M30B28: bore to 89mm

Falkenberg · Post by **Falkenberg** » Wed Dec 14, 2011 12:27 pm

Hi all,

I am the sometimes happy owner of a 1976 E12 528. Last year I have opened the engine because it had a bad knock in the lower end. I found the cylinders to be worn, one even has damage that suggests it had some water in it for some time. I made a quick fix due to lack of time, but next year I would like to get the engine in a better shape. I would like to rebuild rather than swap the whole thing, because the car has matching numbers, and legal things are a bit complicated over here when you change an engine.

Considering several options, I kind of like the idea of boring the cylinders from 86mm to 89mm and fit M30B32 pistons + crankshaft. Would that be possible on a M30B28 block or are the cylinder walls too thin?

labimmer · Post by **labimmer** » Wed Dec 14, 2011 12:41 pm

If you are in Germany, that is understandable, that it is complicated to do the swap.
I did a complete swap since the car 733i had desirable gearbox. https://picasaweb.google.com/109864263698856795064/BMW530iM30B32?authkey=Gv1sRgCMCQzM3Fi4b4AQ#

I also know that B32 is better then B30 US version.
There is no big difference in power but this one runs way better then the original. Much better in Gas
The engine also came with getrag 265 5 speed with overdrive.
Very happy, with the performance.
If I were you I would go for M30B35 Euro,
best regards
lab

On 12/14/11, Falkenberg <bekkerbart@yahoo.co.uk> wrote:

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Hi all,I am the sometimes happy owner of a 1976 E12 528. Last year I have opened the engine because it had a bad knock in the lower end. I found the cylinders to be worn, one even has damage that suggests it had some water in it for some time. I made a quick fix due to lack of time, but next year I would like to get the engine in a better shape. I would like to rebuild rather than swap the whole thing, because the car has matching numbers, and legal things are a bit complicated over here when you change an engine.Considering several options, I kind of like the idea of boring the cylinders from 86mm to 89mm and fit M30B32 pistons + crankshaft. Would that be possible on a M30B28 block or are the cylinder walls too thin?
Malèna: 1976 E12 528
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Falkenberg · Post by **Falkenberg** » Wed Dec 14, 2011 4:23 pm

I don't think I can make a 3.5 out of a 2.8? The leap from 86mm to 92mm is not possible, I think..?
So I would settle for 3.2, if possible.

labimmer · Post by **labimmer** » Wed Dec 14, 2011 7:12 pm

I was thinking to swap the hole engine, since M30B34 in late 70`s early 80`s had 218PS

From: Falkenberg [mailto:bekkerbart@yahoo.co.uk]
Sent: Wednesday, December 14, 2011 5:23 PM
To: tech_forum@firstfives.org
Subject: Re: M30B28: bore to 89mm

I don't think I can make a 3.5 out of a 2.8? The leap from 86mm to 92mm is not possible, I think..?
So I would settle for 3.2, if possible.

Malèna: 1976 E12 528

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Sent using Mail2Forum (http://www.mail2forum.com).

Read this topic online here:
http://www.firstfives.org/bboard/viewtopic.php?p=13235#13235

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Mike W. · Post by **Mike W.** » Wed Dec 14, 2011 9:18 pm

You should be able to bore it from 86 to 89, I've heard of it being done, and I personally have taken a 89 bore to 92MM. It was thin, but it worked, when I sold it I had put 175K miles on that engine since I rebuilt it. You can't go from 86 to 92, that is way too far. As far as putting in a 86MM crankshaft, it's maybe. If the engine has small bulges on the lower crankcase, you probably can, but 76 is not likely, you can probably only go to 3.0 They widened the crankcase some to allow longer throw cranks, we got the 3.0 in early E12s, and the very early ones were labeled on the side of the block, 3.0. Later ones which would take the longer throw crank were labeled 3.0/3.3. If you need help finding the bulges, it would be at least until the weekend before I could take a pic. I've got lots of engine pictures, but all of the top. The head, the pistons, but none of the lower block.

Falkenberg · Post by **Falkenberg** » Thu Dec 15, 2011 4:09 am

Mike W. wrote:You should be able to bore it from 86 to 89, I've heard of it being done

That is good news.

Mike W. wrote:As far as putting in a 86MM crankshaft, it's maybe. If the engine has small bulges on the lower crankcase, you probably can, but 76 is not likely, you can probably only go to 3.0

That is bad news. Some pictures of those bulges would be very helpful, there is no hurry. I even might have some time this weekend to give it a try with a spare '77 2.8 block and a 3.5 crank that I have laying around..

Falkenberg · Post by **Falkenberg** » Mon Jan 09, 2012 4:14 am

So I had some time last weekend, and I tried to place the camshaft that should be from a 3.5 in am old 2.8 engine block.
I was able to fit it and turn it around, with one M30B28 piston and conrod connected to it.

The problem is that I was expecting for the piston to pop out of the block at TDC, but it aligns fine with the block. Which makes me suspect that I actually bought just another 80mm camshaft and not a 86mm.

