Checking Cylinder Head for Warpage

[YL82]

I've got (work) access to some high-grade granite Starrett Surface Plates to check my cylinder head for any warpage or un-flatness

Do I need to use something so accurate or is using a precision straightedge and feeler gauges at several locations generally adequate?

Or even using plate glass to check for any rocking?

Perhaps a silly question, but does the top of the cylinder block also need to be checked as well or just the cylinder head?

Thanks.

 

[jd750ace]

If you have it all apart, do both parts and use the surface plate for the optimum check-out. Gaskets will deal with some uneven surfaces, but the closer to perfect it is, the less stress the gasket will have. We used to re-surface pneumatic valves that had warped on a surface plate with wet/dry aluminum oxide paper taped down to it.
You'd be amazed how wavy some plate glass can be.
Use the best tools you have available to you when it comes to accuracy. Necessary, maybe not, but what I'd do in your situation.

 

[YL82]

Sounds good, jd750ace.

What about the cover (for valves, camshaft) ? Do I need to check that for warping too or just the cylinder block and cylinder head?

This is my first time doing any of this stuff.

Thank you.

 

[jd750ace]

I wouldn't expect the cover to be any kind of issue, but if you are inclined, why not?

 

[Uncle Bryan]

It's ok to check the cover just for giggles, if you want, but don't try to do any lapping or anything on it. The cover and head were mated at the factory and machined together as a single unit. If it doesn't checkout flat, don't sweat it, check it on the head, that's what counts. And even if that doesn't check out, I still wouldn't sweat it unless it's really off.
Bryan

 

[YL82]

A very basic follow-up question: What is the typical cause of head warpage?

Overheating?

 

[jd750ace]

Overheating of the whole assembly or one cylinder significantly hotter than the other. I'm sure that's not all.

 

[YL82]

The reason I've taken my engine apart (aside from the sheer fun of it) is I had zero compression on the left side. Turns out that I have a bent left intake valve. I was running on one cylinder.

I wonder whether there is any correlation between a bent valve and warping of the head. I suppose I'll learn more about that possibility when I use the surface plate next week...

 

[TwoManyXS1Bs]

Riding in the rain, crossing a creek or puddle, going underwater...

 

[Brian902]

Bent valves and warped heads don't usually go hand in hand.

Bent valves are normally caused by sticking valve guides, valve gets held open and then the piston kisses the valves and bends it because they hate each other.

Or, over adjusted valve clearance, too tight that is, and again the piston kisses the valve and they hate each other so it gets bent again.

Or someone put something down the plug hole while tuning and inadvertently bent the valve and didn't know it.

Over reeving and valve float, a possible other cause. Again the piston kiss of death.

I bent one when my head was off and had the assembly together doing some cam testing. One valve, not sure which one, was open and when I set the head down it caught the edge of the valve and bent it. Costly mistake.

Head warp is usually over-heating and or loose head bolts leaving you with constant oil leaks/low compression along with oily pants your wife hates to put in her clean washer.

 

[jbbishop2]

I've been wondering about this myself, since my '81 got hot and puked oil between cylinder and head. I've measured the flatness of my head with a Starrett straightedge and found a maximum of 0.0015" near the middle. I didn't know what was acceptable but found a number in the Yamaha service manual for the '82 model. A scan of that section is below (if it works; I've had bad luck getting images into my posts here). It says the head must be resurfaced if the warpage exceeds 0.0012", and the head should be replaced if it exceeds 0.010", the allowable limit.

I'm pretty close, and the stock head gasket is 0.043" thick (some aftermarket ones are 0.060". I'm still undecided about whether I should get the head resurfaced or just put it back together with new gaskets. A good local performance machine shop that understands motorcycles (Engine Dynamics in Petaluma, CA) charges $85 to resurface the head on a twin.

The warpage check in the manual is at

.

 

[gggGary]

I don't ever recall anyone having a warped head on an XS650, not saying it can't happen but it's a pretty thick casting lot's of stability there. I don't think I would sweat your .0015"
As suggested it you are obsessive some time with paper on a flat surface should help.

Brian seemed to cover it well. Specially the oily pants thing.

 

[YL82]

Just had a Machinist at my workplace check out my cylinder head cover and head on a DoAll granite Surface Plate.

Results: No warpage, so the trend continues, gggGary! Thankfully.