Machine Shop Woes

[Glliw]

Hey guys, been awhile since I've been on here, mostly because I haven't touched the car recently. Well, past week or so I started the teardown of a spare 6 bolt longblock I got for cheap from a friend in unsure condition. He said the balance shafts spun a bearing. I tore the motor down to find nothing really out of the ordinary. I took everything(pistons/rods, crank, block, and full head) to the machine shop to have it all checked out since I was wanting to re-use as much as possible.

What the machine shop told me after about a week is that the block, crank, and rods are fine. The head needs to be resurfaced, the pistons "shrunk", and that all 8 intake valves are bent.

They said I'd be able to go standard size on everything so that's a good thing for now.

The thing is, I checked the timing before I pulled the head off, and it was dead on, and no valves seemed to be bent when I stared at the head in my garage. Also, what the hell is a "shrunk" piston? The machinist explained it to me, then I asked a few guys that have been building motors for 30-40 years and said they've never heard of it before...is the machinist being a scammist about this?

 

[GVR4592]

Find a different machinist, the one you're dealing with is an idiot, a liar, or both.

 

[bling5tatus]

yeah tell him you're gonna shrink his head before he gets a chance to shrink any pistons you own.

 

[Glliw]

That's what I thought, unless he has some really good reasoning next time I talk to him, I'm gonna take my place elsewhere. The guy seems really unprofessional over the phone the way he talks. Its not just 4 cylinder hate, he's a dick to my friend with a 460 as well.

 

[silver bullit]

Pistons dont shrink unless you melt them, find a new someone to work on you stuff.

 

[laserspeeddemon]

Get you're stuff back on do your own test. Put the "bent" valves back in. And pull up on them (you don't have to put the springs back it doesn't hurt and you can test all the valves at once), and spray the ports with WD-40. There should be no/little fluid moving past the valves. A drip is fine a stream is bad.

And I never heard of a "shrunk" metal. I've heard of metal expanding after heating, but not shrinking. Then again, alot of a my other car buddies don't use the same jargin or slang as I do when we talk about cars. So that could be the case here.

 

[Glliw]

Yea, I went and got my stuff from them today. Cost me $125 for clean block, check line bore, check head for warpage, and disassemble the head. I didn't even tell them to disassemble the head.

When I got it all home, I rolled a couple of the valves around on a table. None of them were bent at all. They all looked fine to me too. A friend's dad said if I were to put them in a bench drill and spin them I could tell better.

They also said that my line bore is really tight and "might work" so I guess I'll be having to go .020 over

Man, I really hate getting dicked with by people.

 

[laserspeeddemon]

I wouldn't pay for that. I would get my stuff and go. If they have a problem. I would just tell them I'll have an attorney call them and then call the police to file a report for fraud and possession of stolen property. They can't do work that you didn't authorize them to do and then charge for it. Then try to keep your stuff hostage until the paid for it.

Also I would make sure they know I would be seeking compensation for the additional downtime my car suffered while the court process takes place.

**edit** This is also why I get my estimates in writing.

 

[Glliw]

I actually don't mind much about the head part though, considering after looking more closely at the bill, they only charged 20 bucks and did a pretty good job cleaning it.

Now, off to never never land of finding a new machinist and choosing rods/pistons.

 

[biglady112]

Don't mistake a collapsed piston for a "shrunk" piston. I have had four different local machinist tell me the same thing about numerous sets of pistons for various motors. If is common on a lot of engines, both forced inducted and naturally aspirated to have the piston collapse a little. This just simply means the skirt is not the same size as stock or is smaller than the others in the set.

Steven

 

[Glliw]

In both times I talked to him about it, for a good 10 minutes each time, he never said collapsed. He said a piston shrinks when it is heat cycled too much and forgets how small it is supposed to go and goes too small when it shrinks back.

 

[bling5tatus]

Guys pardon me for pointing out the (what I believe to be) obvious... but collapse and shrink sound like VERY similar things to me. Some people say grey, some people say gray.

 

[Big Woo]

Perhaps you should take your parts eslewhere, maybe somewhere with expierence specific to DSM's.

It is possible to bend the vales yourself during assembly/disassembly if one is not careful. Either by rotating the crankshaft or camshafts after the timing belt has been removed.

"Shrunk" pistons, well that is sort of an old school term for pistons that the skirts have collapsed. This is a relative term though we are talking about .005 or os here. This is not something that happens from sitting around un-used, it can be caused by excessive heat build-up in the piston.

Piston to cylinder clearance is a Pass/Fail test, either the measured distance is within specification or not. To determine where the fault is you must measure the pistons diameter and campare them to published standards, again either they are in or out of spec. Them do the same for the cylinders, if the piston to wall clearance is not correct then either one or both of these dimension verifications will fail.