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Post by jloi on Dec 23, 2020 2:12:20 GMT -5
Brent; is there such a thing as resurfacing the mating surfaces to a finer tolerance ?
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Post by 190mech on Dec 23, 2020 5:09:05 GMT -5
Lubing threads does greatly increase torque..I remember David Vizzard did some tests on SB Chevy head bolts and there was quite a difference.We have 2 different aircraft propellers that use the same thread studs for attachment to the crank flange,one specs dry threads(75 ft lb),the other specs graphite grease and 45-50 ft lb..I bet they both have the same clamping pressure..
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Post by Lucass2T on Dec 23, 2020 6:27:05 GMT -5
Whats your view on lubing threads John? For example should one lube head bolts or put copper grease on lug nuts?
When threads are brand new or super clean I rarely lube them unless stated otherwise. Or when it's two different metals touching each other (steel bolts in aluminum). Im all for lubing threads that don't need a specific torque spec or that are a bit dirty or damaged. Also I put copper grease on lug nuts no matter what.
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Post by oldgeek on Dec 23, 2020 6:31:03 GMT -5
I feel like the guy that commented about torqueing could be right, but only if you were grossly over torqueing the studs. According to your stated torqueing process I dont see how you could be over torqueing the studs. I guess giving his recommendations a try costs nothing, so......
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pewpew
Scoot Enthusiast
Posts: 254
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Post by pewpew on Dec 23, 2020 7:39:36 GMT -5
I took the cylinder head off to see what wasn't sealing. Not totally sure. My best guess right now is that no stud o-ring seal failed, but maybe the bore o-ring allowed combustion byproducts into the coolant. The bottom area on the head and cylinder doesn't show the same evidence of contact as other areas and there's some gas/oil there upon disassembly. The o-ring appears to have a clear seal there where it faces the bore, but not where it faces the coolant. The bore seal looks "iffy" in other spots. Maybe the o-ring area could get combustion pressure in it and the seal to the water jacket fails in a different area? No remnants of combustion stuff in the groove though. It's not clear that there's a seal between the stud and bore area in a couple of spots, but there is no combustion crud in the o-ring grooves and the OD of the o-rings look sealed. I checked the head and cylinder deck with a straight edge and they seem fine. For now, I'm planning to reinstall the head and see how it does unless someone else sees something. On the comments for the video that I added today, someone is telling me that they have installed 20 TPR kits for customers and only 1 had a head sealing issue so I'm doing something wrong. He thinks that is over-torqueing and re-torqueing. So first off, he says to always use the low side of a spec. So if it says 11-12Nm, go with 11Nm. Then he says to never re-torque. He says the manufacturer wanted the torque just as it is when installed and anything after over-torques it. When the metal expands and contracts it needs the gaskets to have the tension as initially set and re-torqueing will make everything too tight and cause problems. He goes on about it being aluminum and tons of pressure. His suggestion is to torque to 11Nm (12.5 is what I use) and then never touch them again. Re-tq was standard for big V8s and such. Some gasket types like copper and cometic didn't even wanna seal until re-torque in some cases. He says those have big torque specs and they can take it, the scoot doesn't. I'd say yeah, but the scoot also isn't torqued to 75ft-lb, so it's all relative. I never say I know everything and we know I screw up plenty, so I looked around. It appears to be standard practice for the MX 2T crowd too, at least based on forum posts. Can't find Polini, Malossi, TPR, Stage6 mentioning anything about it. To be clear, here is the re-torque procedure that I've been using... 1) Install and torque within spec. 2) Take a short ride and get coolant and CHT up to operating range. Not just warming up on the stand. 3) Let it cool off to room temp. 4) Go over the cylinder nuts again at the same torque spec used during install. Now, #4 is not really the correct way to do a re-torque to my understanding. It is what I've come to do on these LC scoots. What I believe to be the best method for a re-torque is to loosen one nut, then torque it to spec again. Continue till all fasteners are done. Loosening is done because it will take a certain amount of force to overcome the tension/friction of the mating surfaces and the threads and loosening and re-torqueing from there should deliver a torque closer to spec. For the same reason, I try to reach torque with a torque wrench on a long pull if possible instead of ratcheting short pulls. The reason that I don't loosen them is because it seemed like I was having more trouble with leaks in the past when I loosened even 1 fastener at a time. Could be in my head. Either way, the nuts pretty much always require part of a turn as I do it after a heat cycle. I also use motor oil on the threads, which is commonly specified in some applications (or companies like ARP will suggest using their specific products) but I've never seen it stated for scoots. I like to have clean threads as well so I tend to run a chaser over used studs and nuts. It could be that the lube causes over-tightening, but that's been common practice on scoots for a long time for me. May be one of those times when trying to do it "right" is wrong. When i first installed my kit, i had to use sealant on the gasket because it wouldnt seal otherwise.
