liftin the head help needed

[pointynoggin]

toby you are freaking me out, I hope my machinist didn't screw it up.  He requested the pistons when he did the boring out and as I said I checked the piston to cylinder myself some where in between 0.001 and 0.002in.

I have a std piston in front of me that has less than 10000km in it...


76.28mm at the skirt y=0
76.14mm below oil ring y=41mm
75.90mm above second ring  y=53mm
75.78mm above first ring to landing y=62.5
75.72mm top of piston y=70.5mm

If it is pushed over to the side the protrusion would vary +/- 0.067mm that is a conservative estimate but also doesn't account for lube.

[Toby]

The area of the rings does not even touch the cylinder wall only the area BELOW the oil ring. Only the area that actually touches the cylinder wall is important. If your pistons have .0055" taper from the bottom of the skirt to the area under the rings you are screwed, Measure again and make sure that you are measuring the top of the skirt and not the relieved area around the ring lands.

What is important is what that paper said that came in the box of pistons. It the "machinist" did not read it and follow those directions you motor will be a loud leaker and will likely be VERY unhappy. German pistons are not clearanced like everything else. If Joe Chevy did it like he does everything else, bend over.

[billybobf]

Um, yeah, you should try holding those pistons in your hand for a few minutes before measuring...

you would be amazed at what a piston can do just warming up a tiny bit...

We used to put them in the fridge and measure, then run them under the hottest tap water we could find and measure (just dont get rings or pin wet) we could got one of them to change like .012, thats a crazy difference, and then think of what the piston gets to at operating temps

[smutts]

you would be amazed at what a piston can do just warming up a tiny bit...

The times I am sat in someone elses car, and they blast a stone cold engine to 80mph plus, uphill. I can just feel that engines pain.
Mate has a BMW 5 series, drives as above, can't understand why he has cracked three heads, and counting.
Anyway back to the thread!