Broken Exhaust Valve Guide SBC
06-20-2010, 08:46 PM
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Broken Exhaust Valve Guide SBC
Hello,
This is my first post, usually I can find my answer from everyone else's information but I am stuck on this one.
I have a 1986 260 Mercruiser (SBC), rebuilt 4 years ago. The stock heads were rebuilt and a Comp Cams XM 256 cam installed with Comp Cams 918 springs and Magnum Roller Tip Rocker arms. I used Magnum pushrods that were 0.050" shorter then stock which I though gave the best geometry.
This week I discovered I had a broken valve guide on #1 exhaust after trouble shooting an erratic miss at idle and a ticking from the rocker arms. After pulling a couple other valves I noticed the other guides look pretty good.
The guides were installed 5 years ago and I have put about 350 hours on the engine since the work was completed.
Any thoughts on the cause? Poorly installed guides? Wrong length pushrods? Just old age?
I find it odd it ran for so long, but I am not sure when it starting actually cracking.
Thanks for your help... maybe I can start to contribute these forums more in the future!
This is my first post, usually I can find my answer from everyone else's information but I am stuck on this one.
I have a 1986 260 Mercruiser (SBC), rebuilt 4 years ago. The stock heads were rebuilt and a Comp Cams XM 256 cam installed with Comp Cams 918 springs and Magnum Roller Tip Rocker arms. I used Magnum pushrods that were 0.050" shorter then stock which I though gave the best geometry.
This week I discovered I had a broken valve guide on #1 exhaust after trouble shooting an erratic miss at idle and a ticking from the rocker arms. After pulling a couple other valves I noticed the other guides look pretty good.
The guides were installed 5 years ago and I have put about 350 hours on the engine since the work was completed.
Any thoughts on the cause? Poorly installed guides? Wrong length pushrods? Just old age?
I find it odd it ran for so long, but I am not sure when it starting actually cracking.
Thanks for your help... maybe I can start to contribute these forums more in the future!
06-20-2010, 08:58 PM
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Fixx
Hello,
This is my first post, usually I can find my answer from everyone else's information but I am stuck on this one.
I have a 1986 260 Mercruiser (SBC), rebuilt 4 years ago. The stock heads were rebuilt and a Comp Cams XM 256 cam installed with Comp Cams 918 springs and Magnum Roller Tip Rocker arms. I used Magnum pushrods that were 0.050" shorter then stock which I though gave the best geometry.
This week I discovered I had a broken valve guide on #1 exhaust after trouble shooting an erratic miss at idle and a ticking from the rocker arms. After pulling a couple other valves I noticed the other guides look pretty good.
The guides were installed 5 years ago and I have put about 350 hours on the engine since the work was completed.
Any thoughts on the cause? Poorly installed guides? Wrong length pushrods? Just old age?
I find it odd it ran for so long, but I am not sure when it starting actually cracking.
Thanks for your help... maybe I can start to contribute these forums more in the future!
This is my first post, usually I can find my answer from everyone else's information but I am stuck on this one.
I have a 1986 260 Mercruiser (SBC), rebuilt 4 years ago. The stock heads were rebuilt and a Comp Cams XM 256 cam installed with Comp Cams 918 springs and Magnum Roller Tip Rocker arms. I used Magnum pushrods that were 0.050" shorter then stock which I though gave the best geometry.
This week I discovered I had a broken valve guide on #1 exhaust after trouble shooting an erratic miss at idle and a ticking from the rocker arms. After pulling a couple other valves I noticed the other guides look pretty good.
The guides were installed 5 years ago and I have put about 350 hours on the engine since the work was completed.
Any thoughts on the cause? Poorly installed guides? Wrong length pushrods? Just old age?
I find it odd it ran for so long, but I am not sure when it starting actually cracking.
Thanks for your help... maybe I can start to contribute these forums more in the future!
i would find a set of vortech heads and a intake to match,,their worth the xtra 40 hp
06-21-2010, 10:05 PM
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Thanks for the input.
I am using 1.5 ratio rocker arms, the valves look pretty good so I don't think it detonated. The machine shop noted the exhaust valve seats were pretty wide indicating some wear though.
I decided to purchase a new set of assembled World heads and just chalk this up to being worn out. I think I will stick with the self aligning Magnum rockers and do my best to check pushrod length.
Because of the pistons I have I need to stick with 76cc heads to keep the compression ratio down but I went up from 1.94" to 2.02" because they are available sooner. Our season is too short for summer breakdowns!
Thanks again!
I am using 1.5 ratio rocker arms, the valves look pretty good so I don't think it detonated. The machine shop noted the exhaust valve seats were pretty wide indicating some wear though.
I decided to purchase a new set of assembled World heads and just chalk this up to being worn out. I think I will stick with the self aligning Magnum rockers and do my best to check pushrod length.
Because of the pistons I have I need to stick with 76cc heads to keep the compression ratio down but I went up from 1.94" to 2.02" because they are available sooner. Our season is too short for summer breakdowns!
Thanks again!