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Post by 90GTVert on Dec 23, 2020 8:41:57 GMT -5
Brent; is there such a thing as resurfacing the mating surfaces to a finer tolerance ? If you look up RA or RMS surface finishes, you can find a lot of info on it. I think it would be tough for me to accurately reproduce anything very specific.
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Post by 90GTVert on Dec 23, 2020 9:09:27 GMT -5
I feel like the guy that commented about torqueing could be right, but only if you were grossly over torqueing the studs. According to your stated torqueing process I dont see how you could be over torqueing the studs. I guess giving his recommendations a try costs nothing, so...... I don't agree with everything he's saying. I can see how too much torque could be causing my heads to crack those little ridges though. I'm willing to not lube the threads and see if anything changes. In my defense of lube, I figured a little extra torque without as much risk of spinning the stud in the case is not a bad thing on initial torque. I don't use lube on re-torque, so it ends up at a spec closer to no lube, though I guess some oil lingers. I don't know that I'm willing to not re-torque. The idea of re-torqueing has been to deal with settling gaskets. You can look this up in sources like Engine Builder or Hot Rod magazine. The reason that it is now less common to find recommendations for re-torqueing in the automotive world is that they use different gasket materials than long ago. We don't really have that benefit. They've got multi-layer steel, copper, coated, layered, sealing lines around passages... We're still on putting cereal boxes under our cylinders and soda cans under the head. In automotive, they also tend to have the benefit of only one moving part, because the block is essentially one piece where we have a head mating to a cylinder and a cylinder mating to cases (and maybe a two part head) all at the same time with the same fasteners. Still, you will find in the automotive world that some gasket manufacturers do specify re-torque. I can tell you from using different gaskets, thicknesses, sealants, spacers and so on that you can see where it is really effective to re-torque and that it does indeed vary by application. Not to mention, what is the likelihood that anyone is even thinking about stud stretch and how much fasteners can vary and affect the overall picture? Unfortunately, I don't have faith in scooter parts manufacturers to provide greatly detailed instructions that worry about things like re-torqueing. They don't even ever specify dry, lubed or what lube on any torque specs that I recall and that's pretty commonplace. It irritates me. I know that some people don't even think a torque wrench is needed for a cylinder kit installation, but I'm one of those weirdos that would follow a known working set of guidelines with torque specs, lube or not, and so on because it's not that hard and it can save headaches.
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Post by repherence2 on Dec 23, 2020 10:37:38 GMT -5
Brent; is there such a thing as resurfacing the mating surfaces to a finer tolerance ? In my craft, any surface sealed with a gasket or o-ring should be RHR (rms) 63. O-ring seals can hold in excess of 4500psi hydrostatic pressure. For fluid/steam system valves with metal seats and discs our surface requirement was 16 microinches. Surface finish is dependent on application.
