135mm conrods engine build ideas, rainy day............

[Simon13]

Bit bored with the rain and i've always meant to do this, nothing ground breaking but in my passage are this lot




4 different types of 135mm conrods from the left,

M20 - 2.5

M50 - 2.5

M52 - 2.8

Alpina B3s or B5 engine - 3.35


And on the scales




M20




M50




M52





Alpina, these rods are also used on the earlier 3.3 engine fitted to e39 and e46's but its still a 135mm length rod


I've not got or know whether any M54 conrods apply i'm afraid or any newer N52 or N53 engine stuff. We will have to wait another 10 years!

I've weighed them all the same as the engine builders do when they balance your bottom end, with the rod bolts fitted but no big end shells



All it shows is you can get some real weight loss off the bottom end parts just using low cost BMW parts bin. I'm not sure how much weigh custom controds would weigh. So if you rebuilding your M20 or whatever this wouldn't be a bad bet

I'd also use the M52 2.5 crank and lighter flywheel on your M20 2.5 rebuild and you could save 7kgs odd off the bottom end. Transform they way it performs drives even with a stock camshaft fitted

[ross_jsy]

Interesting information. I'll be buying some Eagle H beam rods in the near future so I shall weigh those

[reggid]

I cant see the pics on this PC but i currently use a Metric Mechanic set of ultralite aftermarket I-Beam rods in 138 mm length which are 475g. these are not available in 135 mm length though these also use a 1mm smaller pin (21mm) like the Alpina 3.3 engines to allow a better ring design.

Molnar rods have a 135mm H-Beam rod design that is 484g

[jimbom30cab]

Interesting stuff there, might have a chat with you Si about building a lightweight m20, could be great fun to drive.

[Simon13]

I cant see the pics on this PC but i currently use a Metric Mechanic set of ultralite aftermarket I-Beam rods in 138 mm length which are 475g. these are not available in 135 mm length though these also use a 1mm smaller pin (21mm) like the Alpina 3.3 engines to allow a better ring design.

Molnar rods have a 135mm H-Beam rod design that is 484g

they'll cost a bit more than the £40 most folk want for these worthless rods eh?

[reggid]

was just an FYI as to how light they get, a fair bit harder to find rods downunder though so it is very common to use aftermarket rods around here. some are way overboard in terms of $$$.
nevertheless i do have a set of 3.3/3.4L rods amongst other things from the same bottom end for a "rainy day"

[Simon13]

true shows you how light decent aftermarket rods weigh plus some lighter pistons and it all really adds up

[reggid]

lightweight stuff is a must if you want to spin more than stock rpm and retain nearly stock longevity.
if all you want is lightweight stuff without opening her up a lightened fly does a similar job but obviously you can only go so far with lightening a fly (12lb?) and you will probably only notice the difference of a lightened fly in 1st and 2nd as the effect/perception diminishes quickly when changing to the higher gears

[Demlotcrew]

Holly smokes! The factory parts are lighter than after market race gear!!!

[reggid]

Holly smokes! The factory parts are lighter than after market race gear!!!

what does the factory S14 stuff weigh?

data i have said rod, piston , pin is 1270g for 2.3L

[DanThe]

IIRC the M20 piston is over 600g

[reggid]

m20b25 piston is 385g (short skirt version)
S14b23 piston is 475g (it is a much bigger bore that is why it is heavier)

this exludes pin and rings

[DanThe]

Close then

[Demlotcrew]

Weighed a rod on its own. Not exactly accurate scales, but they do offer a guide.

This is not a stock 2.3l rod, its much longer.

[reggid]

whats the S14 deck height?

[tim_s]

M54 has 135 rods too, are similar to m52 ones and are cracked which I think is worth having. I put these on an m42 I built once.

[Demlotcrew]

whats the S14 deck height?

The extra length comes from the design of the piston and smaller pin.

Notice how high the pin sits on the piston. I will post a stock comparison this evening.

[DanThe]

M54 has 135 rods too, are similar to m52 ones and are cracked which I think is worth having. I put these on an m42 I built once.

Same part as M52 Tim, not cracked though

http://www.realoem.com/bmw/partxref.do? ... showeur=on

[reggid]

whats the S14 deck height?

The extra length comes from the design of the piston and smaller pin.

Notice how high the pin sits on the piston. I will post a stock comparison this evening.

yeah mine are only 23.5mm comp height IIRC and cut into the oil ring. the deck height on m20 is only circa 206mm so cant use long rods when you throw some extra crank in. you could fit a 144 rod in a M20B25 with custom piston.

arent you using the 94mm crank to? with those rods assuming near 150mm must have 22X deck height atleast to fit it in

[tim_s]

M54 has 135 rods too, are similar to m52 ones and are cracked which I think is worth having. I put these on an m42 I built once.

Same part as M52 Tim, not cracked though

http://www.realoem.com/bmw/partxref.do? ... showeur=on

Ah, yeah, I stand corrected, now that you've linked that I recall it was the m44 140mm rods that are cracked and the m54 ones not.

[reggid]

m20b25 mahle (big skirts) 9.7:1 84.5mm (+0.5mm) piston is

bare piston 411g
piston pin 105g
rings 28g
TOTAL 544g