| Author | Message | ||
     Foximus |
So I'm tearing down my motor in a full top end project (for the most part...) Because of neglecting previous owners, the front cylinder burns oil like you would not believe, and it basically just leaks out of everywhere else on the damn bike.... So... while I'm at it I bought 07 screamin eagle heads and some matching black cylinders from a m2 (s2?) Well I tear down the motor today (much thanks to Buellistic for some hints and tips over the phone)... First stupid thing i see... what do you think? they are using 883 head gaskets. 1/4" all the way around burnt to a crisp. And of coarse they fixed this motor with mismatching cylinders... one being the original silver cylinder (I assume orriginal) then the rear cylinder replaced with a black w/ highlighted fins... naturally there are mismatching pistons inside, however both actually match up to 3.465" ~+/- 0.005" Now that being said... the rear cylinder which was firing fine, has tons of vertical score marks. The front cylinder which was burning oil like a drink, has perfect hone score marks still, and there is not a single scratch or score anywhere on the piston and the oiler ring looks fine? Opinions? | ||
| Foximus |
a few build pictures here, its easier than sizing them all down and uploading them a second time... http://www.facebook.com/album.php?aid=2721118&id=5 115131&saved&forceClose=1 | ||
| Foximus |
have everything doing a cycle in the parts washer right now.... | ||
| Jramsey |
+/- .005"? don't know what your measuring with, hope thats a typo! .0005" would be more like it. The "rule of thumb" is .001" for every inch of bore Dia. 3.465 dia. = .0035" clearance using telescoping gauges and micrometers. | ||
| Foximus |
between the two i meant. | ||
| Sportyeric |
I'd guess that one piston is 5 thou over. You'd want to check your new cylinders for straightness and roundness and decide from there if you will be getting them bored five thou over, in which case you may have one piston that you can re-use. | ||
| Foximus |
Well the two pistons are almost dead same.... its the cylinders i'm having trouble gettin a good measure on. However I dont have the best caliper either.... Any thoughts on why i would be blowing that much oil without having badly damaged oil ring or scared cylinder? | ||
| Natexlh1000 |
Valve guide seals? | ||
| Buellbozo |
There's no way to accurately measure cylinder bores with calipers. Expensive dial reading bore guages are nice, but simple telescope guages and a micrometer work perfectly well. Check the current thread on Torque Plates. Remember that the ".0035" clearance quoted above is a diameter measurement. That means ".0017-.0018" per side piston to wall clearance. | ||
| Foximus |
Just ordered .005" over HD pistons. Might have been better off going with some forged Hurricane pistons, but meh... couldnt beat the price and reliability of the HD pistons. Cylinders are at the machine shop. | ||
| Midnight_rider |
most machine shops i ever seen had to have piston with cylinder to get side clearance are they boring without piston? | ||
| Jsracer |
3.465" is not a standard HD/Buell size. Stock 1200 bore is 3.497". My guess is you're measuring the crown, above the rings. That's not where it matters. Measure about half an inch up the skirts. Also, lose the caliper, get a good tenths reading micrometer (.0001 resolution). You need that much resolution. .0035" is way too much clearance for any piston in a stock cylinder. In a full steel or cast iron cylinder, with a forged piston, sure, but you don't want that in a stock cylinder. The correct clearance number comes from the piston manufacturer, but .0020 to .0030 is typical for a forged piston and .0006 to .0015 is typical for a cast piston. If you bought stock pistons, they're cast. Always measure the piston diameter and the bore diameter using the same micrometer. The same outside micrometer you use on the piston should be used to zero the bore gauge or to measure the telescoping gauge. In addition to using the right tools, and torque plates, and measuring the right places, there's a lot of technique to measuring pistons and bores, to get accurate and repeatable numbers. If you're not experienced at this, it's best to get some help from someone who is. One other thing: cross hatch still showing is very often NOT an indicator that things are good, in fact it generally means the opposite. Look around the bore, are there places that have cross hatch and places that don't? If that's the case, and it usually is, it means the cylinder is most likely out of round and there are places where the rings aren't touching the cylinder walls. That's why the cross hatch is still there. This is very, very common in Harley cylinders. It's also the reason why torque plates are so important. | ||
| Foximus |
A) my caliper is good enough for the work I do. Since I only ever assembly my own motors, and never do the bore work myself its not anything hugely important to me. B) your right, I did measure at the crown, I did not even think of that last night. My mistake there. C) I ordered the pistons directly to the machine shop, so he will bore them when they arrive. D) upon closer inspection today, the cylinders and pistons were setup so loose there must have been a huge amount of piston slap/rock, because the oil ring was compressed all the way in, and did not expand back out when i pulled it. I did not notice this last night. It had .0045 clearence. Overall... this is what you get when MMI idiots build something. (Message edited by foximus on January 18, 2011) | ||
| Buellistic |
Looks like technicians say if the the PISTON is 5 over piston the cylinder bore will have to be so big by just scanning my FACTORY SERVICE MANUAL ... Being OLD SCHOOL "i" want to KNOW how BIG the piston is and "i" will deside how much piston/cylinder wall clearance "i" want to run !!! "AND" ring gap is very important as is how you stager the ring gaps which has a bearing on how the piston tilts on the power stroke ... "The Devil is in the DETAILS !!!" (Message edited by buellistic on January 18, 2011) | ||
| Blake |
>>> "AND" ring gap is very important as is how you stagger the ring gaps which has a bearing on how the piston tilts on the power stroke ... More info please. I wanna learn. | ||
