Yanmar 2GM exhaust elbow bolts

[RichardS]

If the thread is lubricated the tightening torque should be reduced

Richard S suggests a very much lower torque ......... what you have to decide is who is correct Yanmar or Richard . Perhaps he is allowing for being well greased although he does not say.

Of course, I am talking about a thread well greased with copper grease. You know that better than most Vic. My description would give something like a 25 - 50% reduction so it sounds just about spot on.

As I, and Spryo said, this is a non-critical application and provided it is tight enough not to leak, which is easy to ascertain, it will be absolutely fine.

One day I'll explain why most manufacturers torque settings are too high and can be safely ignored in many situations .... but not all. Knowing which situations the settings can be ignored and which situations they can't takes decades of experience.

Richard

 

[Channel Sailor]

If it does not need SS then why bother using it. Visualise further down the line when it gets stuck and you need to drill it out or cut the head off. From what I understand SS can be problematic for example when over tightened or even just unlucky the threads can pick up or create a swarf that can jam the thread.

 

[webcraft]

If it does not need SS then why bother using it. Visualise further down the line when it gets stuck and you need to drill it out or cut the head off. From what I understand SS can be problematic for example when over tightened or even just unlucky the threads can pick up or create a swarf that can jam the thread.

OK, I have ordered the Yanmar original bolts.

Only one out of the three had a spring washer. Perhaps I shouldn't fit them? Are they necessary?

- W

 

[VicS]

OK, I have ordered the Yanmar original bolts.

Only one out of the three had a spring washer. Perhaps I shouldn't fit them? Are they necessary?

- W

They show washers in the diagrams in the workshop manual don't they ?

If you got it back from a professional mechanic and discovered he'd not bothered with the washers , despite them being shown in the manual, you be a bit miffed wouldn't you

 

[Spyro]

Nick, you're overthinking this. If you got the bolts out you could have just used them again. They don't need to be over tight or have spring washers. As Long as you have the correct type of crush gasket and the mating faces are good it will be fine.

 

[RichardS]

Nick, you're overthinking this. If you got the bolts out you could have just used them again. They don't need to be over tight or have spring washers. As Long as you have the correct type of crush gasket and the mating faces are good it will be fine.

Although I think the OP said that the original bolts had rounded heads so, on balance, I would change them for either stainless or steel depending upon what I had to hand.

I have a lot of stainless bolts to hand at the moment because the Series 3 restoration is approaching completion and, God forbid, I have replaced all the Land Rover bolts (imperial), mainly mild steel machine screws, with stainless steel M6 and M8 and have needed over 50 of each. It's like a giant Meccano set.

Land Rover purists will be spinning in their graves and it's probably knocked a fortune off the value ..... but there's Land Rover engineering and then there's RichardS engineering.

Richard

 

[JumbleDuck]

As a general guide Yanmar say 23 - 27Nm ( 17 - 20 lbf.ft ) for M8 when no other torque is specified in the manual.

I bought a Norbar 3/8" torque wrench for doing up Yanmar 1GM10 bolts. It's compact (so fitted in my engine bay) and has much lower limits that its 1/2" drive brute of a big brother. They come up economically on eBay.

 

[ghostlymoron]

I've always thought torque was a very crude method of measuring the clamping force which is what we're interested in.

It would be with a spring washer if that is what is normally fitted but it would be with unlubricated threads.!
It is higher than I expected but I checked with two manuals and Earlybird has found the same figure !

As a general guide Yanmar say 23 - 27Nm ( 17 - 20 lbf.ft ) for M8 when no other torque is specified in the manual

45Nm is more than I can manage comfortably with the short pattern ring spanners I normally use although within my capability with a 1/2" drive socket set and its normal tommy bar. However what I can now manage must be viewed against my now much reduced physical strength compared with a few decades ago ( Getting he skin off a rice pudding is now quite a task!)

If the thread is lubricated the tightening torque should be reduced

[table="width: 300, class: grid, align: center"]
[tr]
[td]lubricant[/td]
[td]% reduction[/td]
[/tr]
[tr]
[td]none[/td]
[td]0[/td]
[/tr]
[tr]
[td]graphite grease[/td]
[td]50 - 55[/td]
[/tr]
[tr]
[td]white grease[/td]
[td]35 -45[/td]
[/tr]
[tr]
[td]SAE 30 oil[/td]
[td]35 -45[/td]
[/tr]
[tr]
[td]SAE 40 oil[/td]
[td]30 -40[/td]
[/tr]
[/table] Source: Enginerring Toolbox

Richard S suggests a very much lower torque ......... what you have to decide is who is correct Yanmar or Richard . Perhaps he is allowing for being well greased although he does not say.

 

[ctva]

It would be with a spring washer if that is what is normally fitted but it would be with unlubricated threads.!
It is higher than I expected but I checked with two manuals and Earlybird has found the same figure !

As a general guide Yanmar say 23 - 27Nm ( 17 - 20 lbf.ft ) for M8 when no other torque is specified in the manual

45Nm is more than I can manage comfortably with the short pattern ring spanners I normally use although within my capability with a 1/2" drive socket set and its normal tommy bar. However what I can now manage must be viewed against my now much reduced physical strength compared with a few decades ago ( Getting he skin off a rice pudding is now quite a task!)

If the thread is lubricated the tightening torque should be reduced

[TABLE="class: grid, width: 300, align: center"]
[TR]
[TD]lubricant[/TD]
[TD]% reduction[/TD]
[/TR]
[TR]
[TD]none[/TD]
[TD]0[/TD]
[/TR]
[TR]
[TD]graphite grease[/TD]
[TD]50 - 55[/TD]
[/TR]
[TR]
[TD]white grease[/TD]
[TD]35 -45[/TD]
[/TR]
[TR]
[TD]SAE 30 oil[/TD]
[TD]35 -45[/TD]
[/TR]
[TR]
[TD]SAE 40 oil[/TD]
[TD]30 -40[/TD]
[/TR]
[/TABLE]
Source: Enginerring Toolbox

Richard S suggests a very much lower torque ......... what you have to decide is who is correct Yanmar or Richard . Perhaps he is allowing for being well greased although he does not say.

Where would copper grease fall on the table?

 

[BobnLesley]

... Might have difficulty getting a spanner on one of them if I use standard bolts, but will give it a try. - W

Same problem on our 3GM so replaced them with Allen-head studs; I use an aluminium high temperature grease on these and anything similar, including the faces of the adjacent exhaust-gasket

 

[simonfraser]

apologies re drift, but copper grease on car wheel nuts, same reduction ?

 

[penberth3]

apologies re drift, but copper grease on car wheel nuts, same reduction ?

Er, why copper grease on car wheel nuts?

 

[penberth3]

Like this:

Good idea, but could these be done up to the necessary torque ? (45NM)

- W

They could, the problem will be undoing them in future. Easier to round off a small hex key than a 12mm bolt head. Also, socket screws are often harder than 8.8, so drilling out won't be easy.

 

[RichardS]

Er, why copper grease on car wheel nuts?

I've been using copper grease on all car wheel nuts and on the hubs for the last 40 years, although in recent years, more often aluminium grease on the nuts and hubs for alloy wheels because it looks less messy.

Used for the same reasons that I use it on every nut and bolt on a car or boat, anti-seize and preservation of good thread quality.

Richard

 

[RichardS]

Where would copper grease fall on the table?

Copper grease is a poorer lubricant than other forms of grease so it will probably be below 35% .

Richard