Head gasket question

Mailman · Nov 16, 2018

On someone else’s thread we were talking about different gasket kits and Grizld1 stated that Athena head gaskets being thicker than OEM would cause the timing to be advanced.
I wish to understand this. Could someone please explain the cause and effect of a too thick head gasket on timing please.
Thanks.

650Skull · Nov 16, 2018

Post #1 explains this in detail............Using the Athena head gasket, being slightly thicker, i would think just by shifting the points plate to correct the advance, the head gasket causes, would be simple enough solution to get it back to normal..........In the link 2 head gaskets are used so there is a substantial difference in the head being raised compared to the Athena gasket thickness.........Also shows how much the cam sprocket has to be mover to get the advance back to factory setting.

http://www.xs650.com/threads/a-collection-of-xsjohns-mods.2426/

grizld1 · Nov 16, 2018

Valve (cam) timing, not ignition timing. As viewed from the left, lowering the deck causes the tensioner to rotate the camshaft CW, retarding valve timing. Raising the deck rotates the camshaft CCW, advancing valve timing. Of course with camshaft driven ignition, spark timing will also move, but adjustment is easy, as Skull notes.

GLJ · Nov 16, 2018

Stare at the stater side. Visualize what would happen to the cam as the head is lifted. Chain length increases so the cam has to rotate to adjust. The tensioner at the other side retracts.

Mailman · Nov 16, 2018

Thanks guys, that helps. I get it now. :thumbsup:

gggGary · Nov 16, 2018

The devil made me say it. :devil:

The cam sprocket is pressed on, cam timing is completely adjustable. :smoke:

We need 2many to do the math!

grizld1 · Nov 16, 2018

No need to pester 2M, Gary. Pythagoras did the formula back when we were kids.

TwoManyXS1Bs · Nov 17, 2018

Thanx, griz. But, already done:

Move the head by 0.388mm (about 0.015") will result in 1° (at the crank) of camshaft timing change.

Post #19.
http://www.xs650.com/threads/when-to-rebuilt-engine.46862/#post-469432

grizld1 · Nov 17, 2018

Yep, a change of only 1* is insignificant in itself. But if there's also a bit of grind error, lobe wear, etc. in the picture (and there usually is), it can add to the trouble.

gggGary · Nov 17, 2018

Didn't XSJohn reclock the cam sprockets?

grizld1 · Nov 17, 2018

Yeah he did, after I told him how to convert degrees of correction into distance to move sprocket in a PM--he never asked a question on open board or gave credit for information received. He doubled up head gaskets, raising the deck quite a lot: ~.043". John claimed the motor ran badly with the sprocket in the OE position and cam timing advanced by the extra gasket, claimed OE timing was "advanced to the wall." I found that questionable, but said nothing; got a hunch that something else was going on and that reassembly straightened it out, but who knows?

Head gasket question

Mailman

Hardly a Guru

650Skull

Cockytoo

grizld1

Grumpy old man

GLJ

Never go faster than your guardian angle can fly.

Mailman

Hardly a Guru

gggGary

If not now, When?

grizld1

Grumpy old man

TwoManyXS1Bs

BBQ Hunter

grizld1

Grumpy old man

gggGary

If not now, When?

grizld1

Grumpy old man

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