| Foximus |
Staggering the ring, is where you leave the gap. either 180* from each other or 90* from each other. 180* places ring forces only in 1 direction, 90* would place outward forces in 2 directions. I believe that is what he is referencing to. | ||
| Foximus |
And yes, I agree Buellistic, I tell the machinist what gap to run, however I do trust him in his measurements and followthrough as I have used him for quite a while. | ||
| Rick_a |
Most of the bad work I've seen is done by the guy someone knows; friend of a friend that does work cheap type deals...or owner induced idiocy. A reputable shop stands behind their work, and they typically don't let newbs tackle engine work until they've proven themselves. The ring gap [indexing] is important for initial running. They pretty much go where they want to after that. (Message edited by Rick_A on January 18, 2011) | ||
| Jramsey |
Jsracer, you evidently missed the quotation mark on my "rule of thumb" remark. The OP is measuring with a caliper of unknown quality and with questionable technique which makes no difference other then he can get a rough measure to tell whether std. bore or oversize. I've bored/honed hundreds of blocks/cylinders and always go by piston mfg. specs. unless requested otherwise. | ||
| Blake |
>>> 180* places ring forces only in 1 direction, 90* would place outward forces in 2 directions. I'm not sure what you are talking about. My understanding is that the pressure of combustion tends to expand the rings, pushing them against the cylinder wall while also pushing the rings down against the lower face of the ring groove. I can see a very small force due to the gap that would tend to push the ring in the direction opposite the gap, but that is very much less force than what is pushing all the rest of the ring against the cylinder wall, so I don't see it being a factor. | ||
| Jramsey |
Dykes or more pc today gas port/head land rings seal with combustion forces. ( not always or limited to the top compression). STD and Keystone type rings don't work that way for practical purposes. Ring end gap placement is normally determined by the amount of rings per bore. 2 strokes engines the end gaps are located with pins to keep the rings from rotating on the piston and snagging a port in the cylinder. 4 stroke rings ( top/scraper/oil)as a general rule should be installed with the end gaps 120 degrees apart(provided 3 ring piston) with the 3 piece oil control ring upper,lower end gaps 180 apart with none of the end gaps inline with the thrust face of the the piston. | ||
| Foximus |
yes, it seals with combustion gasses blake, however a ring can only open up perpendicular to the slice of the ring. So no matter if it is it's own spring force or the combustion, it only opens in one direction... | ||
| Steeleagle |
Per the HD manual on measuring pistons: "Because of their complex shape, the pistons cannot be accurately measured with standard measuring instruments. ...They are barrel-shaped when viewed from the side. This barrel shape is not symmetrical" So....how are we measuring and matching pistons to bores? Or could this statement just be a marketing scheme for their factory service centers? I haven't measured anything on my project yet and am more curious and perplexed as these discussions go on. In my case I'm planning to measure bores w/o torque plates (bore gauge) to see if it's in the park for standard bore of 3.4978. Pistons? Right now I need advice. My project will be a little slower moving than the OPs and I'm all about learning before I leap. | ||
| Fast1075 |
Rings do not "hold" the piston in the bore. That job is for the piston skirt. Proper clearance assures the piston does not rock in the bore. The idea of spacing the rings make a more convoluted or labrynth path for combustion gasses that make it past the ring end gap to get to the crankcase. In reality the gaps move around during operation. Ring gap is determined by bore size and ring material type in conjunction with target cylinder temperatures. A "street" motor can run a lot tighter gap than a race motor...I found on my nitrous motors the top ring especially needed a lot of ring gap. The three piece rail type oil ring is made very thin to scrape oil effectively. Because it is thin, it exerts very little pressure on the cylinder on it's own. The expander is effectively a "spring" to help with the tension. When fitting rings, good attention needs to be paid to having the ends parallel in both axis (either use a gapping tool or be very deliberate when hand cutting...check often and go slow). Be sure to deburr the ends of the ring after gapping...a burr will damage both the ring land and cylinder wall. | ||
| Rick_a |
Pistons are measured according to the manufacturer's recommendation. For OEM, it's in the service manual, for aftermarket, it's in the instructions. The service manual has the piston oversizes and their corresponding bore sizes if you're going OEM, IIRC. | ||
| Steeleagle |
Service manual for HD: Standard bore upper wear limit with their standard pistons is 3.5008" before you need to go to 0.005" over, and they require a finish bore (after hone) of 3.502" BORE diameter for 0.005" over pistons. No actual piston sizing (actual measurements) given, other than the "can't be done" statement in my previous post. Apparently for HD it's a "trust us and do what we say" mentality when it comes to mating pistons with cylinders. Seems wacky, since I could have a worn piston and OK bore, resulting in unacceptable slop, but have no way to "officially" measure it (since I can't measure their pistons), according to the service manual. Am I missing something? | ||
| Foximus |
Just finished welding and drilling my motormount to fit the screaming eagle heads. Still just waiting on pistons and bore. | ||
| Rick_a |
You could have just bought one of these. (Message edited by Rick_A on January 21, 2011) | ||
| Foximus |
coulda also saved a decent chunk of change... if it dont break... it dont break. If it does... I'll buy one. ;] | ||
| Fast1075 |
Just make sure the mount surfaces are absolutely parallel in both axis or you will be chasing broken mount bolts forever. |
