S52 pistons in S50 block: What needs to be done?

[BSH]

I have a $$$hifted S50 3.0L motor and I've been thinking about rebuilding it.

What needs to be done to the 3.0L block to fit a set of used S52 pistons?

[BMW M Power]

whew,

i thought i read "i $$shifted my 3.0l" you scared me for a sec!

i'm interested to hear how using the 3.2 pistons will work.

[RRSperry]

Well, 3.0 pistons are 85.790mm

3.2 pistons are 86.365mm

The rods look to be the same #, so, bore out he block to fit the new pistons, provided that there is enough material to do it.

[BSH]

I'm a newbie when it comes to machining a block.

Can you please clarify a few terms for me? What's the difference between boring, honing and re-sleeving?

Do the cylinders need to be re-sleeved and then bored/honed to fit S52 pistons? Or just bored/honed out approximately 0.4mm?

What's a ballpark figure for the cost of boring the cylinders this much?

Are new rings required when re-using these pistons?

[Spencer]

Just a bit of Boring needs to be done like RRSperry said. You'll have plenty of room.

Also, the rods are the same p/n's but I have a hard time figuring out how they used a longer stroke on the 3.2, but used the same sized rods and ended up with the same 10.5:1 compression.

Any ideas? The only thing I can think of is that the 3.2 pistons are "shorter", and have less material on top. If this is true, then using 3.2 pistons w/ 3.0 rods/crank could lower the CR.

[BSH]

Just a bit of Boring needs to be done like RRSperry said. You'll have plenty of room.

Also, the rods are the same p/n's but I have a hard time figuring out how they used a longer stroke on the 3.2, but used the same sized rods and ended up with the same 10.5:1 compression.

Any ideas? The only thing I can think of is that the 3.2 pistons are "shorter", and have less material on top. If this is true, then using 3.2 pistons w/ 3.0 rods/crank could lower the CR.

Here's Bassmaster's explanation...
They will fit your 95 block with a little boring 86mm vs 86.4 mm...But the CR will be around 7.8. The TDC height of the piston will sit about 6-7mm lower in the cylinder,Due to the differences in placement of the wrist pin on the 3.2 piston.I'll have to get my hands on a S52 crank now.

[Spencer]

Thanks Big Lun. So I guess I was right, the pistons are a different shape/construction.

So what are you going to do to avoid a super low CR? Try to find a 3.2 crank?

BTW, you just need a bore/hone job, not resleeving. I would call some engine builders/machine shops in your area and get a quote. They should have a standard price.

Also, if you are re-using pistons, I would probabily use new rings. Can't hurt.

[BSH]

Thanks Big Lun. So I guess I was right, the pistons are a different shape/construction.

So what are you going to do to avoid a super low CR? Try to find a 3.2 crank?

BTW, you just need a bore/hone job, not resleeving. I would call some engine builders/machine shops in your area and get a quote. They should have a standard price.

Also, if you are re-using pistons, I would probabily use new rings. Can't hurt.Spencer,

I just bought a 95 cosmos with a $$$hifted 3.0L. The valves and pistons need to be replaced. If there's no other damage I'd like to rebuild the motor myself. It will be a fun project and a great learning experience.

If it's too much work or simply too much damage, I'll just sell off the cams, crank, etc.

[BSH]

What's a ballpark figure for the cost of boring the cylinders?Anyone?? :dunno

[EMC]

I'm a newbie when it comes to machining a block.

Can you please clarify a few terms for me? What's the difference between boring, honing and re-sleeving?

Do the cylinders need to be re-sleeved and then bored/honed to fit S52 pistons? Or just bored/honed out approximately 0.4mm?

What's a ballpark figure for the cost of boring the cylinders this much?

Are new rings required when re-using these pistons?

About $25 to $50 a cylinder to bore them and have them honed. If possible, they should use a torque plate like VAC does during the honing process.

New rings should only be around $150 for the set....you most definitely need new rings.

If you are sticking with NA, I would keep the 3.0 crank, bore the block to 3.2 liter specs, and buy a set of CP pistons that will give you an 11:1 CR. I know of a local M3 with cams and 11.0 CR....man, that thing sure scoots. Actually, that car was sold to a guy in MN. I think he likes how fast the car is.

[BSH]

About $25 to $50 a cylinder to bore them and have them honed. If possible, they should use a torque plate like VAC does during the honing process.

New rings should only be around $150 for the set....you most definitely need new rings.

If you are sticking with NA, I would keep the 3.0 crank, bore the block to 3.2 liter specs, and buy a set of CP pistons that will give you an 11:1 CR. I know of a local M3 with cams and 11.0 CR....man, that thing sure scoots. Actually, that car was sold to a guy in MN. I think he likes how fast the car is.EMC, thanks for your reply. :)

I'm seriously considering the rebuild of my recently acquired $$$hifted S50 3.0L:
http://img.photobucket.com/albums/v420/trailerparkboy/DSC00783.jpg

As for pistons, I'm thinking about going with Bavarian MaxSil Pistons with rings (http://forums.bimmerforums.com/forum/showthread.php?t=277824). They offer 2nd oversized (.50 over) S50 pistons are $111.60/each + shipping after 10% discount. According to their website, the bore of these pistons is 86.565mm, which is slightly more than 3.2 specs.

[EMC]

Well, if its not an all out race motor...blah blah...then I'd go with those pistons. They are probably plenty good enough. Just make sure you get the pistons, then you get the block work done.

