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Yamaha F4 4 stroke outboard crankcase bolt torque specs

H

hungyzerglin

New member
Put in a new piston and rings for this motor, but ran into problems with snapped crankcase bolts when torqueing to service manual specs:
f4-crankcase-bolts.PNG

I had no problems getting to the first torque value (7.2 ft-lb), but I snapped 2 bolts torqueing to the final 16 ft-lb value:
tlPf9vu.jpg

Are these bolts torque to yield or reusable (they seem like just regular stainless steel M6 bolts)? Can I leave the crankcase torqued to 7.2 ft-lbs or will I have leakage problems? I ordered new bolts just in case, but I would prefer not to snap anymore.
 
Hi hungyzerglin - What brand wrench are you using? Are you using a 1/4" drive in/lb torque wrench or a 3/8" ft/lb? I know some 3/8 drive are 10-100 or 0-75, I wouldn't trust anything on the lower end of one of those torque wrenches for something that small, they're generally only accurate in the upper 80% of the range. I would definitely torque in 3 sequences, such as 72 in/lb, 132in/lb , then 192, cross tightening then going over it again for a total of 6 sequences. I can't recommend leaving a crucial part like that at less than half the specified torque or using anything but the factory M8x50mm bolts and new gasket. Though I have reused those bolts and doubt you'd have a problem, most the newer service manuals call for new bolts on a lot of parts. I think a leak would be inevitable in that torque range, I think there's a bigger difference between 7 vs 16, especially with a gasket/oil involved, than 90 vs 99.
 
vienscomarine said:
Hi hungyzerglin - What brand wrench are you using? Are you using a 1/4" drive in/lb torque wrench or a 3/8" ft/lb? I know some 3/8 drive are 10-100 or 0-75, I wouldn't trust anything on the lower end of one of those torque wrenches for something that small, they're generally only accurate in the upper 80% of the range. I would definitely torque in 3 sequences, such as 72 in/lb, 132in/lb , then 192, cross tightening then going over it again for a total of 6 sequences. I can't recommend leaving a crucial part like that at less than half the specified torque or using anything but the factory M8x50mm bolts and new gasket. Though I have reused those bolts and doubt you'd have a problem, most the newer service manuals call for new bolts on a lot of parts. I think a leak would be inevitable in that torque range, I think there's a bigger difference between 7 vs 16, especially with a gasket/oil involved, than 90 vs 99.
Click to expand...

Vienscomarine, thanks for your input. Now that you mention it, I used a 1/4 torque wrench for the first sequence, then a 3/8 for the second sequence where the bolts broke. Once the new bolts arrive, I will try the 3 sequence torque with just the 1/4 wrench and re-tap all the bolt holes to clean them out.
 
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