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Hi all, got a bit of an odd one.. I've been rebuilding my KZ400 engine, it was a non-runner when I bought it and after getting it all stripped down found loads of oil sludge in the crankcases, so I've been cleaning everything up for reassembly.

I had a local machine shop remove the screw in plugs from the crankshaft to be sure that all the oilways within were clear of any sludge. These plugs



All cleared out no problem, I bought new plugs to go in. The issue was that the threads appeared a little damaged from when the plugs were removed so the crank went back to the machine shop and they tapped them.

The plugs thread in fine, but they can screw further down into the hole than before, I would have thought the plugs should be tight but still flush with the top of the hole so that they can be staked?

Has anyone else had these out before and can confirm? Trying to work out what my best option is, I don't want them to work their way out once the engine is running!

Being flush at the top is much less important than them going in too deep and causing an obstruction in the oilway. Does the new thread stop short of the bottom of the hole? As long as the screw doesn't protrude down into the oil passage you can screw in tight and deform with a sharp punch to hold them in place

I'll have to double check, I'm pretty sure it did stop short of blocking off the oil passage but it was threading in so far I wound it back out till it was flush and staked it. Then thought about it a bit more and figured that might not be an ideal solution. 

The plugs will need to come back out anyway I expect. My other thought was if it's quite far down in the threads, it'll be tricky to get the punch in to stake it properly 

If the plug isn't screwed in tight you may lose oil pressure at the crank bearings ?

Yeah that was my worry as well..

Well I got one of the plugs back out and screwed it in until it went tight, can see how far it sits down the threads now. It's not showing anything blocking off the actual oilway though so I don't think it would be having any effect on oil flow to the bearings
 

adam73bgt wrote:

Yeah that was my worry as well..

Well I got one of the plugs back out and screwed it in until it went tight, can see how far it sits down the threads now. It's not showing anything blocking off the actual oilway though so I don't think it would be having any effect on oil flow to the bearings

 

Please please please, click "insert all" when posting photos.  That way the photos show up in real size, not tiny thumbnails.

Oop apologies! Let's try a different way instead

Just to be clear (your picture showed the passage is clear at the journal) if you look at the below where the blue arrow is, the black line is the oil passage through the crank which you need to be careful you don't restrict with the plug being in too deep