surfaces, so good lighting and mirrors would be helpful.

When putting the head back on, make sure you have both dowel pins in place, to hold the new HG in position: I used old golf club shafts for this, thin and flexible, inserting them through the head and down into the head bolt holes in the block, to guide the head into place as I slowly lowered it to mate with the block."
+++++++++++++++++
Few questions: How to tell if head warped? Assume this approach would work on an m20 in an 89 525?

Effort and cost so low for a DIY job that taking a chance that head is OK seems like a reasonable risk. I've done head gaskets on BMW 2002 and Nissan 4 cylinder so m20 doesn't scare me so much.

anyone can elaborate on the one stretch rule for replacing bolts?

as for your issue. do you plan to do it yourself or by a mechanics.. you have to remove the head to tell if the head is warped. You got to measure warpness with feeler gauges.
I did my headgasket but I removed the head. However I can positively say it is possible to hoist the head and put the new head gasket provided you trust the condition of the valves and head surface. why do you want to change the HG?

[Scott C]

anyone can elaborate on the one stretch rule for replacing bolts?

as for your issue. do you plan to do it yourself or by a mechanics.. you have to remove the head to tell if the head is warped. You got to measure warpness with feeler gauges.
I did my headgasket but I removed the head. However I can positively say it is possible to hoist the head and put the new head gasket provided you trust the condition of the valves and head surface. why do you want to change the HG?

The bolts are a one time use (they are torque to yield).

I have done this on the 525i (Vanos). I would not do it again and I consider myself pretty capable. It is a tedious job and that is why it costs so much. If you were to do it, read, read, read. The timing chain guide for one is something to watch out for. You should have 2 people to lift the head off. You can borrow a machinists rule to validate surface straightness.

Make absolutely certain that bolt holes/threads are clean and no fluid is in the block section or you might crack the block due to hydraulic forces of the bolt compressing the fluid

PS - I don't know how you can clean the surfaces adequately without removing the head completely.

Scott

[Ross]

It is foolish not to remove the head all the way, thoroughly clean the gasket surface and inspect it for straightness and cracks have a look at valves, etc.
If you wish to keep the manifolds in place, no big deal, they make a nice handles. Golf club shafts?? Just guide it in place by hand, it's not that heavy.
Use new bolts for sure, following the proper torque sequence and allowing a "rest" before final.

[Bill R.]

hex head bolts on your m20 then you can reuse them, if you have the new style bolts which are torx head then you have to replace them with new.

I also agree with Ross, i'd have the head checked for flatness, cracks and do a valve job on it if needed while its off the car.

[Mordan]

hex head bolts on your m20 then you can reuse them, if you have the new style bolts which are torx head then you have to replace them with new.

I also agree with Ross, i'd have the head checked for flatness, cracks and do a valve job on it if needed while its off the car.

why exactly can't you reuse them? I have been told you can reuse them if some measures are between accepted values.

[Bill R.]

correct, on most OLDER CAR head bolts you can measure the amount stretch and inspect the thread to see if they can be reused or not. On the later m20,m50's and everything newer they have torque to yield bolts which are made to stretch and be somewhat elastic under the torque load, as the head expands and shrinks every time the engine warms up these bolts stretch a little to exert a constant clamping force, When you remove them they contract, if you reinstall they stretch even further before they reach the correct torque/angle. Thats not wanted. So they must be replaced instead of reused if you have torque to yield bolts..... my Dad used to give me the short version of this... he would tell me because i said so.



why exactly can't you reuse them? I have been told you can reuse them if some measures are between accepted values.

[Mordan]

http://www.robbos.com.au/myweb/Tech_Bolts.htm

thx bill R for your response.. I found a page which is quite good.


Unlike a conventional bolt, TTY bolts are tightened beyond their elastic range past their yield point from which the bolt material can recover to its original length, and into the plastic phase of the bolt material. The bolt is permanently stretched and for this reason should not be reused. The reliability of these bolts once stretched is greatly reduced. If they are reused, they are permanently stretched further a second or third time. It is also for this reason why you should never retorque a torque to yield bolt.


Some engine manufactures provide a measurement within which a head bolt may be reused, however the age and history of the bolt is not taken into account. The bolt may well be within specification to pass a simple measurement test but the bolt could be very close to its shear point. Only one failed bolt can result in serious combustion leakage.

has anyone here experienced combustion leakage?

[Ross]

Inadequate clamping of the head gasket can cause it to act like a one way valve, allowing high pressure combustion gasses into the cooling system but still sealing effectively enough to prevent coolant from passing the other direction.
This condition is often mistaken for overheating as the cooling system becomes overpressurized.

[Mordan]

thx Ross.
I think on my old M40 engine (i put another M40 engine), I had a similar one way valve condition. I still have to remove the cylinder head and inspect the head gasket.
but the cooling system was overpressurized and the pressure burst open the radiator who was leaking heaps of water each time the engine was stopped. it was overheating if you didn't add water each time you started the engine.

[bad_manners_god]

When I did the HG on my M50 Non-Vanos I reused the head bolts and torqued them with an impact gun that only goes up to 90 ft/lbs in a center to outward tightening sequence. Worked perfectly fine, no problems.

But defiently take the head out completely, it's easier and faster to clean and you can be much more through.

[Gene in NC]

Thanks to everyone for comments. Mordan raised the question, "Why do you want to do the HG?" I'm going to try to answer the question with a following post and then take that post to open a thread on diagnosing the problem. Short answer is, "HG is the last thing I want to do, but the problem is getting more and more suspicious."

[BigKriss]

how many "stages" (times) did you go over the head bolts to tighten them down properly?


When I did the HG on my M50 Non-Vanos I reused the head bolts and torqued them with an impact gun that only goes up to 90 ft/lbs in a center to outward tightening sequence. Worked perfectly fine, no problems.

But defiently take the head out completely, it's easier and faster to clean and you can be much more through.

[bad_manners_god]

how many "stages" (times) did you go over the head bolts to tighten them down properly?

Well, seated all of them once by hand, then with the impact and did a quarter turn by hand after. Seemed to work fine.