Piston + Valve: How Much Damage Is Too Much?

[Exodus_2pt0]

Compressed air will get most debri out of there after your done. It's the stuff that settles down between the cylinder wall and ring land that you gotta worry about.

[FLG]

Might want to steer MM to this thread that has been going on, on the charger forum im a part of.

http://www.dodgecharger.com/forum/index.php/topic,46015.0.html

Some VERY good info and some private testing was done as well. Its a bit to read through but covers what oil is high zinc and safe to use.

[bmwman91]

Thanks for the link. Very informative.

From searching around, it looks like Mobil 1 15W-50 synthetic is the way to go from here on, which happens to be what I have always run. High ZDDP levels for flat tappet applications.

http://www.mobil.com/USA-English/MotorOil/Files/Mobil_1_Product_Guide.pdf

I had cheap-o Pennzoil 10W-40 in there. MM recommends cheap detergent dino oil for the first 50 miles, change it, and then more of it for the next 500-1000 miles (I was just over 1000 miles and planning to put the M1 in). Thereafter they recommend Mobil 1 15W-50. When I talk to them tomorrow I will pass on the link and let them know that they may want to consider recommending a ZDDP additive with the break-in oil.

[FLG]

Yep,

For break in with my 440 the guys at the dyno swear by Joe Gibbs break in oil, id use that for break in then the other line of Gibbs oil there after.

[AndrewBird]

Piston rings well either have a small pin to locate them so they don't spin, or they won't and will spin when the engine is running (not sure how an m20 is). Either way, you don't have to worry about the rings moving.

[Ryann]

I would definitely pull that piston and mic the top ring land. Valve contact is close enough to the edge that it could be slightly pinched.

[bmwman91]

Piston rings well either have a small pin to locate them so they don't spin, or they won't and will spin when the engine is running (not sure how an m20 is). Either way, you don't have to worry about the rings moving.

Good to know, thanks.

This is a M42 engine, just for clarification. Yeah I know, who the heck would pay the MM premium for an M42 lol. Holy shit did this thing move before the valve spring crapped out though!

I would definitely pull that piston and mic the top ring land. Valve contact is close enough to the edge that it could be slightly pinched.

Aah ok, so the issue is that the ring land could be constricted and pinching down on the ring...that makes sense. I will ask MM about the land depth and stuff tomorrow so that I can get an idea of what I am looking for.

[blueapplesoda]

Most bmw pistons allow the rings to spin free (all of the bmw engines I have seen), as long as you don't replace the rings, you don't have to hone the cylinder and you can put the rings back, like nitro said. I usually try to index them when they come out so I can place them accordingly when they go back together.

[bmwman91]

Question...where is the oil check valve that sits between the head & block? I did not see anything like that when I pulled the head. I did not look super hard or anything either, but nothing stood out.

Part 9 is what I am asking about...where is the little bugger?

http://www.realoem.com/bmw/showparts.do?model=AF93&mospid=47305&btnr=11_4380&hg=11&fg=10

[MF DOOM]

I think those were in the later m42s.. Im not positive but i remember reading something about that in one of rob_e30's threads for his m42 turbo track car. ill do a quick search

EDIT: Found the thread. Same part?

[bmwman91]

Yeah, turns out that the check valve only applies to 93+ M42's. You would have to machine the block to accept it on the early/E30 M42 engines.

[spdracrm3]

]

Piston rings well either have a small pin to locate them so they don't spin, or they won't and will spin when the engine is running (not sure how an m20 is). Either way, you don't have to worry about the rings moving.

this is only on 2 stroke engines where ring ends could end up in the side ports and break off. four stroke engines dont pin their rings and they do move all the time,and are not intended to stay put in the lands . the break in is to make the outer surface of the rings conform to the shape of the bore ,but the bores are so good and ring quality is so good now they really dont need a break in nowdays.so dont worry about ring position as they wont be where they were when installed anyway.just space them in thirds around the piston on install

I would definitely pull that piston and mic the top ring land. Valve contact is close enough to the edge that it could be slightly pinched.

definately agree this piston needs to come out and be mic'ed . my S14 theft recovery engine was attemted to be blown up by theives and it wouldnt die so they put pennies in the motor which skippped the timing chain and the result was all intake valves and pistons looking just like the one's in your pics and every piston skirt was bent .002 to .006 (doesnt take much) even with the forged S14 pistons . needless to say it was bored out to a 2.5l using a kit. net result will be piston slap and possible high oil consumption....

[bmwman91]

Hmm...and here I was hoping that I could avoid pulling anything out of the bottom end...damn. So the risk is that the lands will be deformed, which will either prevent the rings from wearing evenly, or that the piston is out-of-round which will cause gaps in the compression ring?

[spdracrm3]

Hmm...and here I was hoping that I could avoid pulling anything out of the bottom end...damn. So the risk is that the lands will be deformed, which will either prevent the rings from wearing evenly, or that the piston is out-of-round which will cause gaps in the compression ring?

yes there is a chance of the top ring land being pinched shut holding ring from moving out against cyl wall or rotating in land. and also with dents like that in piston the force to bend a valve like that had to go somewhere in the piston rod combo and cast rods are strong ,cast/forged aluminum pistons are weak and will be first to bend ,i was surprised how much my S14 piston skirts bent being forged and a fairly beefy piston by todays standards. they keep getting lighter and smaller to meet fuel mileage standards so imagine later model piston such as those in your m42/44 will be more likley to sustain damage....hate to say it but seeing as your that far in better to be safe than sorry down the road ,and pull to measure that piston now rather than do it all again in a few months.