Head Bolts?

[Dre0415]

Hey Guys, You may have seen one of my other posts already im currently in the process of putting my 1997 BMW Z3 back together and I already ordered a ton of parts for it. Anyways my main question is about the head bolts. I already ordered the M10x95mm head bolts and from what I can see they look to fit perfectly fine I stuck one of them through the head to see how far it would stick out and it sticks out a solid 2-3inches which is more then enough to reach the first few threads of the block. But after doing some more research people are saying that I need M10x110mm so the bolt is 15mm longer. Do I really need to get the longer bolts or should 95mm work perfectly fine. I cant seem to find a defintive answer because the 95mm bolts were also used on the M52 and S52 at one point in time and the S52s head is exactly the same as the M52 the only differences are cams. I did check realoem and it seems that I probably should have gotten the 110mm ones instead. Does anyone know if it actually matters? The main reason I got the 95mm is because I saw someone else on a different forum who said the bolts he received were too long and id personally would rather have them short and still be able to work and not too long and not able to be used.

Thanks for the help,
Dre

 

[NZ00Z3]

A few dumb questions, as I'm not sure why you have pulled the engine apart compared to just putting a second hand engine in (usually cheaper than a full gasket set):

• Are you working with an aluminum Z3 M52TUB28 engine? Most of the M52TUB28's in the USA are iron blocks.
• Are you going forced induction on the engine? Looking for extra loads on the bolts.
• If it is an aluminum block, was it over heated? Most times the cooling system fails, engine over heats, aluminum parts warp and head gasket blows.
• If it is an over heated Aluminum block, have you had the block hardness tested? This checks to see that the aluminum is still strong enough to hold the head bolts in place without stripping.

For forced induction, find an iron block engine. It just stays in one piece a lot longer and you can run higher boost. If its a boosted aluminum block, Timesert (not Helicoil) the head bolt holes in the bock. If you don't do it the first time, you'll do it the second time. This is an exacting job as you want the insert to be straight and true, so a jig is needed. Do a search on the job for tips.

If its an over heated aluminum block, you want the most amount of thread on the head bolts that you can get.

If its a soft (bad hardness test) aluminum block, then you need to Timesert (not helicoil) the head bolt holes.

If it's an aluminium block and you're not sure if it's been over heated and have not done a hardness test? You way up the risks and costs of having to pull the engine apart a second time and timesert the head bolt holes compared to getting away without doing the timesert job.

 

[Dre0415]

Hi, thanks for your reply I'm not doing any power adding modifications. The reason I pulled off the head off is because the bolt that holds the upper timing chain tensioner snapped on me. When I was installing new lifters. This bolt is just about impossible to extract without removing the head. So that's what I'm doing. My engine code is M52B28 it is not the technical upgrade model as it only comes with single vanos. I guess from my understanding the m52b28s came with an aluminum block and a cast iron block and I'm not sure which one I have. Next week I am bringing the head to a machine shop to get it cleaned and I will have them check for warpage but for as long as I've had it. It has never over heated. From what I'm reading online though the z3s m52 only came with the aluminum block.

Also the reason I am repairing this block instead if swapping it is one because these m52s aren't that easy to find atleast where I've been looking and they usually run about $1200 the cost to repair this block is only going to cost me about $200

 

[AirOps]

The M52B28 in 1997 & early 1998 in the Z3's had Aluminum blocks, in late 98 the blocks were switched to iron like the rest of the 6 cylinder BMW's in the US. The "stated" problem was that the the high level of sulfur in the US gasoline was affecting the nickasil coating on the cylinder bores. Some engines were replaced by BMW with iron blocks, a magnet would be quickest way to determine which material your block is made with.

 

[Dre0415]

That's some very useful information. I will check once I'm back home with a magnet to see whether it's aluminum or not. Either way i went ahead and ordered the 110mm headbolts as the bolts as the original head bolts were definitely 110mm. It's very unfortunate that alot of these websites cannot decipher parts differences even when you give them all the info about your car. They sent me a head gasket a m52tu even though the tu didn't exist until 1998. It's a pain to get parts for this engine because of all the changes bmw made in such a short amount of time.

 

[Mike Fishwick]

All you need to do is look at the block - aluminium is silver coloured . . .

 

[Dre0415]

I can confirm my block is aluminum. Which would make sense why the head bolts are longer because aluminum is weaker then cast iron. I was a little bummed out because honestly I would personally like a stronger cast iron block but it is good to know that my engine is significantly lighter then what some other people have. Either way this engine still looks brand new from the inside.

 

[Delk]

The aluminum block is plenty strong enough. I had to put inserts in mine along with ARP head studs but thats because it now has a big turbo strapped to it and puts out over 400hp.

The iron block maybe stronger but you have to really need it to make up for the extra weight.