It's only about $20 to have a cylinder bored, but add on $200 to $300 to have the cylinders all honed to match the pistons. You still need to check ring gaps, etc. even if they are supposed to be drop in pistons. Always better to be on the safe side.

If you weren't so far away, I say you should send your motor my way. I'm probably going to offer a rebuild service sometime soon. I've got excellent and reliable sources for everything.

Also...be careful with the cylinder head when its off the car. Don't set it down on anything without making sure that its a clean, softer surface. You don't want little scuffs and scrapes to cause big problems later on.

[BSH]

Well, if its not an all out race motor...blah blah...then I'd go with those pistons. They are probably plenty good enough. Just make sure you get the pistons, then you get the block work done.Basically, this will be a learning project for me...my intention is to keep this motor as stock as possible, with exception to the overbored pistons. The only aftermarket performance mod will be a URI crank pulley, that's it. Stock airbox, HFM, software, etc.


It's only about $20 to have a cylinder bored, but add on $200 to $300 to have the cylinders all honed to match the pistons. You still need to check ring gaps, etc. even if they are supposed to be drop in pistons. Always better to be on the safe side.So $400 is a fairly accurate estimate for refreshing the block? The cylinder head will also need to be refreshed. All 24 valves were bent and I don't know at this time if the cylinder head is cracked. If so...time for a new head!


Also...be careful with the cylinder head when its off the car. Don't set it down on anything without making sure that its a clean, softer surface. You don't want little scuffs and scrapes to cause big problems later on.Hmm...didn't consider that. I haven't handled the head at all. All I know is that the previous owner had the mechanic tear down this motor to observe the damage due to the $$$hift. The owner subsequently mounted it back on the block prior to shipment of the car to me. Hopefully, he took care of it.

[GEN3RIC]

I know of a local M3 with cams and 11.0 CR....man, that thing sure scoots. Actually, that car was sold to a guy in MN. I think he likes how fast the car is.

Yep. He does! :devillook

Sometime I was going to ask you if you still had that JTD Underpanel he was gonna send me. No biggie though.

[BMuu]

I just thought of something, I wonder if I could put in my s50 crank into my s52 and have lower cr for forced induction?? :) the stroke would also be shorter so maybe It would rev faster??

[GEN3RIC]

By FI you're referring to?

I hope you are meaning twin-screw.

Now the way I see it, youre correct but isnt the S50 crank weighted differently? I dont thhink it would work

[EMC]

Yeah, you can put an S50 crank into an S5, but you will need custom pistons. Pin height in the S50 piston is lower than in the S52 piston. It should rev faster, but I don't think it will be enough to make a noticeable difference. My S52 revs fast enough. :)

Eric R ....Ken has that undertray, and has for over a year or more. You don't want it. The back half of it was ground off from when ken had the car towed after getting a flat without a spare. They towed it backwards and the undertray ground off on the road from the wind getting under it.

[GEN3RIC]

Ouch. I dont need it anyways but thanks for the sad story.

Potholes and nails common in MI? :O

[EMC]

Ouch. I dont need it anyways but thanks for the sad story.

Potholes and nails common in MI? :O

The roads here are horrible. You have to be choosy about where you drive. If I take my car somewhere, its usually a slightly different route than if I were take my truck. I've been lucky and haven't had a flat from a nail in a long long time....although I have found nails in tires and have them repaired about every other year.

[GEN3RIC]

The roads here are horrible. You have to be choosy about where you drive. If I take my car somewhere, its usually a slightly different route than if I were take my truck. I've been lucky and haven't had a flat from a nail in a long long time....although I have found nails in tires and have them repaired about every other year.
Yea I figured. Rims were bent & cracked all to hell... :(

[///M3 CRAZY]

sorry to bring back an old topic but can anyone confirm the compression ratio if using s52 pistons in an s50 block? i have a block that is already bored to 86.365 (stock s52 bore). so i can pop these right in.

[EMC]

sorry to bring back an old topic but can anyone confirm the compression ratio if using s52 pistons in an s50 block? i have a block that is already bored to 86.365 (stock s52 bore). so i can pop these right in.

Nope, they won't fit right in. Pin to top of piston distance is a bit different. I think that it would lower your overall compression by a bit. Time for an S52 crank, rods, and pistons!

[///M3 CRAZY]

Nope, they won't fit right in. Pin to top of piston distance is a bit different. I think that it would lower your overall compression by a bit. Time for an S52 crank, rods, and pistons!


that i understand. but what would the end resulting comp ratio be?

[Matt P.]

Benji, I've got a spare 3.0l block lying around in my garage.

PM me if you end up needing one.

[Matt P.]

Spencer,

I just bought a 95 cosmos with a $$$hifted 3.0L. The valves and pistons need to be replaced. If there's no other damage I'd like to rebuild the motor myself. It will be a fun project and a great learning experience.

If it's too much work or simply too much damage, I'll just sell off the cams, crank, etc.

That spare S50 I just mentioned was $hifted.

Taking the motor apart and putting it back together isn't that hard, but the damage is gonna be pretty extremo. In my motor's case every piston made some valve contact and the worst damage was in cylinder 1 where a valve smacked the piston so hard that it broke off and basically rattled around in there till there was a hole in the piston and the top of the combustion chamber looked like Edward James Olmos' face.

Unless youve got a lot of time on your hands I'd suggest selling the parts off (that's the route I chose)...

[BSH]

PM'd you, Matt.

[///M3 CRAZY]

does anyone know what the end resulting compression ratio would be?

[ScotcH]

rattled around in there till there was a hole in the piston and the top of the combustion chamber looked like Edward James Olmos' face.

:lol