General Mechanics Question: lubed threads

[LoHo]

As I was pulling the head bolts off of Effing Bee, the tortured metal sound they made as they started coming loose got me thinking.

Those bolts are torqued pretty tightly due to their role in keeping compression. Would a fine coating of oil or grease on the threads before retorquing be a good or bad idea? I don't want friction to make the torque wrench click prematurely, and preventing frozen bolts is usually a good idea, but I am uncertain whether there is a downside and I've never seen it mentioned.

Any mechanical physicists care to comment?

[DAVINCI]

Read the manual, its says to lube those threads.

[motoman]

Hi Larry......Bolt torque is for the bolts benefit, not what its holding in place. A properly torqued bolt will stay tight, an overtighened bolt will come loose........reason being overtighened distorts the threads and will eventually work loose. Torqueing head bolts to suggested torque values also hopefully creates equal and even pressures to all of what is being torqued in place. Depending on application, bolts torqued can serve a two-fold function.

[LoHo]

Thanks Davinci, just throw the manual in my face...LOL

I hadn't read to the "reinstall" bit yet, so I will read it and will grease them up. I have done it at other times on different parts, and wasn't sure if there is a rule-of-thumb or everybody-knows for these things.

Thanks!

[LoHo]

Yeah, Moto, I stick to the torquing chart pretty closely, since snapping off one of these bolts is pretty disgusting. And for the higher torques, a lot of times I am worried about just that before I hear the reassuring "click".

On a related note, I assume that lifting the head off will tear hell out of the head gasket, and will need to be replaced. Is this one of those, "Oh, it might be okay to reuse" things, or "a competent mechanic never reuses a used gasket" sort of thing?

[DAVINCI]

I've seen threads here where some swear by re-using head gaskets. As a rule, I don't if only to keep from having to do the job over again when the gasket fails. Time is the only thing we can't replace.

[LoHo]

Since it is the original gasket, I'm sure it will shred upon lifting the head, so it is probably a no-brainer. But I have seen heads come off intact, and then I'd wonder...so I'll buy a new one and save myself another "I knew I should have done that" incident.

[natemoen]

I would change it. I will say though, I pulled my head this summer and it was the original gasket and it is still all purdy and intact (i kept it just for that ya never know moment).

[DGXSER]

If your on a really tight budget and the gasket comes off intact, it can be reused and will seal fine. But as a rule, I would recommend using a new one.

As to lubing the bolts, sounds like you already figured it out, yes, by all means, do lube the bolts as you re-install. For all the reasons you mentioned. Now I do not think I would pour oil into the hole first or anything as that will take up space the bolt needs to go into.

[TopCatGr58]

Hey there LoHo,

I do hope that you will be buying the gasket KIT from PNM or such, not just the Head Gasket from Yamaha! For just a few bucks more than the head gasket from Yamaha, you get an entire kit!

It's in the manual, but wanted to mention that the retorqueing process describes two stages for the head bolts/nuts....to IIRC 14 lbs, then up to 25 lbs. The nut on the bottom side of the FRONT of the head is only 14 lbs, don't forget that one when taking it apart.

Also the new gasket will NOT have the need for the old rubber cam chain galley sections, they are incorporated in the whole head gasket, do NOT put them in with the gasket. And of course..NO SEALANT on the head gasket, it goes on DRY!.

Also, after you get it together and running, just run it gently up to normal temps, then let it cool, and then RETORQUE the nuts.

If you do find the little offending washer wedged against the cylinder wall, you may be able to just do a Honing of the cylinders to clean it up from the scratches!? Hope it didn't ding or gouge the head much!?

T.C.

[79XS11F]

You will want to lube them with oil and if you want to be real real good you will run the correct size die down the threaded part of the studs and a tap into the nuts to clean the threads up before you assemble it.
Rob

[jetmechmarty]

Torque on the bolt stretches it. That torque changes when you apply different lubricants. Always use what is specified in your manual.

[clcorbin]

You will want to lube them with oil and if you want to be real real good you will run the correct size die down the threaded part of the studs and a tap into the nuts to clean the threads up before you assemble it.

And if you REALLY want to be good, you will use a resizing die and tap (also referred to as a "thread chaser") instead of a cutting die/tap. The resizing die/tap will push the threads back into the correct position instead of cutting off even more of the existing threads which could lead to weak threads.

[natemoen]

If you do end up needing to hone the cylinders (dont just do one, do them all at the same time) DO NOT heat cycle the head as TC first stated. You will glaze the cylinders and the rings will never seat properly. If you hone the cylinders DO NOT even start the bike till you are ready to ride it. If you are going to try and start it, be ready to ride it and if she starts GO, don't even let it warm up just go and ride it.

[cywelchjr]

If you do end up needing to hone the cylinders (dont just do one, do them all at the same time) DO NOT heat cycle the head as TC first stated. You will glaze the cylinders and the rings will never seat properly. If you hone the cylinders DO NOT even start the bike till you are ready to ride it. If you are going to try and start it, be ready to ride it and if she starts GO, don't even let it warm up just go and ride it.

+1 on the don't warm it up first. This link here gives information on how to PROPERLY break in an engine, and prevent glazing of the cylinder walls as can happen if you actually follow manufacturers recommendations.