PDA

View Full Version : pistons move around in bores

nickmpower
08-26-2007, 10:04 PM
ok well some of you may have heard of all the troubles im having with my engine

well i finally bit the bullet and took it out, after taking the head off i found i could move the pistons around in the bores.

im thinking this isnt right

the first one is the piston moved all the way toward me, the second is away.

http://nicktenhulzen.com/ring1.JPG
http://nicktenhulzen.com/ring2.JPG
bmwman91
08-27-2007, 01:14 AM
As in they can wiggle around noticeably by hand? You should have some words with your mechanic about the pistons he selected for your application.
nickmpower
08-27-2007, 02:19 AM
oh yeah they an wiggle. And I am the mechanic, except the machinist that bored and put the short block together. The Pistons were supposed to be 86.5 and the block bored .003 over but im thinking he might have done .03 on accident.
Naked Assault Gerble
08-27-2007, 02:52 AM
he owes you new custom pistons then.
rob_e30
08-27-2007, 09:40 AM
I guess that explains the blow-by. :(

I would take the whole short block back and have him measure everything. Who assembled the short block? I told the my machine shop what I wanted for compression ratio and over bore and had him specifiy and order the pistons as well as assemble the short block. He lost one or two of the oil sprayers but he told me and I ordered new ones from the dealership.

I'm really sorry to hear you're having problems. Good luck.
bmwman91
08-27-2007, 10:41 AM
oh yeah they an wiggle. And I am the mechanic, except the machinist that bored and put the short block together. The Pistons were supposed to be 86.5 and the block bored .003 over but im thinking he might have done .03 on accident.

Yikes! What is the maximum allowable overbore on these? Is he going to owe you a new block as well?
badboypolar
08-27-2007, 02:06 PM
Max piston to wall clearance is .15mm which isn't much, so .03" is a hell of alot (.762mm). I'd check with the machinest to see what he did. Most machinest will measure the piston(s) then machine the block.
bmwpower
08-27-2007, 02:13 PM
Print this and bring it to the guy.....

Wait...86.5???? You're waaaaay over.
nickmpower
08-27-2007, 02:21 PM
yes these are custom piston so they are bigger then stock
nickmpower
08-28-2007, 06:59 PM
well i just took the block apart with my machinist and everything looked fine. my life sucks
bmwpower
08-28-2007, 09:42 PM
well i just took the block apart with my machinist and everything looked fine. my life sucks

wha? So the movement is normal then? You checked the bores? Did they come out to spec?
asubimmer
08-28-2007, 09:59 PM
you need a new "machinist"
tim_s
08-29-2007, 08:19 AM
Bore looks ovalled or piston not in centre of bore in last pic; may not be much of a prob; does it do that all the way through the bore or just at the top of the bore? what is the bore to piston clearance in mm? shouldn't be your mayo problem though. what did you replace when you built the new engine? is the prob better/worse on new engine? new water pump, lower timing case etc? profile gasket look ok? i've seen a hole above water pump on the block of an m40 before too, that caused water in oil as it got into the timing case. I really hope you get it sorted :(