How easy is this! Exclude factors like thickness etc cause I'm on that. I mean the top compression area (flat not domed) and perhaps just around the edges mostly, just pondering cause I found a set that ALMOST matches my needs but might land up 0.5mm or so too high for head clearance after factoring in rod stretch/expansion at rpms, zero clearance is not good lol. It's one of the few things I have never tried and I'm not keen on double headgaskets. It's an oversized forged and uncoated piston set made for an sr20det.
This engine is proving to be a SOB to get pistons for at a decent price so I'm considering other options. I kinda half rolled and blew up the churbro honda so want to build it up properly now but the pistons are a pain cause a lot are 11:1 or priced silly.
big.b-lil.c,
Sep 25, 4:07am
yes it can be done i have had it done on two different engines, 440 pistons in a 383 and holden 202 pistons in a ford 2.0l. in both cases they were professionally machined by a engine reconditioner.
muzz67,
Sep 25, 4:16am
used a beltsander once,, worked well!
mrfxit,
Sep 25, 8:47am
Did it at school on their lathes many years ago. 2 Austin A40 pistons turned to match 2 Humber 10 pistons in a flat head Humber engine. Austin pistons had to have shortened skirts, trimmed tops & cut circlip grooves.
Worked really well
Tops & bottoms can be done fairly easy on a FULL SET, but diameter is a totally different matter
mrfxit,
Sep 25, 8:49am
Trimming domed pistons depends totally on the shape of the underneath. area. Some are the same shape as the dome which means you can't take anything off.
pollymay,
Sep 25, 12:38pm
Yeah i know about hollow domes and the issues that come with them. These are JE forged flattop pistons. Seller has provided micrometer specs in the ad which is a first that i've seen but it works out perfect for the bore clearance. Just the compression height is a little off. Would require slight skimming of the rods as well to fit but that's easy, clamp them in the lathe and plane 0.020 off each side of the small end.
I'll think about it.
purple666,
Sep 25, 12:53pm
Custom built head gasket might be your best option.
unclejake,
Sep 25, 1:09pm
Shaving the piston crown down is an easy job in the lathe. The forged pistons I have worked with have had plenty of material to work with.
It is important to weight balance them again afterwards, and to establish a safe crown thickness prior to starting the job.
pollymay,
Sep 25, 2:20pm
I can balance them again after easy peasy. The pistons are sr20, the motor is an H22a. Block has been prepped with darton stuff so is no longer FRM honda bores (which I think are nikasil coated) that eat pistons so I can run what I want. Forged H22 units are pricey, these sr20 ones aren't. They are however 32mm compression height compared to 31mm. A lathe would easily cut them and if it was your usual shitter just being put together I wouldn't think twice but I'm going to boost the balls out of this thing, it should be about 300whp on pump gas being flogged every drive. And getting that power reliably isn't cheap.
I found someone using the h22 rods with sr20 piston tops in a nissan to get more rod length I have however not found someone using sr20 pistons in an H22, the numbers can be made to work however it's always nice to see it's been done then you know.
pollymay,
Sep 26, 2:32am
Crunching the numbers further in depth I get 8.8:1 compression ratio, 2156.73cc, 1.58:1 rod to stroke ratio, 0.04 piston to deck height. As far as I can tell the numbers are pretty good, just I'd really really LOVE if I could find someone who has done this which is doubtful. All well and dandy being Mr First but I prefer when I know things will work out. Due to not having the pistons in hand I don't know if the flycuts are right and hence valve clearances, piston pin to rod bush clearance which should be perfect but you never know and ultimately what the real CC of the piston dish is with the correct fly cuts and machining. I calculate -12cc dish roughly but that is a totally off hand guess'.
Just waiting on seller to confirm shipping is ok to a texas address of extended family to utilize free shipping. It's different to my paypal address and some sellers won't accept that. If they greenlight it then I might pick them up then send rods to the same address and a few other things then do a bulk shipment. Might need injectors and an upgrade fuel pump to, the list goes on and on. Group B spec car if I keep this up.
kazbanz,
Sep 26, 5:46am
Being a negative bastewardwhats occurred to me is if this dont work for whatever reason you are left with a knackered longblock. Given these pistons are being used in a performance situation I'd be reluctant to suggest thinning them even by .5mm I can see your concern regarding timing if you go with a thicker headgasket (NOT two gaskets) but if you get the right kind you have a real win/win.-Get two headgaskets made at the same time and should youn need a new piston in a hurry its off the shelf too.
mrfxit,
Sep 26, 6:48am
Fully agree, Theres several firms around that can laser cut a custom headgasket to whatever thickness you need. You could start with the cheapest material option to get the thickness correct & it won't really matter about blowing a couple of gaskets in testing. Then when it's all set up ready for final testing, get the final gasket cut in the best suitable material done & get on with driving the beast.
