Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Cracked head bolt holes in BMW M20 Block - Between 2 water jackets


I am on a budget and CANNOT replace the block. Repeat, Cannot. I simply do not have the funds, time or space.

Now, that being said. I have a 323i E21 BMW 1982 with a stock Bmw m20 engine. I just installed a “new” engine in the car because the old one was toast. The new one had some white smoke issues so i pulled the head gasket only to find the head bolt holes in the block were cracked between two water jackets. (5 holes were like this.) No cracks lead to cylinders nor even in their direction

Now im going to install the revalved head with the new head gasket no matter what. However, I want to know what are the issues I should be expecting SPECIFICALLY(Please dont just tell me it just wont work).

I am thinking I will have torqueing issues on the head bolts so im thinking Im going to compensate by using a teflon liquid on the bolts going in to the ones with the cracks, and just oil on the ones with no cracks.

Constructive thoughts and observations would be appreciated.

Love the show - thanks for you time.


So you have to use the sealant on the head bolts which may even be recommended. Try heatproof RTV type sealant if none is recommended. It’s like the regular stuff for any old gasket. If you have those spiral head bolts, seal them all the way up the shank. Get a radiator cap rated for 7 PSI. Pray once and have faith. Seal any head bolts all the way up for that matter.

Money pit…Divorce it. It’s not worth it…A 1982 ANYTHING is simply not worth it…

You will not get Tom and Ray on this forum; only an assortment of DIYers and pro techs who try to help by offering advice.

Bluntly, I think this new engine has some serious issues and liquid Teflon is not going to accomplish much in regards to sealing a crack or improving the bolt torque capabilities. Liquid Teflon can help on sealing something like pipe fittings and A/C fittings but I wouldn’t use it on anything else.

White smoke, blown head gasket, cracked head bolts into the water jacket would tell me this engine was so overheated that it was probably glowing in the dark.
If this is the case you can probably assume the cylinder walls and piston rings are junk; and it could very well have lower end problems also due to washed out crankshaft bearings and journals.

Since you’ve had the head redone and have a gasket set already about all you can do is put it back together, head to the closest church for a short time, and then head back home to fire it up and see what happens.

What about the block in your “toast” engine? Is the block “toast”? As to the DIYers and pro tech comment from ok4450…I am a mechanic. Automotive and diesel. I’m sure there are a lot of other mechanics who post answers here also. I see a lot of good advice here that DIYers and pro techs would know nothing about.

Is this a grey market car? I didn’t think they sold the 323i in the US. Either way, you should also be posting this question on BMW enthusiast’s sites (Great Britain, also), you might find someone that had this exact situation.

Those cracks are a fairly common M20 problem. Either that engine has been overheated or its had a head job at some point and the bolt holes weren’t cleaned out correctly before head installation - if oil/water isn’t cleaned out of the bolt holes, the hydraulic pressure trapped by the bolt will crack the block.

You not only have the likelihood of a water leak but the bolts probably won’t torque down correctly and may strip the block threads, then you’ll need to use Timeserts (don’t use Helicoil on the M20 block).

In brief that cracked block is junk, you really need to go and find another one, fitting that head gasket will be a total waste of time. I know you’re on a budget but M20s are plentiful and cheap.

Try one of the Bimmer forums parts sections.

I wonder if you could get the best, strongest, most heat-resistant epoxy you can find, thoroughly clean the block, apply it, and drill & tap the holes?

Aside from that, is there any kind of warranty on the ‘new’ engine? If you got it used, most places will warrant it to not “knock, smoke, or have a cracked block”

In engineering terms, cracks are fatigue failures in the middle of the failure. They are stress concentraters. The cracks are going to grow every time the block goes through a heat cycle.

Current crack propagation theory says that cracks store up energy and grow very slowly, then they will reach a threshold where they will release the energy all at once - meaning the crack will grow suddenly - and the growth will be much larger than the current crack size.

You can see this in windshields that have a tiny stone chip, which will grow into a crack - and every time the crack grows, the new length is more than twice the length of the old one.

If the crack in your block goes through the water jacket, it is possible that the next growth cycle will be into the cylinder wall.

So while you may not want to hear that the block is trash - because of economics - it would not be good economic planning to continue to use the old block - you are going to need to replace fairly soon - and at a time and a place where the engine block chooses, and Murphy’s Law says this will be very inconvenient and maybe even dangerous.

The key to all this is the quotation marks around the word new. This is not a new engine block, where did you get it and why do you think, despite what all these pros and highly expert mechanics have to say that you can get away with spit and prayer when what you need as a block that is not cracked? How far is it to your job, school? A bike is cheeper than a new block. Or take the bus. Or as a last resort, make a friend, and ride with her. Teflon will change the torque values radically by the way, and then the head gasket will blow again, and so on…