How much oversizecan i bore before i need new pistons!
budgel,
Jan 22, 2:00pm
None . Any overbore will need new pistons.
rob_man,
Jan 22, 2:07pm
You can knock the lip off and hone the bore if it's not too worn. Then you can fit new rings if the pistons aren't too worn. From memory it's about .006" of bore wear.
hijacka,
Jan 22, 2:50pm
Depends on the engine really, ej20 can be bored 0.5mm before needing over sized pistons says subaru, I rebuilt mine bout a month ago and took 1 of the bores out to 0.7mm because ofafew deep scratches and it runs sweet. haven't comp tested it yet as its still running in but runs mint and no smoke. Heres a idea.Pop the comp ring inside the honed bore and measure the gap in the ring with f/gauge and compare it to a bore that hasn't been honed. now whats the difference!
bentcoupe,
Jan 22, 2:56pm
Hi all,Its a bike engine,Guy has been quoted $900 for hone and piston!Havnt seen or tried to measure it up yet,Was considering taking a 2 thou cut out of the barrell in lathe before running the glaze buster thru it,
mechnificent,
Jan 22, 3:29pm
$900 sounds like it must be a nikisol bore that needs re chroming. Most bikes are about $100 to bore and pistons are about $200-300. You can't bore anything out without a new piston.
Over-sized bores come in .25, .5 .75 and 1.0 mm, which equates to .010, .020, .030, .040 of an inch.
hijacka,
Jan 22, 3:31pm
No,I don't think that would warrent oversized pistons. Sounds like it just needs deglazing!
mechnificent,
Jan 22, 3:31pm
Tell us what make. if it's a harley you need to clamp the barrels before boring and they rip you off for that.
If it's a nikosol it probably doesn't need boring at all, just cleaning with acid to remove the old piston stuck inside there.
mechnificent,
Jan 22, 3:35pm
And Hijack. you didn't bore your subaru at all, if you had then the piston would be slapping around in there and it would be smoking so bad it wouldn't run. If you do bore then out to .25 of a mill, you need new pistons, let alone .5 or .7.
hijacka,
Jan 22, 3:37pm
bullshit! i did dickhead and have plenty of prove.don't make me prove you wrong again like i did on the subaru rs gearbox subject.remember that one!
bentcoupe,
Jan 22, 3:39pm
vn 800 kawasaki
bentcoupe,
Jan 22, 3:42pm
You need a hug bro, Hey i used to fit engine kits for International harvester,could get factory oversize rings for std pistons We would hone/glaze bust out the clys and bang them together
hijacka,
Jan 22, 3:44pm
Haha.yeah im keen
mechnificent,
Jan 22, 3:45pm
You bored one bore out to .7 of a mill and then what! Stuck the old piston back in! Or did you rumage around out the back and find something that fitted in there did you! And did it vibrate afterwards! I'd have thought the clattering and smoking would have been enough to put most people off even starting it but oh well, it takes all sorts.
So who are these people that pay ou $100 dollars an hour to work on their cars! They would have to be some of your dipshit boyracer peers wouldn't they, to be stupid enough to listen to your crap. Surely there can't really be many of them around, certainly not enough with any money left anyway. So where do you find them!
hijacka,
Jan 22, 3:52pm
Actually i changed the heads and used gtb pistons that matched the head and used my closed deck block with new ringset and full gasket set and valve grind. I couldn't give a rats if you believe me or not but fact of the matter is that subaru says no more than 0.5mm and i went over that and the car runs mint. If you don't believe me ask zarnah on clubsub because he has seen it in the flesh and i got the ringset off him.you don't know me so stop acting like you do andplease stop with the bull crap mechnificent your going to end up looking like a fool with your pants on the ground!
mechnificent,
Jan 22, 4:00pm
Well The Vn should be able to tolerate a bit of wear in the bores. What you need to do is check for wear in the bores, and wear on the pistons. the easiest way for you if you don't have measuring tools is probably to get some feeler gauges and measure between a piston skirt and the bore. Measure at the top and the bottom of each bore, and measure forwards and aft and also sideways. Once you gave all the measurements it will just be a bit of maths to figure how much taper there` is in the bore, which will be the main wear, and how much clearance the pistons have.
mechnificent,
Jan 22, 4:01pm
Yeah rightho Jackoff. You the man!