mrfxit,
Sep 26, 6:52am
Better to pop a few gaskets then to have a piston break & crack or shred the bore or worse . A chunk of the crown sitting on the top of the rest of the pistonJUST on the final death stroke UPWARDS .>>>>
Yeah that happens. Only other thing is I'm unsure of the flycuts but I can always redo them to. The pistons are about $300 with all the rings, snaplocks, pins etc I need vs honda ones that seem to run for at least $500+ in stock bore size. Stock bore is popular so they sell like hotcakes, an overbore sr20 kit, not so much.
elect70,
Sep 26, 11:33am
I have even cut eybrows in the flat top crownsfor valve clearenceon the worked 340 I hadhead was seriously milledto give 10 .8 Cr& hi lift &duration cam, no problem
kazbanz,
Sep 26, 11:40am
Mate I'll be honest with ya.--I'd just pay the extra$200 for the right pistons. IMO what you are concidering is false economy and could very well end up costing MORE or just as much money as just dropping in the factory pistons. --er that was of course working on $200 a SET difference Had you concidered going one oversize on the factory pistons(maybee cheaper) then boring out to the new size.Brovided the bigends etc are all MINT thats going to give you a fresh engine.
pollymay,
Sep 26, 11:57am
Honda pistons are crap for boost, which is why I've landed up with with that picture you see. You push past 300whp and it's like pulling the pin on a hand grenade. The block I don't want to touch, it was prepared with darton sleeves to stock 87mm bore. The pistons I'm looking out for are forged H22 units and they do come up time to time at a decent price but are popular so are gone fast.
I need some 16 year old to run out of money building their honda to 500hp then sell all the bits cheap lol.
kazbanz,
Sep 26, 12:05pm
sorry pollymay i ASSUMED YOU MEANT FACTORY'SSo I'll edit to read "as just dropping in the Honda aftermarket high performance pistons"
pollymay,
Sep 26, 12:18pm
Yeah these units are the right bore size just I think they will hit. I'm hovering over my paypal account ready to just buy them and check clearances. Semi kinda done this before, I've cut notches into an old valve and done ghetto flycutting before. Had pistons above deck and double gasketed but haven't skimmed a set before.
In their favour is they are dished, it's only the outer edge which is thicker underneath where it meets the skirt that needs machining. Also they are about 2mm down at the edges of the flycuts anyway due to the cuts extending out to the side. Had friends do this before on really custom builds and others that have gone for all out bazillion dollar custom units, it's great having the right items but even they fail and it's even more expensive again they do.
kiwicon,
Sep 27, 8:39am
tried SR20Forum in the states. long shot but worth a crack.
pollymay,
Sep 27, 11:18am
I bought them, actually found the seller on zilvia.net after lots of searching. HATE zilvia but gives me a way to shoot back and forth.
I measured my engine before buying and the engine has more counterbore into the head than I thought. About 0.050 - 0.060, headgasket is 0.026. I'll be about 0.040 above where the old pistons used to be however I didn't think the head had that much counterbore till I actually got onto it. If it works these will actually in theory give a better squish band than H22 units. They can take up to about 1mm above deck looking at other builds of people using H23 stuff to make a 2.3 vtec.
Only thing that remains to be seen is the valve cutouts which overlaying the pictures of difference pistons are close plus it's dished anyway. It's something I just won't know till I try it and measure.
mm12345,
Sep 27, 11:44am
I "adjusted" some pistons on a 2-stroke kawasaki triple bike I used to own many years ago.Cut a "3/4 Maltese cross" on the crowns to adjust transfer and exhaust port timing and direct gas flow (so the theory was), and trimmed a few mm off the bottom of the skirt, to adjust intake port timing.I used simple tools (files etc) but balanced them very carefully using lab scales. It needed some tweaks to fuel (jets) and ignition timing to run well, It was both very successful, and very unsuccessful.The increase in power output was "significant".It would continue to pull very strongly way way past redline revs -you really needed to change gear using the revcounter - as if using "seat of pants" method, I have no doubt it would have revved past the point of self destruction, even in top gear. The unsuccessful part was that this converted what was already a machine with a nasty peaky power band into a suicide machine, with a sudden transition from completely gutless until at about 8,000rpm it would scare the pants off the rider.It developed the habit of unpredictably picking the front wheel up off the ground with the possibility of doing sudden back-flips - when you least expected, between corners in 3rd gear on tight twisty roads etc.So eventually, when the bore got a bit worn, I reverted to standard pistons.The modified pistons I removed seemed to be fine - no sign that they were a risk of flying apart.
pollymay,
Nov 24, 2:49am
I like scary. My plan is to rear mount this engine in a prelude body shell I've built the shit out of with an 8 point cage (might be 10 when I'm done). Turbo is pretty big. The reduced squish area will be beneficial, it's like group B all over again. Wouldn't mind taking it to some road events either, mid engine rwd with double wishbone suspension and decent power it'd tear up.
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