engine and drivetrain Rebuilding Engine - Misc. Questions

[Leitrum]

As the title says, I'm in the midst of a rebuild following the disaster that ensued here: http://www.bmw2002faq.com/topic/155761-help-bad-points-knocks-wont-start-and-more/

 

For a quick overview without too much detail to make my questions relevant, here's where things are at.

 

 

Things are progressing as fast as I could ever really expect them to- which is to say, never fast enough. Block and head are actually at the machine shop and not still layed out on a table as per above. Both have checked out okay, are ready for machine work and are just waiting on parts now since the IE pistons I want are still out of stock. To fill in some of the goals and background of where this is headed, here's what I have planned. 

 

- Block is still bored at 89mm so I'm having it bored to 90mm to accept the IE 9.5:1 flat top pistons

- Cam is getting reground to 292. As it turns out, the cam that came with the spare engine I picked up in the post I linked above is a 284 regrind so in case I don't like the 292 (not likely), I've got something to fall back on

- Head is a '69 121TI with the small valves so I'll probably have to get new seats to accommodate the larger SS replacement valves. Also getting new stems, single HD springs, rockers, rocker locks, etc. 

- Will probably break the engine in with the 32/36 that came with the engine originally just so I have something easy to baseline, but I also have a pair of matched 40s I picked up from Daron I'm looking forward to using eventually.

 

While the engine is out, I'm also rebuilding the whole front end with new brakes and lines, cleaning the hell out of the engine bay, and probably giving it some rust treatment so the surface stuff doesn't get worse. Finally, I'll probably give the engine bay a coat of paint. For the body paint, I'll go to a professional, but I've got a compressor and sprayer so I'm sure I can manage this much. 

 

As you can see, it needs some love...

 

 

As for my questions, there's only 2 so far. First, is the exhaust, or the header/manifold to be more specific. Mine currently has a fully welded exhaust with no down pipe all connected up to a typical '76 manifold from the emissions days. Not ideal. However, the spare engine I picked up had a Stahl in pretty good shape that I was excited to get to use as a replacement. When I measured the tube size though, it only rang in at 1 3/8". The question is, will I be leaving a lot of power on the table by not having something larger? Or is that just in an ideal situation? I mean, yeah, the 32/36 will suck enough on it's own that maybe it won't matter til I get the 40s on? Is 1 1/2" the ideal for this setup and does it make that much of a difference? 

 

The next question is regarding the two oil pumps I have, one that came with my 76 with a 3 bolt flange, and the one that came with the spare engine with the single center bolt. I pulled them both apart to inspect and both have scoring on the outer rotor and housing. 

 

3 Bolt

 

 

 

 

1 Bolt

 

 

 

 

 

When I measured the lobe gap to the rotor, for the 3 bolt I read .005", for the 1 bolt, .007". Both relief valves looked okay, with the 1 bolt looking perfect. Also, as a bonus the 1 bolt came with the nice feature of the plate between the two halves of the body. 

 

 

So, the question is really, what to do. The 1 bolt generally looks to be in better shape, but still has some scoring and funny enough, measures worse compared to spec of .003" in the Haynes. I'm not incredibly familiar with oil pumps I'll admit, so I have to ask if the .003" is gospel, or if there's a little wiggle room? What tolerances really matter with this thing and can I replace the inner and outer rotor reasonably affordably? What would YOU do? 

 

Many thanks to all who can comment on these questions! 

 

Leit

[M3M3]

The header will work fine for either setup.

Throw both those oil pumps away and get a new one.

[nutbehindthewheel]

yes, buy a new oil pump (and sprocket)

[Parkertii]

i agree with the advice given above. you don't want to go through all of that work just to have an oil pump wear fail and destroy everything that you have done. 

[TobyB]

I agree with Marshall- that is a very good header for fast street work.

 

And buy a new oil pump.

 

Also, get pistons in hand before the block gets bored!

 

t

[Chamonix72]

You might want to rob a bank to pay for that oil pump.

[ray_]

Beef up the LS subframe mount too.

 

Also, get a new oil pump

 

If it were me I'd go for higher compression but I don't dabble in M10s much, so higher CRs may be a bigger can of worms.

 

Cheers,

[peterschop]

You might want to rob a bank to pay for that oil pump.

 

or buy one from a later model with the M10 motor and swap pickups. 

[Chamonix72]

Still not exactly cheap.

