Author Topic: M47 crank + custom pistons, rods, etc. (Read 51141 times)

sheepdog · « **Reply #60 on:** June 05, 2006, 04:11:54 PM »

Quote from: tim_s

i agree. however depending on how many miles you've done you might get away with a re-hone and some new rings. my bores were in surprisingly good condition for a 100k+ mile engine, you could still see the honing marks. the engine i used to make the 2.1 however was too far gone for that.
anyway to me its a bit redundant as imo this wouldnt be the best way to get some bigger capacity on a budget. just throw some massively oversized high CR lightweight pistons in there with the standard crank, put in a lightened flywheel, rebuild the rest of the block and you'd be away. would be much more in character with the m42's revvy nature, you dont want to make it that much of a long stroke imo, and buying a crank, modding it, getting new rods etc is more work than just an overbore. just my $0.02

True.
You bring up a good point though.

Stroking costs money. Boring is relatively cheap.
Bore the block add custom pistions to raise the cr and bore size and call it done. This would be more than likely be cheaper than going to a stroker crank setup and you would get a rebuild out of it.

This also does not increase piston speed (meaning more heat and wear), and will be a simpler setup.

mrjezza · « **Reply #61 on:** June 05, 2006, 08:53:58 PM »

Hmm okay. How much can the block be bored safely?

Also, even though the specific example I gave above wont work, is the maths for shortening the conrods correct... IE you need to shorten the conrod by (stroke/2)mm to maintain stock compression? Also, would a head gasket that is (stroke/2)mm oversize have the same effect?

sheepdog · « **Reply #62 on:** June 05, 2006, 10:58:58 PM »

Quote from: mrjezza

Hmm okay. How much can the block be bored safely?

Also, even though the specific example I gave above wont work, is the maths for shortening the conrods correct... IE you need to shorten the conrod by (stroke/2)mm to maintain stock compression? Also, would a head gasket that is (stroke/2)mm oversize have the same effect?

If I remember correctly 87.5 was the max. Jim from Metric recommends 87. Unless you really want to push it.

tim_s · « **Reply #63 on:** June 06, 2006, 04:02:36 AM »

Quote from: mrjezza

Hmm okay. How much can the block be bored safely?

Also, even though the specific example I gave above wont work, is the maths for shortening the conrods correct... IE you need to shorten the conrod by (stroke/2)mm to maintain stock compression? Also, would a head gasket that is (stroke/2)mm oversize have the same effect?

87mm is the max i'd go to being sensible. if you stroke the engine but keep the same pistons unchanged you will increase the CR, as CR is the ratio of vol at BDC:TDC.

koyota · « **Reply #64 on:** January 24, 2008, 05:09:22 AM »

Quote from: tim_s;6095

87mm is the max i'd go to being sensible. if you stroke the engine but keep the same pistons unchanged you will increase the CR, as CR is the ratio of vol at BDC:TDC.

Hi Tim, would shaving the stock pistons of M42 E36 be very dangerous. I mean the stock pistons are good for boost up to 1.xx BAR. As I posted here http://m42club.com/forums/showthread.php?t=4656 I can get the M47 crank cheap in Bulgaria( 400$ ) and I'd really love the bottom end torque this stroke will give me. The trouble comes with the pistons. I have been told that ordering custom pistons is way too risky, since you can not be sure what will come in the box.

hesgone2fast · « **Reply #65 on:** March 23, 2008, 03:25:53 PM »

Quote from: koyota;41612

Hi Tim, would shaving the stock pistons of M42 E36 be very dangerous. I mean the stock pistons are good for boost up to 1.xx BAR. As I posted here http://m42club.com/forums/showthread.php?t=4656 I can get the M47 crank cheap in Bulgaria( 400$ ) and I'd really love the bottom end torque this stroke will give me. The trouble comes with the pistons. I have been told that ordering custom pistons is way too risky, since you can not be sure what will come in the box.

$400??
Can you get a M47 crank for me and ship it to me for $500 plus shipping(that means you win $100)?

RouteZeroDesign · « **Reply #66 on:** March 24, 2008, 01:45:01 PM »

Can i just add that tim's last post in this thread was june 2006.....i doubt he will be checking back here.

Your probably better off pm-ing him or sending him an email.

Koyota- Ordering custom pistons isnt a problem as long as you get them through a reputable source...and even then, if they show up on your door step and they are wrong, send them back.

ANtiX25 · « **Reply #67 on:** October 16, 2012, 09:24:05 AM »

So I have a question bout this build, im thinking bout doing it also im leaning more towards FI if i get low compression pistons will it defeat the purpose of this build?