| Author | Message | ||
     Steeleagle |
I've got my engine (1992 RS1200) torn apart to replace a crank and am performing due diligence in checking all the other stuff while I have it gutted. Among other things, I want to verify the wear status of the cylinders, not knowing mileage, etc. on them. HD says you need to use a torque plate to get accuracy for any bore checks. While I understand the concept, for the purposes of strictly trying to see if I might need an overbore (and therefore new pistons...which would impact my crank decision (thinking S&S)) how far off will my assessment be if I measure WITHOUT a torque plate? If a plate is the only way, a quick check tells me I'll either need to farm it out or spend $400 to buy a plate, unless there's an agricultural engineering solution for getting reasonable accuracy. I'm mechanically fearless and fiscally irresponsible, but don't REALLY want to spend money I don't need to. I know HD assumes that if you're torn down that far, you MUST be a full-tilt shop and have all their goodies, but...not so much! Anybody with experience that can guide my efforts? | ||
| Strato9r |
Hmmm..... Well, if you want a deathly accurate measurement, then yes, you want to simulate, as accurately as possible, the bore as it appears when torqued to the cases with a cylinder head installed. Now, that being said, there is already debate as to whether the steel plates that are actually the ones recommended by the factory simulate torque loading as accurately as aluminum plates. Or, how much thermal factors influence the shape of the bore. Lots to consider? You bet, but remember, the amount of distortion encountered when using torque plates is relatively small compared to the accuracy required to determine whether or not the bores are worn to the point where they should be bored oversize. Personally, if I were replacing a crank assembly, I would lean toward reboring the cylinders for a couple of reasons. First, you could order up a rotating assembly that is already balanced to the proper bobweight, and not have to worry about the weight of your original pistons requiring your new crank to be rebalanced. Second, tiny differences in stroke and rod length could drive the piston past the point of original ring travel, raising hell with the top ring land, and possibly pinching the second ring land tight enough to seize the second ring in it's groove. Uncommon, but we just had an engine in the shop that had this exact problem. Here's what I'd do if I were in your situation: Take the cylinders to a shop that has a set of torque plates, and have them set them up, and measure them with a dial bore guage. Even if the shop charges you time to check them, you are still money ahead, knowing for sure what kind of shape they are in. Folks that do this sort of thing every day will also be able to give you a definate size that the cylinders will have to be bored to if nessesary, making ordering parts easy for you. | ||
| Pammy |
Farm it out. I agree with Strat. | ||
| Cvc |
I agree but would add who would you take them to to have them bored? They would be the one I would use to measure and some times will credit what they charge for measuring if they can do the work. CV | ||
| Bluzm2 |
Send um to Pammy! | ||
| Pammy |
Well you have to find someone who has the proper torque plates. Paramount. Then you want to make sure this someone has a good reputation. Word of mouth is best. Advertising should just get you interested. (after all the entity doing the advertising wants your business at all costs) Personal experience should sell you. You need to decide what your budget is. Project creep is common. Talk to others who have had your problem. Hear all the issues that can arise and be prepared for them. Don't do it half-assed. I am not talking fastest, biggest, highest tech. I mean if it should be replaced(worn), replace it. Projects are always fun and interesting....the first time. If you have to do it twice or more...then it is just a big old burden. Costly and a hard lesson learned. | ||
| Steeleagle |
OK, I hear everyone say that they should be in torque plates to accurately measure bores, and I’m OK with that, although Strato9r makes a good point in that even in torque plates the cylinders won’t have the same profile as they will when they’re warmed up/hot from actual combustion, so how much error does THAT induce? I most assuredly want to doing this right, but: a) I don’t want to spend money for service I’m perfectly capable of performing myself, given good guidance from experts with experience. b) I have more faith in my abilities than I would a (currently) unknown mechanic who may not have the same vested interest as I do. c) I want to establish whether my parts are still in good shape and therefore reusable. Harley says I can measure bores in a torque plate, but says you can’t measure pistons, so how would a reputable shop do that to confirm moving parts and fixed parts mate? In other words, how do I know if the pistons are worn, regardless of bore condition? Re; Budget: There’s no interest in hop-ups, big-bore, etc. IF I have to replace jugs, I’d probably go with stock bore replacements, stock bore pistons, etc. Again, I’m not opposed to investing in what NEEDS to be replaced or services I am not equipped to perform. For giggles and reference, here are my measurements of the bores (WITHOUT the use of a torque plate): Front bore: F-R / L-R Top: 3.4982” / 3.4972” Mid: 3.4977” / 3.4975” Bot: 3.4966” / 3.4982” Rear bore: F-R / L-R Top: 3.4982” / 3.4976” Mid: 3.4976” / 3.4976” Bot: 3.4962” / 3.4977” I measured with a dial bore gauge with resolution to .0001”, so I’m comfortable with the accuracy. I can also provide pix of the current state of pistons/bores if that would provide additional insight. Pammy: What is a "proper" torque plate and what's a typical fee for the whole measurement process? I’m an mechanical engineer and admittedly will probably over-think this and question everything, but that’s what I do, so don’t take ANY of my comments as questioning expertise, experience, etc. for those that have established both. Half-assed isn't in my vocabulary. Slow and meticulous is a curse I have. It’s just that until I’m convinced of the proper path to follow, I’ll probably be appearing as either a moron or an a-hole…maybe both. Thanks to all for the input. Keep it coming. | ||
