Diagnosing a Blown Race Motor

#41

I disagree. All he’s trying to do is to establish the state of wear of the cylinders. First one has to figure out how egg shaped the cylinders are, and by extension, much material would have to be removed in order to make the cylinders round and straight again. If the cylinders are eggshaped, that can be established without bothering with the pistons.[/quote]

How can you disagree? To get a relative measurement [to the piston] you have to measure the piston. Point taken about measuring for straightness… Bottom line, he really needs to know both measurements.[/quote]
We’re talking about apples and oranges. I’m talking about straight cylinders and you’re talking about fitting piston to cylinders.

#42

For clarity’s sake, I do need to make sure the cylinders are both straight and sized correctly for the pistons.

#43

My point exactly…

#44

Yes, ultimately both steps, checking the shape of the cylinders, and also fitting the pistons has to be done. But the reason some chaos has entered into this is that I have been oriented on the issue below where lateracer was talking about multiple blocks. I was trying to point him in the right direction for identifying a good block.

Once a good block is identified, then it’s time to fit the pistons to the cylinders.

[quote=“lateracer” post=55136]I sort of have an update on my motor situation that’s more of a question actually.

I’m going to check out a few blocks I’ve found around here. One is supposed to be in really good shape, but the guy wants money for it. A few others are free and supposed to be in decent shape. Old motors pulled for swaps.
[/quote]

#45

Update Time:

Pulled pistons 3 and 4 out (1, 2, 4, 6 were all decent). Spent some quality time on the cylinders with a 240 grit ball hone. Still haven’t found an affordable micrometer that can fit my pistons (hitting sears tomorrow) to do piston measurements.

#3 cylinder is now smooth and straight. There was some pitting near the top when I opened it up, so I may have fixed this cylinder. Ring gaps and piston landing clearance are dead on the money.

I’m not so sure about cylinder 4. There was serious pitting near the top of the cylinder and I’m not sure I’ll be able to remove it all(might be too deep). The ring gap on #4 is within spec, but it’s at the tail end of the wide side of spec, so I don’t think I can take off too much more material.

About the pitting: How do I know when I’ve removed enough material from the cylinder wall? I can still feel the pitting with my fingernail, but just barely.

Pics if it helps:

#46

[size=4][/size][size=4]The pitting is above the top ring area…worry more about the NEW ring end gap and the finish on the cylinder walls…AND the piston clearance.[/size]Chuck

#47

You’re going to hit it with a lighter hone, correct? Maybe 400?

#48

ehhh, it was all a pipe dream; block was confirmed as a goner today.

Finally got my hands on a micrometer. By the time I had removed enough material from the cylinder walls on #4 to make the pitting & scoring low enough to read within spec on the bore gauge, my piston/cylinder clearance was at .0058"

Obviously it would have been nice if everything worked out, but because of this I’ve had enough practice to get my measuring instruments all figured out to where I can get the same reading multiple times - something I didn’t even know I would need to develop a feel for.

#49

On the bright side you got a cease fire that will prevent you from dumping more time into a bad block and lots of good learning occured.

,-Ranger “there’s always a bright side” Gress

#50

All right, update time again for this thread. After my last post I took my new bore gauge (and new bore reading skills) to a local BMW/Porsche dismantler who let me size up a few M20 blocks he had in the warehouse. I found a nice candidate from an automatic that had very little ovalization and took it home with me.

After talking with the owner of Midnight Oil Motors here in San Diego. The owner’s name eludes me at the moment, but he was really nice and gave me a ton of good info and made no money off of me at all. I’m a fan.

Like anything automotive I had to pick two out of three from the fast/affordable/reliable triangle. He pointed me to a machinist they like who does affordable high quality work, but at a snails pace. A few months later, I’m picking up my totally rebuilt stock bottom end with new bearings and rings. I’ll spare everyone the details, but it was a full work up (crank polishing, rod refinishing, block decking, oil passage scrubbing, etc.).

My question is now about break in procedure. I’m not street legal any more, so I can’t take it on a nice highway drive this time. Thoughts on how I should do break in?

I know Jlevie is a fan of the set and forget it style of running at/around 2500 RPM in the driveway for 30 minutes and calling it done. If it’s good enough for him, it should be good enough for me, but I’m a little gun shy about flogging a new motor. Curious as to what others do when the street isn’t an option.

Also, thoughts on using quick seat ring powder (Link)?

#51

my understanding is that the #1 thing break in does is bed the rings to the cylinder walls, which is accomplished via combustion chamber pressure. so get the motor up to temp and do multiple full throttle pulls from 2500 rpm to redline, the more the better. babying the motor is actually detrimental since it doesn’t provide enough pressure to seat the rings.

#52

JTower is right. I went one step further; secured on stands, did multiple part & full throttle pulls in third gear with my left foot on the brake. Of course watch temps carefully.

#53

As in jack stands in the driveway? Hmmm…kinda sounds dangerous, but I could see this working if I paid some attention to securing the stands/car in place.

Making a mental note to turn car around so it points toward the alley and not the house.

#54

Up on four jackstands - no wheels…Done at racetracks by pros thousands of times!

#55

Absolutely positively do not use any break in powder. You have paid a machinist to hone the bores and make them right. The rings will seal just fine.

My break in is as follows… start and verify oil pressure…run motor for 10-15 minutes until it reaches 180 water temp and all the exhaust ports are the same temp (indicates rings seat). Go to dyno and tune. After dyno readjust valves and go racing. Oh yea, use break in oil on dyno, change to racing oil. Chuck