Smoke on start up?

[SpecRaceM5]

So my 325i was smoking a little on start up and then went away. It was basicaly once it turned over, a puff of smoke would come out and then it would be done. Then at the track day after a 20-30 min run group, I parked the car. When I started it back up 45 min later or so, it was smoking bad so I shut it down and didn't drive it the rest of the day until it was time to go home. Made it all the way from Willow Springs to Temecula with no problem. Smoked onstart up, but once I was driving for a bit it went away. I thought it was the valve guides so I was told to run a compression check on the motor. Dry first and then wet and if the compression went up a fair amount then it would be the rings on the pistons, and if not then it would be the valve guides most likely. I ran the test and the compression was all in spec wich leads me to believe it is not the valve guides. However, now that I think about it, the Bentley said to test the engine at normal opperating temperature and at that temp, it may have expanded things enough to give me good compression even though the valve seals/guides are bad. Regardless, what is everyone's take on this? Any other tests I can run to find out what the problem is?

Cheers,

Brian

[trent]

Valve guides won't leak compression, if the valve is sitting on the seat correctly. Your compression could be fine with very worn valve guides/seals.

[euroshark]

Its pretty cheap to have them replaced too. The machine shop that does most of the work for Bimmerhaus (look em up, they rule) did my M30 head for $183. Valve job, milled it a bit, installed new guides and seals. I have never experienced a smoother M30! When I have my 3.2 done I'm going to have the pistons and rods balanced too... That should be nice!

[SpecRaceM5]

How difficult is disassembly and assembly? I was thinking of building a motor form the ground up. Obviously I would need to take it to a machine shop to have the machine work done, but would it be a problem to take them a bare block or head and say you want x done to it or is it easier for them to just disassemble it themselves?

Trent: Would blown valve guides cause the burning oil I am experiencing? The theory was that the oil was seeping past them and on start up it would burn off and be done. If this is correct, then how does oil seep past the valve guides, yet blown valve guides do not lower your compression? I am not questioning you, I am just curious for my own knowledge.

Regards,

Brian

[trent]

Trent: Would blown valve guides cause the burning oil I am experiencing? The theory was that the oil was seeping past them and on start up it would burn off and be done. If this is correct, then how does oil seep past the valve guides, yet blown valve guides do not lower your compression? I am not questioning you, I am just curious for my own knowledge.

Yes answer to first question. On an engine with a small cam without much overlap (M20), the valve is closed on compression - so compression doesn't blow by it to go past the valve guide. The opposite is true, with the vacuum of the piston moving down, and the valve open pulling air, it pulls in oil through the guide/seal.

[euroshark]

Building the motor is easy. Assembly isnt very complicated, and doesn't require many special tools for the top or bottom end. The cam can be installed by you if you are a little creative, but usually the machine shop will put the valves, retainers, springs, etc back in for you since that requires a tool that they ALL have.