M20B29 w/ Triple Webers into my '71 2002

[The Dark Side of Will]

Also, I thought an 89.6mm crank would fit in the M20 block. Is this not the case? Or does it fit but require way more clearancing?

[Old city bimmer]

man this thread is all eye candy....

[The Dark Side of Will]

The importance is exacerbated by the fact our beloved M20 engines are non-interference.

I know this is "just" a terminology gaffe, but M20's are interference engines.

[TrentW]

Oh god damn.

[tinkwithanr]

Love the progress Andrew. This thing is gonna be so good when it's done.

[digger]

Is there any difference in counterweight radius between those two cranks ?

[SkiFree]

And I pulled the M10! Get to start mocking things up.

[SkiFree]

Will this beast be on display for the open house?

Yessir.

Hey Andrew, met you on Friday last week while picking up swaybars for my bronzit e30s52. Thanks for the small shop tour and it was super cool seeing your project in the flesh! I'll definitely attend the open house.

Looking forward to updates! And I'll stop by periodically to see what's going on since as I mentioned you guys are 10 mins away from work and right off the highway :)

Subbed

Edit: shit. can't attend the open house. I'll be visiting friends in the BMW motherland

Hey, it was great that you stopped by. Thank you for letting me poke around your car.
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ENGINE REASSEMBLY AND STUFF.

First before I forget …... There are two different 84mm cranks that BMW made which will work in the M20.



The first is crank #1748751, as most know it came in the E36 328i, and E34 528i cars.
The second is crank #1432277, this came in E46 323i and E39 528i's.

The second blue-hued (277) crank is a couple pounds heavier but is a very nice crank. I opted for it.

The following clearance work needed to be done to the block in order to fit the crank (the block was from an E34 525i). The specific areas were around the oil return and the bottom of the bores.

Oil Return







Bore Bottom



Oil Pump Auxiliary Shaft (around the casting on the first saddle base). Note this picture was taken after the crank was put in. There was plenty of room between the shaft itself and the crank counterweights.



Hardware lined out.



Measuring thrust.



Back on the engine stand!



Started to slap stuff on the outside. Love torquing that crank nut.



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Crank-nut torquing procedure

(Yes I know for some that this is as simple as making chocolate chip cookies from a Pillsbury roll, for others [like some of my tech calls] it's witchcraft). This is for the later among us. If these instructions are not sufficient you should really put down your tools and take your engine to a shop before you brake something.

Most torque wrenches don't go up to 302ft/lb. So we use the following equation.

(Weight x Distance = Torque), therefore (Distance = Torque/Weight).

This tells me if I input the desired torque setting and my body weight we will get the distance up the breaker bar that I need to apply my body weight. So once I find that spot on the breaker bar, turn until I need to use my complete weight on the bar (my feet off the ground) and the crank no longer turns then bob's-your-uncle.

In my case 302ft/lb. Divided by #160 = 1.8875ft.

Convert .8875 feet into inches: .8875 x 12 = 10.65inches

So I needed to place my weight 1ft.10.65in. up the breaker bar.

Breaker Bar



To stop the crank from spinning I just wedged a hunk of aluminum between a counterweight and the block. For the cranks sake use a material softer than steel. Wood would work if you made sure to clean fastidiously afterwards.



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Piston to valve clearance
(Again, I know to some this is as basic as making a Hungarian Pancake. To others its like learning how to gleek).

Things that can potentially affect clearance: block/head decking, cam lift/duration, piston pop-up, piston valve pocket, valve diameter, valve lash, and valve seat depth.

I know I'm preaching here, but whenever you are building a new performance engine you need to be checking piston to valve clearance. The importance is exacerbated by the fact our beloved M20 is an interference-type engine. I can personally remember several times instances where the clearance was not checked on a new engine (they just “assumed” it to be ok) which resulted in the destruction of a new engine. Strangely, that bit never makes it onto a build thread. Moral; if you ain't sure, get it checked before you turn it on (apparently a good life lesson in general).

Parts needed
-Modeling Clay
-Decent measuring calipers (at a minimum)
-Extra set of NEW head bolts (not used [unless ARP studs])
-Your old headgasket
-All the normal tools needed for a head job

To check the clearance you start by spraying a piston top with WD40 and press some modeling clay on top of the piston's valve cutouts.

Making sure the cylinder head and the block are both at TDC place the head on the block. Then torque-down the head as you would on a new engine (as per the Bentley Manual). Adjust the valve lash on the rockers that line up with the test bore.

Install the water pump/tensioner/cam pulley/timing belt/etc. (as per the Bentley Manual).

Once everything related to the belt and head is mocked up, go ahead and turn the engine over 2-3 times.


Remove the belt and head.

Now rotate the crank so the test piston is sitting at the top of its bore. You should be able to clearly see where the valves left indents in the clay.

Every piston will have a specified amount clearance (if you can't find it, find it.). In my case the new IE/MahleMS pistons required a recommended minimum of .1” depth and .05” radial. The cylinder head had a light skim and I was using the 284/272 IE NewBillet camshaft.

Slice the clay along the midline and measure using the calipers.





This piston/cam combo measured out to have a depth of .15” and a radial of .06”-.07” on the intake valve (exhaust side had oodles of room). So we are good! This also tells me all else being similar there would be adequate clearance if I wanted to run a 288° cam. It also tells me that I would NOT be safe running oversized valves.

And there we go! Now back to finish the reassembly!

[Sh3rpak!ng]

Hey Andrew, met you on Friday last week while picking up swaybars for my bronzit e30s52. Thanks for the small shop tour and it was super cool seeing your project in the flesh! I'll definitely attend the open house.

Looking forward to updates! And I'll stop by periodically to see what's going on since as I mentioned you guys are 10 mins away from work and right off the highway :)

Subbed

Edit: shit. can't attend the open house. I'll be visiting friends in the BMW motherland

[indecline]

Will this beast be on display for the open house?

[SkiFree]

You guys have the right mindset if I was running ARP cap studs. The load spread does distort things 1-2 thousandths. However the bolts are largely the same as factory (they were checked). I use them on M10's fairly often, M20's not too much.

I dropped the replacement block off this afternoon and got some more info. Turns out the distortion is closer to 3-4 thousandths but limited to the front couple caps. That, and some scoring, led the guy to guess a crank let go and the leverage from the belt wobbled the front section.

Fortunately things are still a go for next week!

[ForcedFirebird]

Scheduling ..... line bore pushes the job back another 3-4 weeks. If this other block doesn't pan out then I will go ahead and do it.

Changing to ARPs for mains can aggravate the bores and you may have issues with any blocks. Odd to see bolts, they are usually studs and nuts??

Correct. When changing hardware you really should aline bore as well as resize the rod big ends (at minimum measure for round). The rods don't tend to move very much with BMW, but the mains will.

3-4wk for a bore sounds like a long time for a job that takes less than an hour. :(

[whodwho]

Changing to ARPs for mains can aggravate the bores and you may have issues with any blocks. Odd to see bolts, they are usually studs and nuts??

[oliver.r]

that bay is going to look soooo sick.
im not sure if you have addressed this but what are you going to do with the booster? isnt it going to be in the way?

[knuklehead92]

Scheduling ..... line bore pushes the job back another 3-4 weeks. If this other block doesn't pan out then I will go ahead and do it.

hope it works out man. I love this build. please hurry :) and if your going to let go of the old block pm me please. it would be a nice table lol