| Strato9r |
Measuring pistons is something that should be done anytime they are out of their bores, and literally every piston that comes into our shop is measured to make sure that we can establish how much piston skirt or bore wear has occurred, or in the case of new pistons, if they were damaged in shipping (2 pistons in different sets this week alone!). In the case of pistons with coated skirts, many manufacturers will insist that the bores be finished at the recommended dimension, and to not measure the skirt. For your sake, I see no reason for not measuring the piston skirt at 90 degrees from the pin, at the bottom of the skirt itself. This measurement, subtracted from the measurement of the smallest section of the bore, will give you a minimum clearance of piston skirt to an unstressed bore. Compare that with the measurement of the bore at approximately one and three quarters of an inch from the top of the bore, (essensially the highest point the piston skirt will travel throughout it's stroke). This will give you a pretty decent ballpark idea of bore wear, as it relates to skirt clearance. Honestly, if there are no scratches or scuffs in the bore, there is no discernable ridge that has formed at the top of ring travel, and there are no unusual ring wear patterns, the bores are quite likely servicable, as long as the piston skirts show no signs of collapse, and the pin bores and ring lands are within spec. I totally understand that you are probably as capable as many shop employees are at determining whether or not your stuff is reusable, and hey, everyone has to work within a budget. That being said, check out the local shops, and get an idea of who is willing to discuss your situation, and who seems to be inclined to blow smoke up your butt. If you can't find anyone in your area, there are any number of BadWeb supporters who would be willing to help out. For what it's worth, given the measurements that you got from your bores, there should be no reason to replace the jugs on your motor even if you go with new pistons; .010" or .020" would do it easily. | ||
| Pammy |
I most assuredly want to doing this right, Then farm it out to an expert in your area. but: a) I don’t want to spend money for service I’m perfectly capable You are assuredly not perfectly capable of boring and honing your own cylinders if that is not your profession (tools, experience, etc...) of performing myself, given good guidance from experts with experience. b) I have more faith in my abilitiesI think most of us have this affliction but you are better off realizing your limitations as are we all. than I would a (currently) unknown mechanic who may not have the same vested interest as I do. A professional will have a vested interest. A good reputation is extremely hard to come by and considerably more valuable than one motor. c) I want to establish whether my parts are still in good shape and therefore reusable. The cylinders would have to be trashed and or bored to the limit for them to be considered unusable. I would say that the rings, at least, require replacement. The pistons may have to be replaced due to the need for an overbore. Proper torque plates would be what a professional would use. Not something that "will work" or something to make due. Proper tool for the job. The cost for just measuring your cylinders should be somewhere between $30 and $40 bucks. If you choose to use coated pistons, the machinist uses a final bore size. If they are not coated a piston to cylinder wall clearance is recommended by the piston mfg. The builder uses his/her discretion (within mfg parameters) related to end user application. I know you have heard this before. The only stupid question is the one you don't ask. | ||
| Fast1075 |
I can personally attest to Pammy and Wes and crew as being one of the very best shops in the business...period. | ||
| Blake |
You speak truth. There are none better. | ||
| Datsaxman |
Steeleagle, New OS pistons and a fresh bore are mandatory. Good practice to replace lower cost/smaller/higher wear items when you are doing major work. We still drill that into engineering majors...doesn't always take I guess. Planning to check the oil to see if that has some life left in it? Save the $30 - $40 Pammy wants (!!) for a measurement that can only tell you what you should already know and do the job right the first time. Pammy, the post is about MEASURING. The OP is not contemplating hogging out his own cylinders. | ||
| Pammy |
Pammy wasn't wanting anything from the gentleman. I specifically said he should find someone in his area. I agree that he should not send them to me. Again, I never suggested that he should. I was just guesstimating the cost for him, verses the $400. he mentioned for torque plates. If he replaces the pistons as you suggest, someone is going to have to "hog out" the cylinders and that someone should have the proper tools. Once again, I suggest he find someone reputable in his area. I believe I checked before and that certainly wouldn't be me. I was only giving prudent advice based on many years experience. |
