Loctite on crankcase bolts

After putting about 2500 post-resto km's on my 750H I noticed a tiny bit of oil between the cases behind the pipes. I checked the M6 crankcase bolts and they were loose. I think that the paint between the case and the flange may have given just enough to allow the bolts to vibrate loose - they were torqued to spec during the rebuild.

I will go through all of them (including the M8 crank bolts) before I get back on the road in spring. I was wondering if I should put some blue Loctite on all of them.

Kawasaki says to not use loctite (except for certain bolts) so I haven't used it except where they say to use it.. I've never noticed a loose bolt on my three rebuilds.

That's what I figured as the service manual said no thread lock or liquid gasket. I thought it might have been a common problem but I guess not. I'll put it down to the paint being baked and shrinking a bit. I guess the fix is tighten them up and keep an eye on them

Make sure the holes and threads are clean and dry before re-installing bolts. Ed

Will do. I'll be taking them out one at a time, cleaning them and putting them back in. Should be pretty meditational... :huh:
I did wonder if it might be due to the flanges on the stainless bolts I used - they are a bit larger than the stock bolts so the pressure on the mating surface might not be enough... I guess I'll swap them out if it happens again.

You should also clean and chase each hole in the cases to ensure they are clean right to the bottom. It's time consuming but worth the effort. The flange on the bolt head shouldn't cause any problems. Just be sure to use a torque wrench to tighten the bolts to the correct torque. Off the top of my head, the M8 bolts are torqued to 18 ft lbs and the M6 bolts are torqued to 72 inch lbs. The manual will have the proper numbers. Do not over torque.

I wouldn't do anything other than torque the screws again. Don't remove them, just crack them loose about 1/8 turn and then tighten to spec. Target the low end of the torque range because it's really easy to strip crankcase screws, particularly the 6mm ones.

Ed: that's what I have done with the front ones. I will pull at least one or two out where the head was covered in oil. Will torque to 10Nm as I did last time (there is no range given on the crankcase bolts, just 1.0 kgm).

hardrockminer: The threads in the cases should be really clean. Everything got a thorough cleanout during the rebuild and all the bolts were replaced. Also, I never go anywhere without my torque wrench


From all of the answers here it was probably just the paint settling with the engine heat that dropped the torque off just enough for them to vibrate loose.

What are the specs on the replacement stainless steel bolts ??
I tried stainless bolts in the past and they stretched so they wouldnt hold a torque spec
Next time dont leave paint on a mating surface
Dave

They're A4-70 so [strike]about[/strike] almost as hard as 8.8 steel fasteners. You're right about the paint - I masked the surfaces for the M8 crank bolts but didn't bother with the rest. I guess the price is a slightly more regular check of all the bolts.

Golden rule is no paint on sealing surfaces. Must be metal to sealant to metal, or metal to gasket to metal. I always clean mating surfaces with scotchbrite before assembly. Don't know about loose bolts, but it's gonna leak if there's paint on the surface.

Honda cars had a TSB out a while back on valve cover gaskets leaking on the 2.4L L4. It was due to overspray on the cover's gasket surface. The fix was clean off the paint and replace the gasket.

When I read the OP, I get the impression he is referring to paint on the crankcase under the flanges of the bolts, NOT paint on the mating surfaces of the crankcase?

Mike