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I've rebuilt a 66' 450 and I guess I'm looking for another opinion before I yank it out again. New pistons, valves,..it was running great..no smoke/leaks. After about 50 miles of running the right side started burning white/blue smoke and I mean alot! I took it home, grabbed a beer and let it cool down. (feeling very depressed/angry haha..) I took the plug out and I could see oil in the cylinder. Any Ideas? I'm thinking a valve guide but just throwing it out there.
 

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I would be surprised if it was a valve guide since they don't just "fail" like that. In the same way, I've never seen a piston ring break during regular use but it's possible. More likely than not, my money is that the head gasket blew as Znabb mentions.
 

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The exact same thing just happened to me. Did you put larger pistons in?
 

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That compression test would tell for sure if the gasket blew...
 

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Mine just started leaking on Sunday. I have to remember to bring my compression tester home from work. I'm pretty bummed about it too, I don't really want to tear it apart again.
 

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Hi,

The reason of blowing gaskets, just after a rebuild, could be due to not re-torquing the head.
After assembly of the head the bolts should be put to the specified torque. After the first cycle (a short ride, cold, warm, cold) the head should be re-torqued.

It seems to be a lot of work (it is !), but it is absolutely necessary.
I re-torque the head twice, once as described above, and again after 200 - 500 miles or so (after the first long highway ride).

I've never experienced a blown head gasket (with CB72 / 77 's) but I don't know if this is due to the method I describe.

(I assemble the head nuts with a mixture of copper grease, graphite and a few drops of oil, and before re torque I lose the nut a little bit (no more then 1/8 turn), and then set to the specified torque, this is done in the same sequence as described in the manuals, thus from the inner to the outer nuts)

Jensen
 

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Jensen, as not all of the 450's head nuts are accessible in the frame without removing or at least unbolting and tilting the engine. Do you unbolt the engine twice and retorque the head after a rebuild?

I would like to hear the experts view on torquing the head nuts wet (with oil, grease) like Jensen suggests. I've learnt that torquing nuts/bolts wet or dry is two different things and mostly the torque recommendations in manuals are dry torque.
 

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My understanding is that, unless specifically stated otherwise, torque specifications are for DRY assembly. Lubricated assembly will lead to substantially higher bolt tension than dry assembly at the same torque. The difference, of course, will depend on the lubricant but from what I have read you could have bolt tensions close to twice as high for lubed compared to dry!

Mike V.
 

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Hi,

Indeed, forgot to mention, the specified torque is indeed always specified as dry. The difference between dry and lubricated torque is between 10 to 20 % for M8, no more. Stay on the save side and lower the specified torque with 20 %.

Jensen
 
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