1980 xs400 special spark plug cross thread

[Ronald Julian]

Hey guys need your advice please.

Had a cross threaded spark plug hole. Got a screw chaser and rethreaded it, but the weird thing is that when I tried to but in the true sort it wouldn't fit in the opening (the opening wasn't bug enough) but just beyond the opening you can tell that the rethread happened because the spark plug on its own won't fit.

So should I get a 16mm to open the lip or will I need to just take the cylinder head off and fix it that way?

Any advice would be super grateful.

Thanks in advance

 

[amc49]

That's sounds like you have cross-threaded on top of a cross-thread and death, you may as well yank head. Any 'lip' there should have cut out to allow plug to go in, it not doing so means you started way off straight with the rethread. Your idea of another thread on top is even worse, guaranteed destruction.

 

[Ronald Julian]

Gotcha bummer. So you're saying I should just buy a new head?
My question then is...I saw head's on ebay for relatively affordable prices

My questions are;
1. Should I put a new head on or can this one be saved?
2. In buying a new one (ebay their like $60) do I need to buy anything else with it (i.e. valve cover,etc) as to not compromise the overall performance of the bike
3. Is there something that in your opinion would make this switch to a new cylinder head impossible to do on my own mechanically speaking?

Thanks again

 

[xschris]

You need to get one with a numbers matched cover. They are line bored from the factory as a set. On any used sets expect to at least replace the valve seals and do a valve lap. Checking valve guides and valve stems might also be a good idea.

 

[amc49]

X2 on the matched cover. And if using your old valves on a new head they may well not lap in as every head on earth seats valves in a different way and place, sometimes it works and sometimes it doesn't. Valves already run in to matched to that head are better.So, now head w/valves and cover needed. All matched and running together previously. By far the best.

I for one do not know if the valves themselves on these can be ground, some can and some can't and the (non-OEM, never trust a Haynes to be right there) manual here onsite is not clear about it. Some valves are hard steel and can be cut and some bikes use soft steel with case hardening only on the surface and if you even lap them too much they will wear through the hardening and then the valve dies in only a very few miles with today's unleaded/ethanol fuels. Xschris would likely know the answer to that.

The original head may well be repairable but by somebody like machinist, helicoils work but are crap there, timesert is better but the install particulars often mean incompetence messes them up worse.

Can you yourself do it? No way for us to answer that at all other than if the plug threads were good before they got stripped and you were the guy that did it it screams no, you do not have the skills. You can always prove us wrong of course.

If you disassemble head to repair it all parts must be marked to go back in exactly where they were before.