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Message started by Big John on 05/16/19 at 16:14:05

Title: cylinder head failure
Post by Big John on 05/16/19 at 16:14:05

Hi all My 03 has dropped an exhaust valve seat. In other words, the pressed-in valve seat has come loose from the body of the head, holding the valve open. Obviously, it won't run this way! My question of you is: have you seen this before? I can find nothing related on the forums. I would also like the opinion of some of you experienced guys on what would be the best way to fix it. I am leaning toward a replacement head. It looks like it would be very difficult to repair with any degree of reliability. What say you? :-/

Title: Re: cylinder head failure
Post by justin_o_guy2 on 05/16/19 at 16:51:40

A machine shop would be where I would be asking. They would know if it's toast.
How's your piston?
Never heard of a seat dropping out.

Title: Re: cylinder head failure
Post by DragBikeMike on 05/16/19 at 20:38:25

The bore in the head that accepts the seat is most certainly worn as a result of the seat dropping and being hammered by the valve opening and closing. It was installed with a heavy interference fit. The fit for the adjacent seat has most likely been affected and a good repair should include removing the adjacent seat and replacing it too.

I don’t think Suzuki makes oversized seats. You won’t be able to correctly repair the head unless the bores are cleaned up and oversized seats are installed. That means you will have to find suitable oversize seats. Then the seats have to be cut with the correct angles. The guides must be in good shape to do that. Of course you want to install new valves on those pristine seats. It just goes on & on.

I would replace the head with a good used head assembly (head & head cover).

Of more concern is the likely contact between valve and piston. With the valve hung open it seems likely that the piston kissed that sucker more than a time or two.

Have you checked the exhaust valve to see if it is bent? Are there telltale marks on the piston indicating contact. If the piston clobbered the valve there’s a good chance the guide boss is cracked. If it really clobbered the valve there’s a chance the rod is bent, head studs stretched, etc.

Can you post some pictures of the failure?

Title: Re: cylinder head failure
Post by DragBikeMike on 05/17/19 at 07:19:41

I forgot to add that the seat bores in the head are under significant hoop stress as a result of the interference fit. Dropped seats can be the result of cracks that develop in the aluminum. The crack relieves the hoop stress and then there’s no interference between the seat and head. To help us all understand your failure better, can you give a good look to the head around the seat bore and tell us if you see any cracks emanating from the seat bore. 5X magnification would be helpful for your inspection.

Title: Re: cylinder head failure
Post by Big John on 05/17/19 at 07:42:35

Will post some pics next week. Thanks for the responses. I have ordered a used head from e-bay.

Title: Re: cylinder head failure
Post by LANCER on 05/17/19 at 10:35:07

A really good magnifier is helpful.

A head I rebuilt a couple years ago an a high milage engine needed all the valves replaced, but could not be seen with the eye. I used a 10x mag. with a 2x mag. to be able to see numerous cracks around the outer edge of each valve.

Title: Re: cylinder head failure
Post by Armen on 05/17/19 at 20:44:59

IIRC there was a short run of BMW 250 singles in the 60's that were known to do that. My '79 XL250 dropped an ex seat.
With the BMWs, the parts were scarce and expensive, so I sent them out to be fixed. Machine out the seat boss, TIG weld up, re-machine, install seat. Use the guide bore as a locating device. Unless the guide was toast, Then...
Needless to say, unless you have a machinist that works for free, or have the equipment yourself, a good used head makes sense.
On my XL, I bought a new head.

Title: Re: cylinder head failure
Post by DieselBob on 05/18/19 at 04:00:02

-
Remember, there's always that guy in Hungary that does Savage heads.

http://https://img.index.hu/imgfrm/1/2/5/0/MED_0014181250.jpg

Title: Re: cylinder head failure
Post by Big John on 05/23/19 at 20:56:36

Here is the top of the piston.

Title: Re: cylinder head failure
Post by batman on 05/23/19 at 22:34:41

I'm no expert ,but the piston looks useable to me , but if you found it that way , (you haven't cleaned it ) it would go along way toward explaining your valve failure, the piston should show a carbon coating,(that acts to protect it from the heat of combustion) the fact that it doesn't , means the motor was running very lean (hot) and the exhaust valves sees the most of that when open, so would likely be the first to fail.

Title: Re: cylinder head failure
Post by DragBikeMike on 05/24/19 at 14:38:16

It certainly looks like some small foreign objects were rattling around in there. All those little divots look ugly. I see one eyebrow that looks like a pretty good kiss with a valve. Was it your left hand valve seat that dropped? Do you have any idea what caused all the little divots? Do you have any pictures of the combustion chamber? Some close-ups of the failed seat and the combustion chamber?

Title: Re: cylinder head failure
Post by Big John on 06/22/19 at 10:00:01

Would like to post pics, but site says 978KB pic is too large. Will keep after it.