e30tech.com Forums


Go Back   e30tech.com Forums > Technical > All-Wheel-Drive iX
Register FAQ Members List Sponsors Advertise Shop Search Today's Posts Mark Forums Read







Limited Group Buy: E30 Rear Subframe Camber & Toe Correction Kits - $69 Shipped

Reply
 
Thread Tools Display Modes
Old 06-17-2013, 01:43 AM   #1
EyExR
Senior Member
 
EyExR's Avatar
 
E30: 1991 325iX
Location: Lawn_Guy Land, NY
Join Date: Jul 2010
Posts: 1,186
EyExR will become famous soon enough
Default 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.
EyExR is offline   Reply With Quote
Guest Message
Tire Rack - Pure Control
Old 06-17-2013, 12:16 PM   #2
Tinkerputzer
Senior Member
 
E30: 325i
Location: SoCal
Join Date: Apr 2008
Posts: 357
Tinkerputzer will become famous soon enough
Default

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.
Tinkerputzer is offline   Reply With Quote
Old 06-17-2013, 03:37 PM   #3
chris325ix
Senior Member
 
E30: '91 325ix
Location: bellingham, wa
Join Date: Nov 2005
Posts: 15,574
chris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond repute
Default

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.
chris325ix is offline   Reply With Quote
Old 06-18-2013, 01:46 AM   #4
Tinkerputzer
Senior Member
 
E30: 325i
Location: SoCal
Join Date: Apr 2008
Posts: 357
Tinkerputzer will become famous soon enough
Default

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.
Tinkerputzer is offline   Reply With Quote
Old 06-18-2013, 12:46 PM   #5
jtdogblue
Senior Member
 
E30: 87 325
Location: SoCal
Join Date: May 2010
Posts: 239
jtdogblue is a jewel in the roughjtdogblue is a jewel in the roughjtdogblue is a jewel in the rough
Default

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.
jtdogblue is offline   Reply With Quote
Old 06-18-2013, 03:21 PM   #6
EyExR
Senior Member
 
EyExR's Avatar
 
E30: 1991 325iX
Location: Lawn_Guy Land, NY
Join Date: Jul 2010
Posts: 1,186
EyExR will become famous soon enough
Default

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 is offline   Reply With Quote
Old 06-19-2013, 09:01 AM   #7
EyExR
Senior Member
 
EyExR's Avatar
 
E30: 1991 325iX
Location: Lawn_Guy Land, NY
Join Date: Jul 2010
Posts: 1,186
EyExR will become famous soon enough
Default

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 is offline   Reply With Quote
Old 06-19-2013, 12:09 PM   #8
EyExR
Senior Member
 
EyExR's Avatar
 
E30: 1991 325iX
Location: Lawn_Guy Land, NY
Join Date: Jul 2010
Posts: 1,186
EyExR will become famous soon enough
Default

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??

Last edited by EyExR : 06-19-2013 at 12:12 PM.
EyExR is offline   Reply With Quote
Old 06-19-2013, 01:10 PM   #9
chris325ix
Senior Member
 
E30: '91 325ix
Location: bellingham, wa
Join Date: Nov 2005
Posts: 15,574
chris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond repute
Default

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.
chris325ix is offline   Reply With Quote
Guest Message
Tire Rack - Pure Control
Old 06-19-2013, 02:49 PM   #10
Bullet Ride
Senior Member
 
E30: 325i
Location: The Garage
Join Date: Sep 2009
Posts: 787
Bullet Ride is a jewel in the roughBullet Ride is a jewel in the roughBullet Ride is a jewel in the rough
Default

Quote:
Originally Posted by EyExR View Post
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
__________________
Bullet Ride is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -4. The time now is 11:08 PM.






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