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Post by repherence2 on Dec 23, 2020 11:06:29 GMT -5
Lubing threads does greatly increase torque..I remember David Vizzard did some tests on SB Chevy head bolts and there was quite a difference.We have 2 different aircraft propellers that use the same thread studs for attachment to the crank flange,one specs dry threads(75 ft lb),the other specs graphite grease and 45-50 ft lb..I bet they both have the same clamping pressure.. We have a retention tank cover that had similar torque specs in regards to the specified torque with lube (colloidal graphite) or no thread lube. As far as other fit ups, we use thread lubricant on all fasteners. Colloidal Graphite in Isoprpanol for steam and super hot water systems. Molykote for valve, flange, and foundation fasteners. Tourmalene sea water grease for fasteners exposed to sea water because Molykote hardens up when exposed to sea water. We lube threads and the spot face of the bolt head and the spot face of the nut. Spot face lube is to help overcome friction during tourquing. We torque to 3000 regularly and up to 50,000 for some applications. The Navee makes sure there is thread lube, the inspector has to document it and watch workers apply it. Navee has done studies and testing in regards to clamping and bolt tensioning. For torque less than 1000 ft-lb we use dial torque wrenches. When its time to retorque joints/flanges that use rubber or garlock (paper) gaskets we pull torque on the fasteners in the star pattern until final torque spec is achieved. Most soft gaskets will "relax" so we usually have to check torque after 24 hours and then 72 hours later. The process continues until the torque stabilizes and none of the fasteners turn at the specified torque. The system will not be pressurized for testing until the gasket is "stabilized". Only spiral wound flexatalic gaskets are not retorqued, the criteria for clamping with those gaskets is based on crush/compression.
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Post by oldgeek on Dec 23, 2020 11:41:07 GMT -5
..........I don't know that I'm willing to not re-torque. The idea of re-torqueing has been to deal with settling gaskets. You can look this up in sources like Engine Builder or Hot Rod magazine. The reason that it is now less common to find recommendations for re-torqueing in the automotive world is that they use different gasket materials than long ago. We don't really have that benefit. They've got multi-layer steel, copper, coated, layered, sealing lines around passages... We're still on putting cereal boxes under our cylinders and soda cans under the head. In automotive, they also tend to have the benefit of only one moving part, because the block is essentially one piece where we have a head mating to a cylinder and a cylinder mating to cases (and maybe a two part head) all at the same time with the same fasteners. Still, you will find in the automotive world that some gasket manufacturers do specify re-torque. I can tell you from using different gaskets, thicknesses, sealants, spacers and so on that you can see where it is really effective to re-torque and that it does indeed vary by application. Not to mention, what is the likelihood that anyone is even thinking about stud stretch and how much fasteners can vary and affect the overall picture? Another point to ponder is aluminum has nearly twice the thermal expansion of steel. 1st torque and heat cycle, expansion crushes gaskets. Retorque then heat cycle again, things get really tight because gaskets have already crushed. Now it is to tight like he mentioned? We are used to working with steel cylinders, so commenter may have a valid point. Just a thought.
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Post by captincvmn on Dec 23, 2020 12:29:55 GMT -5
I’ve been told, although I’ve never verified it in writing, that oiling/greasing threads yields a much different clamping pressure than dry threads. I’ve also been told that due to NeverSeize’s properties it does NOT change torque ratings on fasteners vs lubricants.
Anybody else hear similar things about NeverSeize?
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Post by 90GTVert on Dec 23, 2020 12:52:14 GMT -5
Another point to ponder is aluminum has nearly twice the thermal expansion of steel. 1st torque and heat cycle, expansion crushes gaskets. Retorque then heat cycle again, things get really tight because gaskets have already crushed. Now it is to tight like he mentioned? We are used to working with steel cylinders, so commenter may have a valid point. Just a thought. Aluminum distorts more than steel from expansion AND from torque. I read that aluminum jugs rely on the studs/bolts more than iron, because they lack the dimensional stability to do the job alone. That could take the argument either way in my mind, but I would think of that as telling me to make sure the studs and nuts are at the right spec so they can help the aluminum rather than worrying so much about what the aluminum does. It gets weird though, because aluminum will distort enough that it really needs to use torque plates when bored or honed (often done on iron too) so the bore is concentric and shaped how you want it once torqued. So does that mean that we want it to stay how it is initially set or how it will end up after settling? My understanding is still that this comes down to gaskets and how they settle, so that tells me that re-torqueing may be necessary. If it is all about what an aluminum cylinder or head is doing, then regardless of the gasket material, you would never change procedures or specs. It's very clear that that is not the case, pretty much in any field other than scooters where people seem to happily do it close enough. If you are considering aluminum expansion and contraction with heating and cooling as the primary factor, then shouldn't it be unnecessary to re-tq even with just an aluminum head (and cases)? The cases don't see much heat, but the head is going to be the hottest chunk of metal in the equation and should experience the greatest thermal deformation. I can definitely find you motorcycle service manuals that specify a re-torque procedure for engines with aluminum heads. I probably can for aluminum cylinders, but TBH I'm not certain which bikes have aluminum jugs and if it's modern then you run into potentially improved gasketing which then doesn't answer anything about re-tq for us.
