rob wild Posted August 10, 2008 Share Posted August 10, 2008 Just sorting out the garage and getting ready for rebuilding my engine. I just wanted your opinions on these CP pistons and weather they are reusable/worth keeping? as i was going to bin them as i will not be reusing them as my block is 87mm. I have measured then in three places and they are the same i.e. 86.45mm. They do have some light marks on the base of the pistons below the rings. These pictures were taken after literally wiping them with a clean rag. I may add that these are pistons to fit a 86.50mm bore. Opinions? please Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted August 10, 2008 Share Posted August 10, 2008 (edited) Well looking at the crowns, it looks like they have been in a running engine? but not for long looking at the skirts, almost like they have been turned over in a badly lubed or dry bore, but they don't look bad, forged i presume? Edited August 11, 2008 by Tricky-Ricky (see edit history) Quote Link to comment Share on other sites More sharing options...
rob wild Posted August 10, 2008 Author Share Posted August 10, 2008 Well looking at the crowns, it looks like they have been in a running engine? but not for long looking at the skirts, almost like they have been turned over in a badly lubed or dry bore, bur they don't look bad, forged i presume? Yeah thats what i was thinking the engine has been running but it looks like some how it was running dry for a short period of time may be when it was first being started The pistons are forged. Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted August 11, 2008 Share Posted August 11, 2008 They look fine to me, but you need to measure them all axis with a proper micrometer to check they haven't worn or become misshapen. Quote Link to comment Share on other sites More sharing options...
rob wild Posted August 11, 2008 Author Share Posted August 11, 2008 They look fine to me, but you need to measure them all axis with a proper micrometer to check they haven't worn or become misshapen. Thanks Chris Yeah i'll get them measured up a bannister's my local machine shop later On a side note Chris, Phil (terminator) said you had a quick look at my new pistons the 87mm KS ones Have you used KS ones before Chris? I was going to get them anyway but what your opinion on them? Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted August 11, 2008 Share Posted August 11, 2008 Karl Schmidt pistons are very well respected, i wasn't aware they listed a forged piston for the 2JZ engine though. I have used them in some Volvo race engines, and they are used in plenty of high end applications, I'd have zero worries about the quality of them! I suppose the ultimate pistons outside bespoke F1 stuff are Omega, but they invariably have lengthy delays getting stuff ready and they are not cheap. They do know how to make light and very strong piston though, and make all their own rings, so none of this filing nonsense you get with generic ring packs from the US piston makers. Quote Link to comment Share on other sites More sharing options...
dandan Posted August 11, 2008 Share Posted August 11, 2008 I run Omega pistons and their rings in two of my other cars - both NA though. Excellent pistons, highly recommended. Do they do a 2JZ piston? Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted August 11, 2008 Share Posted August 11, 2008 Doubt it, unless something else is close, or someone has ordered a batch to be made. Quote Link to comment Share on other sites More sharing options...
TLicense Posted August 11, 2008 Share Posted August 11, 2008 They look fine to me, but you need to measure them all axis with a proper micrometer to check they haven't worn or become misshapen. It's quite a coincidence that this thread has started today as yesterday I measured my brand new CP pistons on a CMM machine at work. I spent quite a bit of time scratching my head to be honest as I measured as I was trying to measure the diameter at the gauge point. (It's given on the spec sheet, but I would never trust something supplied by the manufacturer.) What I found is that the pistons are not round at all. The only place they actually matched the spec sheet in terms of a given distance from one side of the piston to the other was on the "high" points perpendicular to the wrist pin axis. As I measured around the skirt you could see the piston is actually an elipse of some kind. However, that said what it also showed was that compared to each other the pistons were bloody precise. There are no tolerances supplied from the manufacturer, so I can't say if they were particularly accurate or not though. I'll post up the actual measurements later this evening.... Quote Link to comment Share on other sites More sharing options...
spartan Posted August 11, 2008 Share Posted August 11, 2008 It's my understanding that they're not meant to be round but elliptical in shape when cold, to take account of the fact that the extra material around the small end pin absorbs more heat and consequently expands more. Therefore, when hot, the piston should be round. Quote Link to comment Share on other sites More sharing options...
rob wild Posted August 11, 2008 Author Share Posted August 11, 2008 Instresting I suppose they are engineered like that to allow for the expansion. Are yours for a 86.5mm bore Tony? Would be helpfull if you could give details of your measurements and where you measured them so i can compare them to mine. Cheers Rob Quote Link to comment Share on other sites More sharing options...
TLicense Posted August 11, 2008 Share Posted August 11, 2008 It's my understanding that they're not meant to be round but elliptical in shape when cold, to take account of the fact that the extra material around the small end pin absorbs more heat and consequently expands more. Therefore, when hot, the piston should be round. That's what I put it down to. Makes it a hell of a machining though! Quote Link to comment Share on other sites More sharing options...
dandan Posted August 11, 2008 Share Posted August 11, 2008 It's my understanding that they're not meant to be round but elliptical in shape when cold, to take account of the fact that the extra material around the small end pin absorbs more heat and consequently expands more. Therefore, when hot, the piston should be round. You are correct - differential expansion (same rate, just different amounts of material) mean that the piston skirt is not circular when cold. Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted August 11, 2008 Share Posted August 11, 2008 They are often barell shaped too, for the same reason, or for friction reduction. Honda made a production bike engine with pistons very far from round I recall, but the idea of that was to allow an 8 valve per cylinder head design, as far as I know. It was a follow on from one of the NR race engines, but the idea never caught on. Quote Link to comment Share on other sites More sharing options...
dandan Posted August 11, 2008 Share Posted August 11, 2008 I think that engine was "pushed out" under some sort of homologation ruling but from what I recall it was a bit of a blinder. I can't remember the details...maybe it was a flop or just too expensive to machine at the time? Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted August 11, 2008 Share Posted August 11, 2008 http://en.wikipedia.org/wiki/Honda_NR Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted August 11, 2008 Share Posted August 11, 2008 Here you go, Quote Link to comment Share on other sites More sharing options...
TLicense Posted August 11, 2008 Share Posted August 11, 2008 (edited) My measurements were as follows:- 1. 86.422 2. 86.422 3. 86.419 4. 86.427 5. 86.415 6. 86.418 According to the datasheet that came with the pistons they should be 86.4235 so the biggest deviation is 0.0085mm. These were all measured at the gauge point which is 12.7mm from the bottom of the skirt. Also to note is that the bore diameter for these pistons should be 86.512mm +/- 0.005mm for an average road/race application. This gives a nominal cylinder - piston clearance of 0.089mm. Hope that helps! Edited August 11, 2008 by TLicense (see edit history) Quote Link to comment Share on other sites More sharing options...
rob wild Posted August 11, 2008 Author Share Posted August 11, 2008 My measurements were as follows:- 1. 86.422 2. 86.422 3. 86.419 4. 86.427 5. 86.415 6. 86.418 According to the datasheet that came with the pistons they should be 86.4235 so the biggest deviation is 0.0085mm. These were all measured at the gauge point which is 12.7mm from the bottom of the skirt. Hope that helps! Thanks Tony that does help i'll check mine tomorrow Quote Link to comment Share on other sites More sharing options...
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