Cylinder Head Ache

[BMWkidd]

I experienced tankslap just outside of Prudhoe Bay last June. The left side of the bike got dinned up pretty badly.
After 2,400 miles, I still made it home. Although the idle was a bit rough and the engine noise was louder than before.
I though a little TLC will take care of that.

I finally got to do it a years later.
When I checked the valve clearances yesterday, I found out that the right cylinder was still spot on(in. 0.15mm and ex. 0.30mm),
yet the left cylinder's intake were 0.001" over and the exhaust were 0.001" under.


Then, I got to the air intake. It was greasy, (I found oil in the airbox) so I took them apart and cleaned them.


I looked into the head and HOLY SHXT! There is a crack there. No doubt, I need to replace the head, but I want to know:
1) Is the crack a result of the crash?
2) Other than a new head, what else should I get?
(item 8 ) valve guides?
(item 11) gasket?

Please HELP!!!

[riceburner]

Firstly, strip the head off fully and ensure that really IS a crack that goes all the way through.

as for the rest, not totally sure what parts will be interchangable, I know that on bike with camshafts built into the head you need to get the head and the camshaft clamps together because they're machined in the same process.

[chinist]

I'm hoping to find out what the outcome of his cracked head post was as I have the same problem. I sent him a pm....and if someone has his email, maybe they could ask him to check his messages for me. Thanks.

[boxermania]

BMWkidd

Sorry about the way that things have turned out for you. This is right up my alley and will share my read.

The crack is in a highly stressed area, let me explain. The heads are aluminum alloy and the valve seats are steel or a steel alloy. Aluminum expands more than steel and the seats are installed in the head with a fair amount of interference, so as to not come loose during the heating/cooling cycles.

There is a possibility that as the bike came down on the plastic protector and the valve cover the head could have been exposed to a force whose magnitude and direction affected the stressed area between the valves precipitating the crack. I've never seen that before, most of the time those cracks are a result of excessive heat.......

The valve lash diference between the right and left cylinder is not significant enough to add anything to the above scenario.

So what do you do?........I had a Saab Turbo that the head cracked between the seats, pretty much like yours and I had it fixed by welding. You do need to find someone that knows how to weld aluminum alloy and it can be welded up like new. That is one of the beautiful things of aluminum that cast iron doesn't have. However, bear in mind that the head has to be pre-heated to about 400 F prior to the welding and allowed to air cool.

In your case and for your piece of mind an outright replacement would be in order. Take the old head sandblast and paint it and use it as a center/conversation piece at home.

Good luck......

[TonyT607]

BMWkidd

Sorry about the way that things have turned out for you. This is right up my alley and will share my read.

The crack is in a highly stressed area, let me explain. The heads are aluminum alloy and the valve seats are steel or a steel alloy. Aluminum expands more than steel and the seats are installed in the head with a fair amount of interference, so as to not come loose during the heating/cooling cycles.

There is a possibility that as the bike came down on the plastic protector and the valve cover the head could have been exposed to a force whose magnitude and direction affected the stressed area between the valves precipitating the crack. I've never seen that before, most of the time those cracks are a result of excessive heat.......

The valve lash diference between the right and left cylinder is not significant enough to add anything to the above scenario.

So what do you do?........I had a Saab Turbo that the head cracked between the seats, pretty much like yours and I had it fixed by welding. You do need to find someone that knows how to weld aluminum alloy and it can be welded up like new. That is one of the beautiful things of aluminum that cast iron doesn't have. However, bear in mind that the head has to be pre-heated to about 400 F prior to the welding and allowed to air cool.

In your case and for your piece of mind an outright replacement would be in order. Take the old head sandblast and paint it and use it as a center/conversation piece at home.

Good luck......

"CycleRob; white courtesy phone please........"

[maduko]

Ride It.

[ProductUser]

I just replaced the left side cam tensioner (another thread), so I had a good peak in the head while I had the TB off. In my case, there was no crack or seam as your pic shows.

ProductUser

[CycleRob]

BMWkidd,

Cracks like that don't just happen unless there was an anomaly in the casting process combined with engine overheating. It's possible the shock of the crash caused the crack, but it is unlikely. A crack in that central location likely occurred when the severely overheated cylinder head grew bigger in every direction while the cool intake fuel vapor continuously cooled the intake port bridge between the valves, preventing the small area cross section from expanding as much. The opposing forces are tremendous, the expansion and contraction is very small. The aluminum is only as strong as it's weakest point.
Tink! You have a cracked intake port bridge.

You can continue to ride it. You have been already riding it for who knows how long. If you do, there's a chance a piece will break off and be eaten by the left cylinder.

For replacement parts besides the cylinder head, you'll need 4 valve seals (7) one head gasket (11) and that's all. The new head comes with 4 new valve guides (eight) already installed and figured into the price of the head. Then it's a matter of cleaning off the intake valves and swapping all the other parts to the new head. Use molly grease on the valve stems and a one inch circle of plastic draped over the valve stem's end to protect the seal from the sharp keeper valley edge. Just the left head will need to be re-torqued 600 miles later.

I considered getting the plastic crash protectors, but they decrease cooling effectiveness and only lessen the damage, not prevent it. They also add their own replacement cost to a list of parts that should not exist if they were properly designed. At best, they allow you to ride your crashed bike home while a bike w/o the guards will break it's valve cover and not be able to run without hemorrhaging oil.