enlarging bore m30b30

[budgerian]

One more question: Shouldn't the 3.0/3.3 castings always have the reliefs around the crank area, since the 3.3 uses the same 86mm crank as the 3.5?

Thinking along, would a 3.0 benefit from putting the 3.5 crank in, effectively making it a 3.3?

The 3.3 was never available with D-jetronic. I wonder how this would change the engines characteristics. I assume it would rev slower but have more torque.
The E3 3.3's were less powerful (but had more torque) than the 3.0Si's but I always thought this was due to lower compression and carbs (or in case of the 3.3Li more restrictive L-jetronic)vs fi.

Anybody ever done this or has thoughts to share?

 

[roundel]

M30

Marc,
They were using special blocks without waterways between the cylinders. As I understand they were very concerned that the water system would not work properly like this. But as we know it was Ok & a few years later the production 635 used this system.
Also we should consider that any engine block you find now has 30-40 years of internal corrosion to take into account. The cylinder wall thickness of 3mm then could easily be only 2mm now.
Alex

 

[budgerian]

Finally got around to pulling the sump today, and was
able to answer my own question for good, but here's for future reference:
Although the casting says 3.0/3.3, there are no notches in the inner casting to make room for an 86mm crank and the cilinder jackets do indeed have passages inbetween them.
Some crude measuring showed that jacket thickness is about 5mm, which seems to thin to bore up to 92 mm.

Checked on a REAL 3.3 block and established that these can indeed be bored out to 92mm (no passages between the jackets) and they have the notches for the 86mm crank.

So there you have it, or rather: I don't..

 

[lloyd]

Mahle pistons are great but darned expensive, I have used pistons for Toyota pickups with the R22 engine, they have a big compression bump on top that can be machined off to give you the compression ratio that you want, plus they were a little lighter and a whole lot cheaper. . . . They can be purchased only in sets of 4 from Silvalite and they are also available in oversizes. Piston pin size is the same as BMW. Good luck, Leroy

Interesting. I have a long gone friend who claimed he substituted Mahle pistons originally designated for a VW Beetle with little or no machining into his Toyota, just because he had them sitting on the shelf. He claimed he had thought about using them in a 1600 or 2002 project. I just read another thread on this forum where a Nissan pickup may also be a suitable piston candidate.

Regarding the R22 pistons, we all know that any reduction of reciprocating mass is generally a good thing, but since you mention "lighter" and "machining," are you still factoring in a total dynamic balance with the crank (and possibly the harmonic balancer and flywheel)? I ask only because some of the savings may be offset by the machine shop's balancing charges. While on the subject of pistons, what rings did you use, as often (not always) pistons are sold with rings.

TIA

 

[M5dCS]

pistons and rings

It's been a few years ( about 6 or 7 ) since I built a 3.5 for a friend, but I think my cost for a set of 4 pistons was about $45. The rings I used were Perfect Circle for the toyota R22 application. I use cast iron rins because they seat quickly and if there is ever a catastrophic engine problem, they don't destroy the cylinder walls. I'm a firm believer in engine balance, all pistons need to be within 1 gram or less of differance and all connecting rods need to be within a gram on both small and big ends. That being said and without getting too far into engine dynamics, an inline engine like a BMW 4 or 6 cylinder usually has a very spot on crankshaft balance and therefore you can do a piston and connecting rod balance and have an engine that will be better than factory balance, but if you are going to spin the engine above about 6500rpm, I would spend the money regardless and have a complete engine balance done, it just makes good sense. I used to work on gas turbine that spun at 42,500rpm, so yes I'm sticky on correct balance, and yes it does pay off on engine life. Good luck with your project, and call me if you have questions.
Leroy Braden 208-347-3309

 

[Markos]

I’m bumping this thread back from the dead. There is some really good info in here that I would love to validate. I’ve long since written off any boring or stroking of my 2.8 motor. I’m not unhappy with it anyway.

However, new member @M-tuner mentioned that he was building 3.5’s out of the 3.0s in the 80’s. I would love to get some clarification on that, knowing that the 3.5 m90 came on the market in ‘78. Was this an overbored 3.0 motor from a CS? If so, how long did it last before blowing a cylinder wall? If it was stroked, how did you handle the connecting rod clearance.

This has no application for what I am interested in, I just love learning more about these motors, particularly from folks who have been at it for 30 years.

Just reading about m30 blocks on this site lots of miss info I was building 3.5 out of 3.0 cs s and Bavaria’s in 1980s I did a Bavaria that out ran a 1972 911s the guy raced me twice from a red light to get his ass handed to him doing a lot of research on m49 and 2 valve race motors, Josef schnitzer designed all the modern m motors m88 s38 s14 just look at the schnitzer formula 2 a 2 piece head not one piece as the m49 and every one above him took credit. Bruce m tuner

 

[M-tuner]

there is the 2/5/ 2/8 block the 3.0/ 3/3 block the 3/3 3/5 block and the 3.5 block and then the s38 block any over bore starts first clean and bake block ck for cracks, sonic ck bores, the 3.0 / 3,3 block can go to 92 mm if checked for core shift, the 3/3 3.5 block is simmesed it has steam holes at the bore intersection, can be bored 94mm , the 3.5 can be bored the same as m90 m106 m88 or s38 its the same block, it can be bored 95mm , the m88 and s38 have a modified oil return tube, which can be added to a 3.5 block, the m102 and m106 have a oil return tube for the turbo, the e34 e38 and s38 had a spring loaded oil chain tensioner. some blocks were marked 3.0 /3.2 3.2 /3.4 the m90 block was a m88 m1 block simmised bores withe no oil return tube for the 4 valve head. it can be built to 3.7 3658 this can vary depending on head and head gasket volume which is actual volume not tax volume which is bore x stroke. the m90 did not share the 3.0 design it was the result of m49 development 94 x 84mm race engine for the csl 4 valve 430 hp engine which was redesigned by Joesph Schnitzer from a laydown to a upright m88 2 piece head ,M1 I have never had a 6 blow any head gasket, if you over heat them the gasket gets compressed, and you loose the head bolt tension block to head. the later blocks had clearance for the rod bolts , I specialize in bored and stroked m10 and m30 ,s38 my last motor was 92x88 m10 316 schrick, 45 doe s webers 230 -240 hp street 2002. I have built 95x 90 s38 400hp I am building a 95x86mm, 3.7 m106 745i turbo @ 500 to the ground @ 1 bar Bruce M tuner

 

[Markos]

Thanks for checking in Bruce!