springersrolla Posted February 17, 2009 Report Share Posted February 17, 2009 from what ive read on the tough k series motor fAQ the 3k pistons are better than the repco 4k pistons. Am i right in my thinking that if i got a reasonable block, with pistons that aren't undersized or worn, i can use these in a 4k block??? Quote Link to comment Share on other sites More sharing options...
dfunkt Posted February 17, 2009 Report Share Posted February 17, 2009 from what ive read on the tough k series motor fAQ the 3k pistons are better than the repco 4k pistons. Am i right in my thinking that if i got a reasonable block, with pistons that aren't undersized or worn, i can use these in a 4k block??? http://www.rollaclub.com/faq/index.php?title=Main_Page ^^^ all the info you need to answer your question is in there ^^^ Quote Link to comment Share on other sites More sharing options...
springersrolla Posted February 17, 2009 Author Report Share Posted February 17, 2009 looked there many a time, just trying to clarify whether its common, or someone has done it before, i assumed there the same size, different rods, and the pistons in the 3k are better than the 4k ones cheers Quote Link to comment Share on other sites More sharing options...
philbey Posted February 21, 2009 Report Share Posted February 21, 2009 Doesn't look like it'd be a problem, although I'd be concerned about a 35 year old piston demonstrating fatigue issues (aluminium alloy). My 5K pistons cost 160 through my engine builder for 40 thou oversize. They are actually a Mahle item. Given that Mahle make OEM equipment for Porsche I can't see where you'd go wrong. Quote Link to comment Share on other sites More sharing options...
rob83ke70 Posted February 22, 2009 Report Share Posted February 22, 2009 3k pistons do NOT fit in a 4k block the cut out on the bottom of the piston is shallower and they hit the counter weights on the crankshaft. buy a new set of acl pistons, you won't regret it. I re ringed a 4k when I was back in high school on a strict budget, and found a piston cracked, tried to fit a 3k piston and found this out. I ended up getting a 2nd hand 4k piston and fitting it. Now this is where I would like to bring up another point that is very important: If you are using 2nd hand pistons, or re using pistons, measure how much the ring grooves are worn!!! I didn't do this and they were worn excessively especially the 2nd hand piston that I put in, and all of my compression rings snapped 10,000 km later, with pieces of ring working up the side of the piston and mashing up the combustion chamber and piston badly. They were all broken and had been for some time, you could tell because the car was down on power and not sounding as crisp as it ought to. If you are rebuilding an engine, I would strongly reccommend that you buy new pistons. If the lip on the top of the bore is not too big, and the bore is not overly worn, and your budget is very tight, I would buy new acl standard pistons and fit them. The acl pistons are miles better than the standard repco pistons that came in the car. The repco ones were prone to cracking as well. Robert. Quote Link to comment Share on other sites More sharing options...
philbey Posted February 22, 2009 Report Share Posted February 22, 2009 (edited) That's a good point about the piston skirt on the 3k, I will add that to the FAQ - Should be mentioned in the "Build a tough K series" article but that's locked for editing. EDIT - Added it to the Blocks article with the info on bore sizes. Edited February 22, 2009 by philbey Quote Link to comment Share on other sites More sharing options...
kickn5k Posted February 22, 2009 Report Share Posted February 22, 2009 My 5K pistons cost 160 through my engine builder for 40 thou oversize. They are actually a Mahle item. Given that Mahle make OEM equipment for Porsche I can't see where you'd go wrong. ACL = Mahle Well Mahle own ACL now and alot of ACL ring sets now come in MAHLE boxes but are not made in germany. stu. Quote Link to comment Share on other sites More sharing options...
Taz_Rx Posted February 22, 2009 Report Share Posted February 22, 2009 ACL = Mahle Well Mahle own ACL now and alot of ACL ring sets now come in MAHLE boxes but are not made in germany. stu. Yeah we've got a couple of ACL plants here in Launy. :) Quote Link to comment Share on other sites More sharing options...
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