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Post by repherence2 on Dec 23, 2020 12:52:51 GMT -5
On the topic of thermal expansion:
From the pics of the cylinder and the head, it looks to me that it leaked in the area of the exhaust port. In the corresponding location on the cylinder head there are 2 coolant ports. It seems possible that there is a differential in thermal expansion in that region.
I can also see what appears to be some sealant residue on the head o-ring groove near the 2 coolant ports. The residue is on the outter wall of the o-ring groove. I was taught that the groove wall opposite of the pressure is the important sealing surface of the o-ring groove. Outter groove wall and the top of the cylinder would be the critical sealing surfaces.
I suspect it was a combination of things. Some sealant may have gotten on the o-ring during installation. Initially it will seal when the sealant cures. However, from the dynamic pressure on the inside of the bore, as well as the thermal expansion/ contraction of the bore and head, i can see it being possible the sealant no longer adhering overtime and springing a leak. Once the sealant is no longer tightly adherent to the surfaces, it becomes a potential leak path.
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Post by 90GTVert on Dec 23, 2020 13:08:05 GMT -5
Some sealant may have gotten on the o-ring during installation. Initially it will seal when the sealant cures. However, from the dynamic pressure on the inside of the bore, as well as the thermal expansion/ contraction of the bore and head, i can see it being possible the sealant no longer adhering overtime and springing a leak. Once the sealant is no longer tightly adherent to the surfaces, it becomes a potential leak path. I sprayed high tack on the bore o-ring this time around, because it did not want to stay in the groove otherwise. It's a reddish color, so that should be what you're seeing. Otherwise I normally use Mobil 1 grease lightly on o-rings, which is a similar color, but not this time because of the high tack. There's no other sealant to get on anything, because I don't use anything else.
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Post by repherence2 on Dec 23, 2020 13:21:03 GMT -5
I’ve been told, although I’ve never verified it in writing, that oiling/greasing threads yields a much different clamping pressure than dry threads. I’ve also been told that due to NeverSeize’s properties it does NOT change torque ratings on fasteners vs lubricants. Anybody else hear similar things about NeverSeize? Fasteners that are not lubricated tend to require more torque because of the frictional forces on the threads and the spotfaces of the nut or the bottom of the bolt head. In my craft, i have seen the spot face on nuts galled. When this occurs, you can attain the torque spec, but because of the friction on the spot face, the clamping force or proper bolt stretch is Not achieved. Corrosion Resistant Steel, monel, and k-monel fasteners require thread lube in my line of work. If not, those fasteners will gall and lock up from torquing/untorqing. Normal steel fasteners, we use molykote as lube and to prevent the fasteners from locking up from corrosion/rust. Steel on steel will gall too, depending on the nut and bolt/stud hardness. In the end, clamping force is dependent on bolt/stud stretch. Torque refers to the rotational force applied to the fastener. Normally you can assume that at a specific torque, a bolt/stud will stretch to the proper spec. However, friction can affect torque. The threads on a nut or a bolt is basically a cylindrical wedge. Torque correlates to the amount of force applied to the wedge to achieve the desired bolt stretch.
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