Should i fit uprated mains and bigend shells?

[appletree]

Right got the final big bits to order for my engine build ready for when it comes end of october.

Thing is when it comes to shells theres a few options...

One of the weak spots with the M42 engine is the fact that it only has a 180* thrust bearing surface, there is a way to get round this how ever it requires some machining work which i could do but...

So theres some options

Option 1 - Fit standard mains and rods and have the posobilty of running some oil with a stronger film stregnth but the 180* thrust surface would be retained.

Option 2 - Fit some 325 ones with a 360* thrust bearing but i'd have to machine a new tang in the main cap this would also give a 360* oil groove but there standard shells not uprated.

The above could be used with standard big end shells

Option 3 - or with trimetal bigend shells

Option 4 - Fit some upgraded mains and big ends with low friction high temp coating but only a 180* thrust bearing

[Jhonno]

Low friction? Helps the oil glide nicely over them.... Bearing (I'll get my coat) in mind, there should be no metal to metal contact!!

[appletree]

Sorry wrong turm, not a thrust bearing a thrust surface on the shell to stop end float.

If people would be willing to add why the voted what they did that would be good to.

[DanThe]

If you have a supercharger hanging off the end of the crank 360° of thrust bearing would be a very good idea

[baptie0]

i would go for the 360* bearings to cope with the extra thrust & standard shells.

[irish320i]

I think if you can go with the 360 degree with machining that you can do yourself it should improve the life of them considerably

[GeoffBob]

360' degree thrust bearing with uprated main and bigends. Check bearing clearance with plastigage. Oh, and since your crank is foreign to your engine (M47, as I recall?) maybe an alignment hone is in order. I'd personally suggest blueprinting your engine as you go along, purely for the peace of mind, satisfaction, and enjoyment of doing it - a blueprinted engine is a very special thing. But then I'm anally retentive when it come to building engines and blueprinting is certainly not a requirement in order to deliver a working engine to your engine bay.

Glad to hear its all coming together Matt, well done! Remind me again what CR and pistons you have opted for please.

[appletree]

I decided to keep the standard crank as the m47 one would idealy need longer conrods which would mean even shallower piston which could mean they would 'rock' down the bore, don't know the technical turm.

The compression ratio is 8.5:1

Would like the 360' thrust surface my self but need to look at the machining to get them to fit.

[GeoffBob]

Ah yes, rings a bell. I seem to recall reading your thread where you investigated the whole M47 crank issue. Included something to do with a Rover engine if I am not mistaken??

8.5:1 CR sounds most excellent.

Should be possible to have a machine shop mill that extra tang without too much hassle, or do it yourself if you have the equipment.

[appletree]

I could machine the extra tang in easy enough in the cap but the other half thats cast in to the block may be alittle more difficult and the other thing i need to look at is how the half of the thats in the block is machined as standard as the shell is just to say narrower than the cap and sits in a recess on the thrust surface but i doubt the top would be the same or why would bmw have just fitted a 180* shell

Pics may help people understand so follow the link bellow and look at page 10.

http://www.metricmechanic.com/pdfs/metr ... ooklet.pdf

[appletree]

Small update, just bin outside and stripped a fubared M42 i had laying around to see what the set up was.

Result the groove/recess one the cap is on booth halfs so i just need to machine a new tang in it, few pics

Totaly shagged shell oil was black with white metal in it

[GeoffBob]

Interesting document that Matt! never seen it before, have added it to my collection. Sure seems that there is a lot of worthwhile upgrades that you could do to your M42.

I should emphasise that anything you do to lower your internal friction (with improved bearings etc) will help lower the "work" (in Joules) that your engine puts into heating your oil and water, and the less work your engine does against friction the more is available at the flywheel. To a very, very rough approximation a bog standard 4-pot will spend around 45 Joules of energy on every rotation of the crank. This figure is purely energy lost to frictional heating, it does not include energy deposited/stored in the inertia of the crank, flywheel etc.

That 45J per rotation equates to 0.75 watts of power per RPM. That is to say, at 6000RPM its costing you roughly 4.5kW (about 4 electric kettles) in work done against friction just to keep your engine turning (which is partly why engines overheat so damn quick with inadequate cooling). Anything you can do to reduce your frictional losses will be to your advantage.

I'd certainly recommend that, at the very least, you fit tri-metal bearings. I have no experience with the Teflon coated (low friction) versions. It sounds to me like they would require regular replacement to maintain their advantage as I suspect that the Teflon coating is quick to disappear, but I could be wrong.

[Jon_Bmw]

That is not shagged matt, you should see some I took out of a mates mi16 that had spun!

[appletree]

lol well these shells arnt exactly brilliant, looks as though the sump may have had an argument with a kurb and lost! so its probably ran with no oil in for a bit, until some ruff c**t filled the hole up with liquid metal! not a pritty sight.

This area should be flat.



Good news is ive managed to get the other half of the shell out with the thrust surface on and it fits the cap half perfect minus the tang so it is just the tang slot in the cap that needs to be modded which i can do easy peasy

Not a happy shell