molydisulfide grease? addendum

[RobertWichert]

In general, torque values are given with guidance for lubrication, or not. The manual is supposed to be consistent, that is, if it says to lubricate the threads then the torque value is for lubricated threads. Having been involved in providing torque values and torque sequences for longer than I care to contemplate, I have found that it is more likely to damage the connection by NOT lubricating it than by lubricating it. Galling is bad. Very bad. While it is quite true that a lubricated bolted connection puts more compressive stress on the connection than an un-lubricated connection, the number of threads being used usually makes thread stress less of an issue than stress on the bolt, which is most likely to fail. An exception is dissimilar materials, of course, and a steel bolt into an aluminum casting puts the aluminum threads at risk. If they are used, or worse, they are at great risk. That's why God made Heli-Coils, I guess. I personally believe that everything should be lubricated during assembly if the assembly is important to function or safety. Even Loktite is a decent lubricant. The biggest error band on torque-to-stress tables comes from dry threads where extremely small imperfections in the threads or in the washers, etc. can cause wide swings in compressive stress on the connection. Here is what Fel-Pro says for all installations: Lightly coat bolt threads and the underside of the bolt heads with motor oil. When they enter the water jackets of an engine, bolt threads should be coated with a non-hardening automotive sealer to prevent leakage. Refer to the manufacturer s service manual or examine the engine to determine where the bolt holes lead. Lee, I certainly agree with your approach, but I would not lower the torque value. In most cases a bolted connection will relax as the imperfections yield. This is normal and expected. For this reason a lower torque value can lead to a leaky or loose connection more likely than a lubricated connection will lead to thread failure. Galling is actually more risky than torque, in my experience. Robert P. Wichert P.Eng +1 916 966 9060 FAX +1 916 966 9068 ========================================================

On 8/23/2010 10:15 AM, Lee Dodge wrote: A word of warning. Lubricating threads is a procedure that must be approached carefully. For instance some torque readings specify that NO lubrication be used for the reason that the factory determined the torque necessary to provide a pressure on a gasket with clean bare metal threads. If you were to apply the same torque level with lubricated threads the actual pressure on the gasket would be greater (as would the shearing aka stripping load on the threads. Not good) Even the bolt head interface needs the same treatment as it's frictional load is additive. I admit to wanting to lubricate everything as a preservation measure especially since I work a lot with older often well used bikes. It has been my experience that this type of warning or clearly specified thread treatment procedure is not often given or available for guys like us. I've encountered cases where there is no factory manual either existing or available and if the parts are rare or very expensive I choose to err on the side of lubrication and less torque and wait to see if it holds. Lee --- On [b]Mon, 8/23/10, Jeff Khoury [i]jeff@...[/i][/b] wrote: From: Jeff Khoury jeff@... Subject: Re: [DSN_KLR650] Molydisulfide grease? To: "mark ward" nomad59@... Cc: "List KLR" DSN_KLR650@yahoogroups.com Date: Monday, August 23, 2010, 9:10 AM A quick google search yields many references to using moly grease on head bolts. I've never done it, although I might now. -Jeff Khoury ----- Original Message ----- From: "mark ward" nomad59@... To: "List KLR" DSN_KLR650@yahoogroups.com Sent: Monday, August 23, 2010 9:05:06 AM GMT -08:00 US/Canada Pacific Subject: [DSN_KLR650] Molydisulfide grease? Hey Jeff & all the clymere book, says to use Molydisulfide grease on the bolt threads and head seat when reinstalling after valve check. it's Only only time, I've, seen anything like this mentioned. INPUT?????