engine and drivetrain Help! Bad Points, Knocks, Won't Start And More!

[Simeon]

Leak down test will show the problem for sure. Not sure I have ever seen figures that low for compression. Valve damage?  Would be tempted to pull the head just to see. It *could* be an easy fix like a head gasket blown between cylinders (as has been pointed out). Slap a new gasket on it, turn a blind eye to other 'while you are there's stuff, button it up and drive it while you build the other engine. 

[Leitrum]

Leak down test will show the problem for sure. Not sure I have ever seen figures that low for compression. Valve damage? Would be tempted to pull the head just to see. It *could* be an easy fix like a head gasket blown between cylinders (as has been pointed out). Slap a new gasket on it, turn a blind eye to other 'while you are there's stuff, button it up and drive it while you build the other engine.

I finally got around to digging into this since the lady of the house is gone for the weekend. I took the suggested route of pulling the head to see what I could see before I go any further. What I found surprised me, but I have to admit I feel a lot better about my abilities. No matter what I would've done, it probably never would have started.

First thing I saw was the head gasket. With a huge hole unit on cyl 1. What Id love to know is where the missing piece of metal went!

Second thing I noticed was this above the hole in the head gasket. What the hell happened?!

Further inspection I caught this on cylinder 2.

So the head is fubar. Looks like I'm back to rebuilding my original engine and seeing what parts I can pull off of this thing to minimize replacement parts I need to buy. Sigh.

Edited August 24, 2014 by Leitrum

[thehackmechanic]

Congrats. You've just saved yourself at least a grand by doing all this yourself. Someone sell this man a head!

 

--Rob

[Leitrum]

Congrats. You've just saved yourself at least a grand by doing all this yourself. Someone sell this man a head!

 

--Rob

 

Hell yeah! On the topic of saving money, I coincidentally stopped into a BMW specialist shop yesterday to chat with them about my situation and see if they did any machine work there or if they had recommendations. He asked me what I wanted to get out of the engine, but as soon as I started telling him what I had in mind, he started berating me and acting very condescending without letting me elaborate (as if there are only fully on race cars and OEM street cars). And then as soon as I mentioned that I usually try to do most of the work myself, the guy pretty much wrote me off and went back to what he was doing before I walked in. If I ever had something I couldn't figure out or not interested in attempting myself (i.e. - head rebuild!), I'm obviously going to bring it to someone. What is it with shops that don't appreciate people who take the initiative to learn to work on their own cars? Anyway, it was disappointing to say the least. 

 

So now I have this situation I have to figure out on my own. Here's what I have at my disposal:

 

Original Engine 

 

- 1976 Matching numbers block (with some scuffing from the skirts?)

- 121 TI head, stamped 69 that I think was replaced sometime before 93 according to all the records I have from PO's (looks solid, but leaking down a couple of the valve stems)

- 88.97 Mahle piano top pistons with some grinding on the corners to get them to fit the 121 head. Also has some scuffing on the skirts that looks to match the block

- Crank that at minimum needs a polish, possibly a grind

- Old style oil pump (3 bolts)

 

 

"New" engine

 

- 1974 Block that seems like it might've had a fresh rebuild - I can still see crosshatching on the cylinder walls but there's a lot of discoloration on the walls too

- Head is dead, but I pulled the cam

- 89.97 (89v1++++) Mahle piano top pistons

- Crank with perfect stock size journals and fluid rotation (actually spins when I turn the block over on the stand)

- Newer style Febi oil pump 

 

And because every post needs a pic in my book, here's one comparing pistons (88.97 on the left, 89.97 on the right). What's interesting to me is the difference in the rings. Do some of the ring sets not have the oil control springs on the lower ring? because the 89.97 didn't. 

 

 

 

Part of me was thinking that the bottom end of the 74 was so tight that I should just thrown my head on and run it, but at this point, I'm kind of feeling like since everything is pretty much apart on both engines, I should do it right and not have to worry about it for a while. I also like the idea of keeping matching numbers from car to body since my original block hasn't been bored at all yet. Should I just see what the machine shop says about the current pistons and bore and go from there? I'm assuming with that direction that I'll steal the better of the two cranks to avoid more work, use the newer oil pump and send the cam I stole off the E12 head out as a core for a regrind to 292.

 

The only question left is on pistons. keeping in mind that I'd love to go to dual 40 Webers at some point in the future, if I don't need a bore and can get by with a hone, would you just replace rings and re-use the current setup or is it worth replacing with 9 or 9.5:1 compression? And if so, where can I even get the higher compression flat top pistons in anything other than 90mm?

 

At the very least, I'll plan on bringing the head to a shop tomorrow morning to get checked out knowing that at minimum I'll be rebuilding that. 

[Guest_anonymous]

have the full piano top pistons speced for usability, If they check out polish the crank and bore the smallest bore block to match pistons, find a proper e12 head to use with those domed pistons. If you use the 121 head find bath tub or flat top pistons, if you use a cam with some lift you will want to clay the valve clearance if you mix and match head/piston combustion shapes even if you grind the pistons or head which can only lead to ancillary issues in the long run. be sure that whatever head you use you have a corresponding upper timing cover to be milled down to the same size.