Blown O-ring

Message

Kuma · #1 Post by **Kuma** » Mon Apr 13, 2009 3:48 am

was riding at Glamis, shut the motor down for a break, when I tried to restart steam came out of the exhaust.
this motor has about 2/3 season at the dunes.
I need help to figure out what happened.
How to prevent it.
How to repair.

Noticed shortly after a blast up hill 5 and a quick pace twords olds.

This is a Timbo 495 motor.
The inner O-ring blown, parts of the oring missing, cylinder had plenty of coolant in the cylinder.

[attachment=8343:108_3718.JPG][attachment=8344:108_3719.JPG]

There is some damage to the head, looks like the cylinder beat in a bit of a groove in the head, all the head nuts were tight.

claas900 · #2 Post by **claas900** » Mon Apr 13, 2009 4:13 am

Whats happening is the cylinder is moving like its breathing larger then smaller wearing a grove into the head. Is there a way to stop it? Not that i know of. There is a slight chance that the sleeve is sitting to low into the case. How does the lip on the sleeve look? You'll have to resurface the head. I'm 90% sure this problem is going to be bigger with us dune guys. I may have a used 98mm +6mm piston for sale.

thedeatons · #3 Post by **thedeatons** » Mon Apr 13, 2009 4:14 am

Loose head nuts (not torqued or Loc-Tited)

Lack of RTV on the o-rings

Chipped cylinder

Is your head pock marked by the valve faces? Water based coolant will do that to the aluminum...

claas900 · #4 Post by **claas900** » Mon Apr 13, 2009 4:16 am

Funny I've never put RVT on the head O-ring. i would think it wold hurt it more then help it.

Kuma · #5 Post by **Kuma** » Mon Apr 13, 2009 4:41 am

QUOTE (thedeatons @ Apr 12 2009, 09:14 PM) <{POST_SNAPBACK}>

Loose head nuts (not torqued or Loc-Tited)

Lack of RTV on the o-rings

Chipped cylinder
Is your head pock marked by the valve faces? Water based coolant will do that to the aluminum...

Head nuts were tight though I did not check what the torque was as I was removing them.

I did have RTV on the orings, as stated above I was not sure it the RTV contributed to the failure.

Valves and piston look fine, no marks.

That is 100% Evans coolant pooled on the cylinder.

Kuma · #6 Post by **Kuma** » Mon Apr 13, 2009 4:49 am

QUOTE (claas900 @ Apr 12 2009, 09:13 PM) <{POST_SNAPBACK}>

Whats happening is the cylinder is moving like its breathing larger then smaller wearing a grove into the head. Is there a way to stop it? Not that i know of. There is a slight chance that the sleeve is sitting to low into the case. How does the lip on the sleeve look? You'll have to resurface the head. I'm 90% sure this problem is going to be bigger with us dune guys. I may have a used 98mm +6mm piston for sale.

Is the groove in the head something that you have seen?

When I take the cylinder out I'll get an accurate depth measurement of the cylinder pocket and a measurment of the cylinder, shoulder to the top. Should the measurment be the same or should the cylinder be a couple thousands taller?

I should have a good look at the piston and cylinder tomorrow, hopefully that's all good.

claas900 · #7 Post by **claas900** » Mon Apr 13, 2009 4:50 am

I'm sorry I meant to say 97mm fs. That head O-ring looks like a stocker? I just put in a 98mm this weekend and it came with a new O-ring that looked thinner then stock.

Kuma · #8 Post by **Kuma** » Mon Apr 13, 2009 4:58 am

QUOTE (claas900 @ Apr 12 2009, 09:50 PM) <{POST_SNAPBACK}>

I'm sorry I ment to say 97mm fs. That head O-ring looks like a stocker? I just put in a 98mm this weekend and it came with a new O-ring that looked thinner then stock.

The Orings are, were Viton from Boomer.
Any suggestions for cleaning the groove in the head?

Trouble · #9 Post by **Trouble** » Mon Apr 13, 2009 9:19 am

i didnt use any sealant on the oring when i did mine.try and double check the head surface for flatness after you get it cleaned up,it appears that you may have caught it in time befoe you did any real damage hopefully,i do wonder have a oring managed to come apart though.i wouldnt have the head decked unless yours is warped because that seems to cause more problems if the machinist doesnt know what they are doing,hopefully you can get away with just another o ring replacement.

claas900 · #10 Post by **claas900** » Mon Apr 13, 2009 10:14 am

QUOTE (Kuma @ Apr 12 2009, 09:58 PM) <{POST_SNAPBACK}>

The Orings are, were Viton from Boomer.
Any suggestions for cleaning the groove in the head?

I'm sure just a light resurface job would clean it up. That I know of theirs no way to fix a liner tho,I'd be looking really close at its matting surface to make sure its flat. As for O-rings I know at one time Tim didn't send one with the kits you just used a stock one, but like I said the 98mm I did this weekend did come with one and tho I didn't compare it with a stocker it sure looked thinner.