Metric Mechanic 2900 Sport

[jneumss]

because they need to be bored and honed in situ the int bearings probably are a little harder? any machine shop should have equipment to install them

Yeah, that was pretty much it. I have confidence that he'll be able to get it done and I hope to get it back this week sometime.

The oil pump is ruined as well, there was a fair amount of wear/scoring inside, so a new one is on order.

Also, I took the cover off the DME and it turns out I have one that has a stock 2.5l chip that is soldered directly to the main board, so I may search for a different DME and put in a SSSquid Chip until I am ready to put together a MS unit.

[digger]

because they need to be bored and honed in situ the int bearings probably are a little harder? any machine shop should have equipment to install them

standard KS bearings or similar are all you need for mains and rods. for the rings id just get another set of Moly rings for the MM wiseco pistons.

[jneumss]

Not sure on the oil pump yet. I brought it in to a local shop who services lots of e30's and he was going to inspect it for me - I could have done it myself, but I didn't want to take the chance of missing something due to being unfamiliar with it.

The head and the block are at the machine shop - the machinist was a little nervous about installing new intermediate shaft bearings and I am not sure that he has started yet. The bearings are really hard, which surprised me, I thought they would be closer to a regular cam bearing or something, and they came in ~0.020" undersized to the intermediate shaft.

I ordered a Bimmerheads 274 regrind, IE HD rockers, and everything else needed to get the head reassembled, so I can't wait to get that back.

I haven't ordered any of the parts for the bottom end yet. It had standard size coated rod bearings and uncoated main bearings, so I was just planning on replacing with the same thing. I have been researching piston rings. I am leaning towards ordering a set of rings from MM, but open to any recommendations for other moly 86mm rings.

[digger]

it delaminated, would probably cause reduction in pressure. how does the pump look? and the relief valve you want to make sure nothing else is the cause

[jneumss]

The inner bearing had some marking on it, but no damage that I could catch with my fingernail. Also, the shaft is not blocked, I was able to blow some air through it.

Is it possible that the bearing just wore out?

[zaq123]

yes, that bearing is totally destroyed: its outer bearing surface is worn flush with the oil grove in the oil feed hole area. That corresponds perfectly with the area where the seal is pushed out, most likely by the oil pressure. How is the inner bearing? The inner bearing gets lubricated through the shaft itself (if I understand it correctly). Can you blow some air throw the shaft or it's blocked?

[jneumss]

So I took the head into the machine shop and had everything checked out. We pressure checked the valves and the head itself, no warping. The cam journals had some really slight scoring, but nothing we could catch a fingernail on. So it will soon be ready for a new cam, rockers, and rocker shafts, and valve stem seals. Going to do either a 272 or a 274 cam and IE HD rocker arms.

On the bottom end, I took out the pistons, rod bearings had some of their coating worn off but no scoring. Main bearings looked unscathed. Crank overall looked to be in really good shape.

What I did find was that the intermediate shaft seal was pushed out:

And the front bearing was destroyed:

The intermediate shaft itself is in good condition, no markings whatsoever.

So I'm curious if the intermediate shaft bearing failing would be the cause of the lost oil pressure or a result of the losing oil pressure and starving that bearing?

Anybody able to offer any insight on this? I haven't seemed to find anything else internal that would definitively have been the cause.

[digger]

this is how the m20 8.8:1 style piston dome is made

spherical dome (not a hemisphere) approx R100





subtract a spherical dish approx R80mm

the centre of the sphere is offset in two directions from the bore axis (towards the spark plug) as well as being offset in the piston axial direction






section view showing dish (9.7:1 style pistons have bigger radius making a shallower dish)



SO in actual fact the squish is not a chamfer its slightly radiused. Same with the head the machined part is radiused (concave) to match the piston



if you look at the spark plug side the head there is a decent amount of potential area for squish, however the OEM pistons dont utilse much of it because its removed when the dish is added. you could design a custom higher compression set of pistons to use more of the area if you wanted...

[ForcedFirebird]

piston wash due to running rich?

No, sorry for the confusion. The clean spots would be where the squish is correct. If there's a lot of carbon on the squish, that means there is also a lot of combustion going on in there. I find that with a good squish on an m20, the band will be comparatively clean to the rest of the piston - the amount on those pistons, looks like there's far more then optimal clearance between the head/pistons.

[digger]

piston wash due to running rich?

probably water leak

[zaq123]

and how some of the pistons have a really clean spot on the squish band....

piston wash due to running rich?

[digger]

If chamber isn't modified, it looks like there is a barely any squish since the head chamber has very narrow band on the right (pic) and virtually no band near EX/IN piston area. If you look at OEM piston crown and compare it to 885 chamber shape, crown's shape makes sense.
What's CR with those MM pistons? Maybe they are turbo pistons

The head has squish machined in on both sides of the chamber (most of it is in the opposite side to the plug but it is on both sides its easy to see on a clean head). the OEM piston really only uses one side of it because the raised part on the OEM piston is narrow on one side because the offset dish part cuts it largely away. So there could be more potential squish than you first think.

I bought a HG from MM once it was either GOETZE or OE no way they would sell VR

[jneumss]

I also noticed the VR gasket, and how some of the pistons have a really clean spot on the squish band, others are really caked there (as if the squish was inconsistent, like the head was warped).

This engine looks like it had been running overly rich and/or sucking a lot of oil through the valve cover vent.

Does MM really use VR gaskets?

No, I had the head gasket replaced after I bought the car and that's what the local shop put on there. MM has a modified one that they use and that's what was on there before. Chalk it up to me not knowing what head gasket to use and not supplying the shop with a specific one.

[ForcedFirebird]

they are usually 10:1

FWIW when I pulled my head after about 70,000 miles on the MM pistons, they didn't look anywhere near as bad as the ones above.

I also noticed the VR gasket, and how some of the pistons have a really clean spot on the squish band, others are really caked there (as if the squish was inconsistent, like the head was warped).

This engine looks like it had been running overly rich and/or sucking a lot of oil through the valve cover vent.

Does MM really use VR gaskets?

[jneumss]

If chamber isn't modified, it looks like there is a barely any squish since the head chamber has very narrow band on the right (pic) and virtually no band near EX/IN piston area. If you look at OEM piston crown and compare it to 885 chamber shape, crown's shape makes sense.
What's CR with those MM pistons? Maybe they are turbo pistons

They are 10:1.

These had 90k on them over a period 8 years and had the blown head gasket when I bought it. Not sure how much that would contribute to the condition they're in.