I hope the one piston will be alright in that loose bore though. It seems a shame to have done that.
intrade,
Jan 22, 4:14pm
there is special oversize rings you can fit but i think it is minimal when you have to boor a blockyou usually need new pistons As just honeing and slapping in new rings is a poor joob and usually wont last long as you cant magically make a egg shaped boor round again and new rings are not egg-shaped to mach the boors. I know if i rebuild a engine it always gets it all newthats pistons rings all gasket and bearings and you need to check conrod top gudgeon pins also. a halfarsed job never pays out.
mrfxit,
Jan 22, 4:32pm
LMFAO . Back in the day . (frick that makes me sound old) Use to do a LOT of rebuilds on english & GM/Holden engines with a few jappa's thrown in. Hardly ever used new parts. NEVER had a failier or smoky engine All lasted at least another 40-50,000 km's before getting smoky again & THEN maybe, needing a full recondition, mostly a part recon.
"It's WHAT you know & HOW you do it that makes the difference" Seen plenty of recon motors fail within a few thousand km's,. Seen plenty of home rebuilds using new parts fail early Also seen some real genius rebuilds & recon methods that have been prooved correct but rubbished by "the pro's".
Been there done that (yes body's getting on but the brains wide awake to new ideas & consistantly proved odd/old ideas)
mechnificent,
Jan 22, 4:38pm
You are right in everything you say here Mr, it is how you do the job that makes the difference. I can rebild motors, using my experiance and discresion, and they do another 160,000km gauranteed. no rebore unless it's needed, no new pistons, no crank grind.
There is far too much "do it once and do it right" bullshit out there covering incompetence and too much bullshit excusing bad workmanship being done even with the do it once and do it right approach.
mrfxit,
Jan 22, 4:59pm
Most of todays drivers that get a recon /rebuilt engine DON'T understand about how to "run in" a rebuilt or recon engine & simply drive it "as per normal".
1 perticuler infamous engine I rebuilt was4.2 sx6 jag motor. Come in FRIED, guy had driven it from the lower Auckland motorway from just above Bombay to Hamilton with NO water. It had .
Cooked the oil dry Blackened the bores Ground off the bearing white metal & most of the bearing backing shells. Crank journals were black 3 pistons had holes in the domes 3 pistons fell apart when lifted out of the bores
Rebuilt with .
Rebore to suit s/h oversize pistons New rings New gaskets Crank "crack tested" & reground New bearing shells Head"crack tested" & planed with new valve guides fitted. Cams & valves checked & refitted
Went fine after that. Point is that even tho the engine was badly cooked, because we did our homework on testing & checking parts, the whole engine assembly was still able to be used reliably. He often returned for oil changes & wof work over the next few years with no work needed doing on that engine
rob_man,
Jan 22, 5:01pm
You're right in a way, I've rebuilt plenty of my own engines and never had a failure. I've pushed the envelope a few times and done things the pros would have shied away from but the risk was my own. It's a different kettle of fish when someone's paying to have work done though, they generally need to be assured that what they have repaired or rebuilt is going to last the distance and don't want to shoulder the risk themselves. In that situation the repairer doesn't have too many options.
poohy99,
Jan 22, 5:11pm
Hmm, are you sure it wasn't 0.05mm!0.5mm of skirt clearance is bit ridiculous.
mrfxit,
Jan 22, 5:15pm
Ta for the vote ;-)
Scariest job EVER . was a PA Vauxhall 2.6 done for a brother. Total rebuild with NO new parts, just whatever I could find from the collection of parts (& there was LOTS) in the shed. Did a bit of overtime with vernier calipers / feeler gauges & micrometer gauges. Got it running fine & told him to take it easy for a week (bit of a hard driver dude aye). Car sat for that week as he was working on a demo derby car Cranked the PA up hitched on the tandom with his derby car on it & buggered off to Rotorua for the Saturday night race.
I found out on Sunday about his "test drive" & looked over the car , took it for a drive . . Well bugger me . it was running perfectly with no rattles/smoke/ leaksetc . NADA problems
mrfxit,
Jan 22, 5:28pm
Agree to a point.
Cost & time involved has a fair amount to do with "expectations" of quality of work. Well . it does at least for reasonable ppl. Example: $500 for a s/h parts rebuild compared to a $4000 full recondition. Same 4cyl common engine to same stage of remove/refit from /to car etc etc
$500 = should be good for anything from 1 to 3 years mostly trouble free running with reguler maintanence as needed
$4000 = WILL be good for anything from 3 to 10 years with general maintanence only & trouble free running with reguler maintanence as needed in the 1st 2 to 3 years
Of course with the usual proviso's of a reasonable owner driver & due care.
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