Crankshaft drilling plug question

[adam73bgt]

A question for the engine gurus, I'm currently rebuilding an engine from a Kawasaki z400, it had some evidence of sludge in the sump when I stripped it down so I've had it completely apart and have been cleaning everything to within an inch of its life

The crankshaft is in good condition but to be sure it was totally clean through all the oilways I had a machine shop take out the small threaded plugs which plug up the original drilling holes



In doing so, I think they damaged the thread slightly so I took it back and they've tapped the threads, I have new plugs which screw in fine but I don't know if they've tapped further down than the original threads as the plugs will screw right down into the hole.

Before they were stripped, the plugs sat fairly proud so that the egdes could be punched so they don't wind out



So I'm not sure what's best to do, if I screw them right in till they're tight, I wouldn't be able to punch them to hold them in place. If I only screw them in far enough that I can still punch the edges will they stay in place? Last thing I want is one of them backing out while the engine is running 😅

[colnerov]

I would be more worried about the balance of the crank, considering how high bike engines rev.

[Darkspeed]

Unlikely to screw in if you left them flush - both centrifugal force and oil pressure are acting to throw/push them out - High strength Locktite and stakes should do the trick from prventing them coming out. But, they also need to be a good tight fit in the threaded hole to seal it off - Otherwise its a leak path that could reduce the available pressure at the bearing.

[ChasR]

Hi Adam,

I can put you in touch with someone who rebuilds bikes, and bike engines. He's based in Kenilworth and Coventry, if that is any good to you?

[adam73bgt]

Oct 26, 2023 16:57:05 GMT colnerov said:

I would be more worried about the balance of the crank, considering how high bike engines rev.

I hadn't considered that particularly, it should be pretty close to the original balance. It's not a particularly sporting engine and does feature some chain driven balance weights as well so I'd hope it should be forgiving of any slight differences

Oct 26, 2023 19:23:26 GMT Darkspeed said:

Unlikely to screw in if you left them flush - both centrifugal force and oil pressure are acting to throw/push them out - High strength Locktite and stakes should do the trick from prventing them coming out. But, they also need to be a good tight fit in the threaded hole to seal it off - Otherwise its a leak path that could reduce the available pressure at the bearing.

Yes them screwing out rather than going further in was my concern. To be honest I initially put them back in with some regular blue loctite and staked them before thinking about it a bit more. I guess if they're not tightened down to the end of the thread then as you say oil could try and leak up the threads..

Oct 26, 2023 19:26:38 GMT ChasR said:

Hi Adam,

I can put you in touch with someone who rebuilds bikes, and bike engines. He's based in Kenilworth and Coventry, if that is any good to you?

Yeah sure mate, sounds like could be a handy person to chat to

[adam73bgt]

OK so I screwed one of the plugs in as far as it would go, better illustrates the difference to how it was from factory



There's no sign of it impeding oil flow through to the bearings



So I'm thinking install it like that with some permanent loctite? Haven't really got the access to stake it that far down in the hole

[stealthstylz]

Will be fine like that with loctite to seal the threads.

[slater]

I'd loctite and just stake the end of the threads so if it ever did move it wouldn't come out. Belt and braces.