[Leitrum]

So, the consensus seems to be get a new pump. The best and worst thing about this forum is everyone always tells you what you need to hear and not what you want to hear. I was afraid this was going to be the case.

or buy one from a later model with the M10 motor and swap pickups.

Since I need a new one though, this is exactly the direction I started looking since the pickup on the later model single bolt pump I have is in perfect shape. Rock auto has the 85 318 pumps for 170 something. I can live with that more than 5-600.

Beef up the LS subframe mount too.

I bought the reinforcing plate for the drivers side engine mount from IE if that's what you mean. That and the control arms are both at the machinist getting welded up.

I agree with Marshall- that is a very good header for fast street work.

And buy a new oil pump.

Also, get pistons in hand before the block gets bored!

t

Glad to hear more than one person say I won't be suffocating the engine with this setup, I don't really want to have to find a whole new setup and sell this one.

And yes, block is waiting for the Pistons, I was just relaying my plan!

Thanks all!

[mac]

When you get tired of waitin' for those pistons that are "out of stock", if you want to, contact me for a set of MAHLEs. 

I'm at: m a c i t z @ g m a i l d o t c o m. 

 

you could have 'em by the end of the week.

 

mac.

Edited September 30, 2014 by mac

[zinz]

I've always liked this article about Stahl headers... see page 2 about "header sizing" and you'll see that in Ray Korman's test, the smaller, 1 3/8" diameter tubes made more torque and hp in mild engines than the 1 1/2" tubes... and not just a little bit more. 

 

http://www.bmw2002faq.com/topic/146220-stahl-header-vs-tii-manifold-response/

 

Ed Z

[Leitrum]

When you get tired of waitin' for those pistons that are "out of stock", if you want to, contact me for a set of MAHLEs. 

I'm at: m a c i t z @ g m a i l d o t c o m. 

 

you could have 'em by the end of the week.

 

mac.

 

I'll give it some thought, though everything I hear about actual Mahle pistons puts them out of my ideal price range given all the scope creep I've encountered - which is my own damn fault for always wanting everything done the right way... Just out of curiosity though, what would higher compression flat top Mahle's cost? 

 

 

I've always liked this article about Stahl headers... see page 2 about "header sizing" and you'll see that in Ray Korman's test, the smaller, 1 3/8" diameter tubes made more torque and hp in mild engines than the 1 1/2" tubes... and not just a little bit more. 

 

http://www.bmw2002faq.com/topic/146220-stahl-header-vs-tii-manifold-response/

 

Ed Z

 

I think I saw that article once, but didn't read it until just now. What a relevant find, I guess I did luck out with that header for a hundred bones! I'll be picking it up from my machinist on Friday who dipped it for me to get it clean so I can take it to get coated, and also flattened the flange that attaches to the engine. We'll see what kind of shape it's really under all the surface rust then. 

 

 

Just to have done the due diligence, I gave the local dealership a call and talked through what I was trying to order regarding the oil pump and the options I had available given the solid intermediate plate and pickup I have at my disposal. He had a few options, the first of which was an actual 2002 pump on his shelf for something like $550! Seems like a rare thing to find anymore, someone should call them and snatch it up. He also quoted me for a new housing, and both inner and outer rotors for around $300 shipped form Germany. I would still need to pick up a sprocket and chain, bringing the total closer to $400 for everything I need. Alternatively, I could still go with the Rockauto.com pump from an '85 318i and swap the pickup for $170+$65 in shipping. The only downside here is It's not a BMW brand, it's an aftermarket OE pump made by BGA over in the UK. Still, I'm leaning towards the latter option because it would also have the new sprocket along with everything in the relief valve being new.

 

At least time is on my side and I can think this through! 

[mac]

A 9.5:1 FLAT-TOP piston isn't going to happen.  Take a look at IE's website piston description and see that it has a bathtub pop-up.

 

after your machinist decks the block and mills the head, with your 121 head and true Flat-tops I'd guess you'd end up with a c/r closer to 9.0:1.  .................................. just my guess.

 

mac.  

[Leitrum]

A 9.5:1 FLAT-TOP piston isn't going to happen. Take a look at IE's website piston description and see that it has a bathtub pop-up.

after your machinist decks the block and mills the head, with your 121 head and true Flat-tops I'd guess you'd end up with a c/r closer to 9.0:1. .................................. just my guess.

mac.

You're quite right. I was thinking of the raised bath tub style, I just didn't type it!

Oddly enough, somewhere in its history an owner put in piano tops and carved them up to fit a 121. Wonder if it will run better just having the right piston type for the head, given the way combustion chambers work...