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So my exhaust valve broke. Luckily the cylinder core seems to be unaffected. My question what could have caused the valve to break apart? and if i rebuild the the head with new valves and valve guides, will this solve my problem?

I should also mention that the spark plug was not seating correctly due to a shitty helicoil job. Could a loss of compression from the spark plug hole cause the bike to run real hot?

Do you know if the valve was original? There where some popular aftermarket 2 piece valves that were prone to failure where the stem joined the head.

What's the year/model.

If there is no visible damage to the bore or head, just replace the valve and if necessary the guide too, and go riding.

ME 109 wrote:If there is no visible damage to the bore or head, just replace the valve and if necessary the guide too, and go riding.

Well. If you found all of the pieces.

enigmaT120 wrote:Well. If you found all of the pieces.

It would be amazing to not have any damage other than the valve, but I think the valve would not disintegrate any further than two pieces. As in my experience.

ME 109 wrote:

enigmaT120 wrote:Well. If you found all of the pieces.

It would be amazing to not have any damage other than the valve, but I think the valve would not disintegrate any further than two pieces. As in my experience.

+1. More details on how the valve broke. Pictures? What do the heads look like? You say No cylinder damage, what about the piston crown? The bad helicoil probably had nothing to do with the valve breaking if the valve seat was undamaged. Wrong timing, lean mixture and overheating can burn valves or cause the seat to drop out (which will break one) but valve breakage usually has something to do with parts interfering with each other or flaws in the valve (Black Diamond).

Exhaust valves on bmws do break, usually at the weld. Often no reason, I would just replace exhaust valves older than 80K miles, and even then you might not be lucky.

Charles

One of the (now) classic causes for valve failure is the dreaded valve seat recession. If its allowed to go beyond a certian point, the valve will distort and stick. It would be a good idea to seriously examine the valve seat... and also check the other side.

Rob