Cranckcases bolts grade/antiseize

[Artefact]

Hi

I'm about to reassemble my engine and I will replace the crankcases bolts. The question is: What grade should I use? 8.8, 10.8 or 12.8? Also,should I put anti seize on torqued bolts? If so, should I lower the torque value to compensate?

Thanks guys

[jetmechmarty]

Torque values are for clean, dry threads unless otherwise specified. You should be able to find a machinist's manual that tells you how much to lower the setting on your wrench. You are correct in assuming the value will change.

I'll let someone else make the call on the bolts.

[Artefact]

I have read 15-20% torque reduction

[jetmechmarty]

I have read 15-20% torque reduction

More like 25%. Try these.

http://www.antiseize.com/PDFs/torque_specifications.pdf

http://www.engineersedge.com/material_science/antiseize_compound_application_review_13389.htm

[Artefact]

Ok but, would you use antiseize?

[jetmechmarty]

Ok but, would you use antiseize?

Maybe. With aluminum alloy cases and steel bolts, you're going to have galvanic corrosion whenever an electrolyte (moisture) is present. The aluminum is going to give elections to the steel. The cases corrode rather than the bolts. Environment has a lot to do with it. If the bolts you pulled had white powder on them, then that's what happened.

If you use anti-seize compound, choose carefully. Some combinations of metals/anti-seize are not recommended. I use anti-seize often.

[jetmechmarty]

I believe the torque spec has more to do with the threads in the case than the bolts. Does that help? 8.8 might even be overkill.

[donebysunday]

News

to me this reduction in torque value when anti-seize is used is new to me. I always applied the listed torque and never have had any problem.
One thing for sure the anti-seize will aid in getting a more consistent torque, say when doing a number of head bolts/nuts. Like I said I've used anti-seize and the listed torque recommendations with no problem on 60+ Yamaha 4 stroke engines. These engines were to be re-torqued at 5K per service manual, I doubt any were so I do them when I get a new one, (new to me).

[TADracer]

If you are talking about the crankcase bolts and not the cover bolts then re-use the original bolts. According to Clymers they will be of 6mm and 8mm diameters and of varying lengths. Also, they should be tightened AND loosened according to a specific sequence. Light oil is recommended to be applied to the clean threads so anti-seize should substitute for this. The 6mm bolts tighten to 8.7 lb/ft and the 8mm bolts tighten to 17.4 lb/ft. that is why I say you can re-use the original bolts because these torque values are rather low for the bolt size so bolt stretch should not be an issue.

If you are cracking the cases apart I seriously recommend a manual.

If you are talking about the motor side cover/cam cover bolts then they are all 6mm and tighten to something like 7.2 lb/ft.

All of these torque values are not much more than lightly tightened so be careful with the aluminum threads and a good inch/lb torque wrench is recommended to get evenly tightened bolts.

Hope this helps

[jetmechmarty]

to me this reduction in torque value when anti-seize is used is new to me. I always applied the listed torque and never have had any problem.
One thing for sure the anti-seize will aid in getting a more consistent torque, say when doing a number of head bolts/nuts. Like I said I've used anti-seize and the listed torque recommendations with no problem on 60+ Yamaha 4 stroke engines. These engines were to be re-torqued at 5K per service manual, I doubt any were so I do them when I get a new one, (new to me).

Yes UD, it worked, I have no doubt. Just the same, the fasteners were overtorqued. It this case the weakest link is the aluminum threads. I would expect them to strip before you snap a bolt head off. I've seen How-to's with professional mechanics recommending oil on the threads before torque. That's great if the book specifies it. My Moto Guzzi manual specifies lube torque on the page where torque values are listed and it's in bold print. In aviation, it's always clean, dry threads unless specified. I believe the same is assumed for everything else. 25% is a lot. Not something you would leave to chance.

[Artefact]

I believe the torque spec has more to do with the threads in the case than the bolts. Does that help? 8.8 might even be overkill.

Ok but it's the metric standard 8.8 = grade 5, 10.8 = grade 8 and 12.8 =even better.

[Artefact]

If you are talking about the crankcase bolts and not the cover bolts then re-use the original bolts. According to Clymers they will be of 6mm and 8mm diameters and of varying lengths. Also, they should be tightened AND loosened according to a specific sequence. Light oil is recommended to be applied to the clean threads so anti-seize should substitute for this. The 6mm bolts tighten to 8.7 lb/ft and the 8mm bolts tighten to 17.4 lb/ft. that is why I say you can re-use the original bolts because these torque values are rather low for the bolt size so bolt stretch should not be an issue.

If you are cracking the cases apart I seriously recommend a manual.

If you are talking about the motor side cover/cam cover bolts then they are all 6mm and tighten to something like 7.2 lb/ft.

All of these torque values are not much more than lightly tightened so be careful with the aluminum threads and a good inch/lb torque wrench is recommended to get evenly tightened bolts.

Hope this helps

Yes, it's the crankcase bolts. The bike was sitting for 13 years and one of the bolts snapped (they have white powder on them). I dont want to take the chance to reuse old bolts that might fail again. I will also be using zinc plated bolts (I heard that the stainless steel ones can have serious galvanic corrosion). Since I have easy access to high quality bolts, I think I'll go with 10.8 metric grade.

[jetmechmarty]

The white powder is the aluminum turning into salts.

[Artefact]

The white powder is the aluminum turning into salts.

Did'nt know that. They is also plain old rust on them.

[jetmechmarty]

Did'nt know that. They is also plain old rust on them.

The plain old rust is the steel turning into salts. It's probably on or near the head of the bolt. The zinc plating is for sacrificial corrosion. The zinc will go away before the steel. The zinc is anodic to the steel. Electrons flow from the anode to the cathode in the presence of electrolyte.