Leaking head gasket and testing if valves seal?

[Stabler]

I pulled the head of my XS400 4g5 1983 motor a couple of nights ago, due to a leaking head gasket. Now I didn't find any damage to the head gasket but quite a bit of grime on the fins where the leak(s) is. I tried the search field, but didn't turn up anything useful on these questions, maybe I'm doing it wrong?


- My first question is, is there enough material on the head to have it ground down (is that the correct term?) like 0,5 mm or maybe even 1 mm (or maybe even more)? Does anyone know how much there is to remove there without risking the pistons hitting the valves?


- Second, does anyone know if it's possible to test the seal between the valves and the head by spraying WD40 (or CRC 5-56) on top of the valves and see if it leaks throug in to the top of the combustion chamber? I've read something about this somewhere, but can't remeber if it was a good way to do this.. My other choice is to have the head pressure tested at a shop but that is to much $ for my taste.
Is there any other way of testing the valve sealing to the head with the head off?


- And last, what torque do I use and in what order do I tighten the head nuts and then the valve cover bolts? (Oh - and what number Yamabond is used to seal the valve cover?)


A lot of questions in one thread, I know, but rather this then clutterin' the forum with multiple threads..

Any help here is much appreciated,
Thanks.

 

[bcware]

Is your head warped? Why do you want to remove material? Are you trying to raise compression?

Test the valve's seal by laying the head on your desk upside down with the valves in (the springs and such do not need to be installed). Fill the recess with some kind of solvent. If the solvent starts draining on to your desk the valves aren't sealing well. The valves should contain the liquid even without any spring pressure holding them in place; gravity alone should do it.

The torque sequence is in the manual that can be downloaded from the sticky post in this forum.

The valve cover is machine-matched and doesn't need a sealant, but some manuals recommend it; I use a little bit myself. Any non-hardening engine sealant should work fine; use it sparingly. I have been using Threebond 1194 on pretty much everything; it's good stuff.

 

[Stabler]

Thanks bcware.
I don't know if my head is warped, but I have leaks on both sides between my head and cylinder and no sign of damage to my head gasket. So I'm thinking of taking 0,5 - 1,0 mm of just to be sure. Is there enough material there? It looks tight with the valves..

Thanks again!

 

[bcware]

The head gasket will tend to leak a bit after a few decades. If you don't have a time reference you really don't know if the oil you're seeing is from a significant leak or just a slow weep over a decade or more building up. The manual recommends checking the head and jugs with a flat edge before decking them.

A machinist would better be able to answer your question about clearance and they'll need to do the work anyway.

If you can't see any imperfections in the surfaces you might just try replacing the gasket, oil seals, and throwing a little sealant on the paper area of the head gasket.

 

[Stabler]

I forgot to mention that I also hear a sound (let's see how I best describe this in english) when accelerating. It's like a high pitch "poff" at every detonation in the engine. Just when accelerating and only off the right side of the motor. From between the head and cylinder I imagine.. And this sound wasn't there when I bought the bike last year.

Does that change anything you think?

Thanks again bcware.

 

[bcware]

If you've got everything apart I would just inspect everything for abnormal wear:

The cylinder walls for scrapes.
The piston crown for damage (valves making contact).
The valves and valve seating area for damage or pitting (debris can cause this if it gets in the engine.)
Check the valves for free lateral play (valve guides).
Inspect the cam for abnormal wear, especially at the smooth round portion that makes contact with the head and valve cover.
Check valve clearances when everything is reassembled and check the ignition timing if you have points.
Check the valve/cam chain timing and make sure the cam chain tensioner is working.
Check for exhaust leaks at the exhaust port/header area; make sure you replace the copper gaskets.

This should get you started!

 

[Stabler]

Thanks bcware. I'm on it.

 

[Scorpio1963]

If you suspect warpage on the head take and lay it on a flat level surface and look for gaps around or light or you can use something like a flat ruler and lay across the head from corner to corner.As for machining the surface .05 .10 thousands I dont beleive is going to hurt anything.I know theres a thread covering the same topic where the user was asking about milling a certain amount of surface area to raise compression.You might want to search that out for more info.Hope that helps.