Is there any way that I can measure the camshaft with basic tools?

Mike W. · Post by **Mike W.** » Wed Jan 11, 2012 9:39 pm

There is, I've done it, but now I'm trying to remember how. And I was trying to confirm I had a 84MM M5 crankshaft. If you have it in the block, just measure the difference between top and bottom. Actually that's easiest with the piston in as you had it. Do that with a caliper and you will get the stroke. You could even use a metal rule or a tape measure with somewhat less accuracy, but probably enough. But I did it with the crank on the garage floor, Hmmm, how did I do it? I'll have to think on that one, but I also need to take a pic of the bulges I'm talking about.

Falkenberg · Post by **Falkenberg** » Sat Jan 14, 2012 9:42 am

I measured the crankshaft today, it's an 80mm, as I suspected. So I have to find a real 86mm.

Falkenberg · Post by **Falkenberg** » Mon Jan 16, 2012 3:39 am

Mike W. wrote:.. bulges ..

I just was looking at a picture of an M30 block:

The lower vertical 'bulges' are the ones you are referring to?

DEMIURGE · Post by **DEMIURGE** » Mon Jan 16, 2012 1:06 pm

We have discussed this topic maybe two or three years ago.
I've posted the same topic at the MyE28 forum.
Some of the forum members were of the opinion, that it is possible to bore the cylinder walls from 86 to 89 mm. Some of them even did this. With no doubt - the engines ran and maybe are running now, but all of these engines are used without any serious abuse - just for daily driving.
I wanted to do the same bore job for my b25/28 block.
But I gave up...
This happened, when I measured the wall thickness.
My measure wasn't so technical or scientific, but it showed something around 6mm. When you bore the cylinders to 89 mm - the cylinder wall thickness will be something around 4.5mm or less. There is no guarantee to follow the the original cylinder axis.
With no doubt - the other arising problem is the engine cooling.
I'm not speaking about changing the radiator or the pump to get better flow. When the temperature rises - there is real danger of forming little bubbles around the walls (from the inside). This process will make worse the cooling of the block. The thinner walls will worse dissipate the heat to the lower part of the block and so on.

So, the decision is only yours.
The best way is to switch to a M30B35 from e34/e32. There are a lot of these engines in Germany. I chose this way.

Falkenberg · Post by **Falkenberg** » Tue Jan 17, 2012 4:14 am

Hi Alexander, thanks for your detailed reply.

I am not looking to turn my car in to a race car, I just really want to keep the original engine.

Just curiosity, how did you manage to fit the E32/E34 block? They have different engine mounts as far as I know. I might fit one of those just until I get the original engine running well again.

ps. we are neighbours

I'm living on the other side of the Danube.

DEMIURGE · Post by **DEMIURGE** » Tue Jan 17, 2012 5:51 am

I didn't fit yet the e32 M30B35 engine in my second e12.
Yes, you are right - the engine mounts are different. Here in the forum you can find the needed information. Also you can browse the MyE28 forum. There you can find similar topics with good explanations and pictures. Some of the FirstFive forum members went through this conversion. It isn't so difficult - even some of the holes in the block coincide. You can extend the existing mounts, or make a new ones, or mount on the existing block holes a piece of strong enough V-shaped steel (elbow) and then mount the block on them...

The Euro M30B28 engine is good enough for daily driving. I use an e28 head and all the needed "periphery" with L-jetronic engine management on my first e12. Of course Motronic is better and it is possible to fit it on this engine, preferably 1.3 version or even you can think of MS management or something similar.

Falkenberg · Post by **Falkenberg** » Tue Jan 17, 2012 6:29 am

I have the 2.8 version with zenith carburetors, 165hp but the cylinders are badly worn.

I might have the luck of finding an E23 or E28 engine, but in the end I would like to repair the existing engine.

I 'played' a bit with MS on my old E32, it sure is nice stuff.

DEMIURGE · Post by **DEMIURGE** » Tue Jan 17, 2012 8:03 am

I also had Zenith Inat carburettors on my first e12.
It was a real "drama" to synchronize them. You know - there are "only" seven adjustment screws. In my case, after a proper adjustment, everytime they gone loose in some way - fixing the screws didn't help. Three of the cylinders were always overriched, the others went lean. The fuel consumption was over 20 liters at 100 km... That was the reason to switch to L-Jetronic.
Of course, I used my original '76 block.

There are three ways to use your worn block.
1. If the the block is not so BADLY worn - just make a new honing and use a special oversized piston rings with the original pistons. It is possible to find them. I've bought such rings for my M30B35 block from Walloth&Nesch.
2. Get the next suitable size pistons and rings. You can buy oversized piston from ebay for example (second hand) and buy new rings.
3. You can rebore your block and than fit an original size mantle or jacket - I don't know the right term in English. Every mantle is bored to fix properly to the corresponded piston. Then you can't mix them. If it is necessary - you'll adjust the rings gap. It is not a job for IT specialist (for me also - I'm an electronic engineer) - you have to leave it to a professionals...

Of course - the fourth way is to bore to 89 mm