e30tech.com Forums

e30tech.com Forums (http://www.e30tech.com/forum/index.php)
-   All-Wheel-Drive iX (http://www.e30tech.com/forum/forumdisplay.php?f=39)
-   -   Bottom End Rebuild (http://www.e30tech.com/forum/showthread.php?t=117652)

EyExR 06-17-2013 01:43 AM

Bottom End Rebuild
 
Is it possible to do a stroker on the bottom end and leave the top end stock?

I just had the head rebuilt stock but now need to rebuild by bottom-end (again... if you've been following my saga.. ).

Anyway, here I am. Engine is out and I need to rebuild the bottom end because I'm losing compression across all cylinders due to a botched rebuild by a crack machine shop in Queens. I'm thinking they tried to put poor rings on all cylinders with worn/mismatched ring lands... that's my theory anyway...

I'm just wondering what I can do to the bottom end while keeping the head stock.

Tinkerputzer 06-17-2013 12:16 PM

Well it is possible but you won't be taking advantage of the engines full potential. At bare minimum install a cam. But it's hard to stop there.

What bottom end were you planning to use? If it's just an eta bottom end i wouldn't waste the effort and stick with stock.

chris325ix 06-17-2013 03:37 PM

sure - I'm thinking the M52 bottom end dropped in your block with I think stock M20b25 pistons should work well, even with a stock cam. lots of torque.

Tinkerputzer 06-18-2013 01:46 AM

Keep in mind you need eta 130mm rods and some extra block decking to make the m52 crank work. Chris is right though. It will be a low end torque monster with a stock cam.

jtdogblue 06-18-2013 12:46 PM

M52 crank+rods+pistons into m20:

Your only clearance issue will be at the counterweights on cylinder 3 and 4 barely kissing the block near the crankcase vent gallery. A little grinding should fix that.
M52 pistons protrude over the deck 2.6mm with this setup. Plenty of room to shave the pistons down to whatever c/r you want then cut valve pockets. (This is my plan, as m52 has lightweight rods and pistons, plus a better rod:stroke ratio)
I forgot who did this recently but it worked out pretty well, he shaved 3mm total. I'm sure if you used a 81mm crank it is still possible with much less piston shaving involved.

Next option is M52 crank, eta 130mm rods, "i" pistons, and a shaved head.

With this setup I believe the CR is around 8.7:1. All counterweights must be bobbed -5mm (not sure if that's diameter or radius, I think it's radius) or else the short rod + i piston combo will cause the counterweights to strike the pistons.

Either way you go there will be custom machining involved, keep that in mind.

EyExR 06-18-2013 03:21 PM

Thanks for the feedback, guys. I just dropped off the block and pistons to be checked out. From the first look at the rings, I was exactly right. The original shop in Queens put the wrong damn rings in!

We'll see what the new shop says, then I'll take it from there.

Is this sort of work typical for a machine shop? Swapping out cranks, pistons and rods, with custom machining involved? Could get expensive very quick, no? Or am I making a bid deal out of nothing?

Where could I source these parts on the cheap and guarantee that they'll hold up?

EyExR 06-19-2013 09:01 AM

Let's say I get M52 crank, rod and pistons... Would the average machine shop know how to grind and machine things? Including all shaving, bobbing, etc.?

What should I expect to pay for work like this?

Thanks in advance!


...oh! and does the crank, rods or pistons have to be brand new??

EyExR 06-19-2013 12:09 PM

Okay. Let me see if I have this right:

I can pick up a used M52 crank and used 130mm eta rods and keep my original pistons. Put on new (correct) rings, have the counter weights bobbed -5mm, and have the head shaved (by how much?).

Is it really that straight forward? Are there ANY other changes that need to be made?

What about bearings and seals?? Head Gasket? Head bolts??

chris325ix 06-19-2013 01:10 PM

personally, I think using M52 pistons is the better method - better CR (anything you want), better rod ratio, better/lighter/stronger rods, etc.

a little more machining but still much less costly than new forged pistons.

I'm not a fan of mods that require shaving huge amounts off the head or block to get a decent CR. that also messes up the cam timing - so now you have to add the cost/headache of an adjustable cam gear.

Bullet Ride 06-19-2013 02:49 PM

Quote:

Originally Posted by EyExR (Post 1363968)
Okay. Let me see if I have this right:

I can pick up a used M52 crank and used 130mm eta rods and keep my original pistons. Put on new (correct) rings, have the counter weights bobbed -5mm, and have the head shaved (by how much?).

Is it really that straight forward? Are there ANY other changes that need to be made?

You will also need to have a spacer machined for the front oil seal, and it's the block that will need to be machined 0.5mm, the head can be left alone.

I've built this motor combination, here's my build thread http://www.e30tech.com/forum/showthread.php?t=112985


All times are GMT -4. The time now is 12:53 AM.

Powered by vBulletin® Version 3.6.8
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.