bent valve rear head
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Joined: Sep 2011
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From: Canada
bent valve rear head
Hi my buddy just got his bike out of the shop it bent a intake valve on the rear head. It is a big bore shovelhead 3 5/8 bore this is the second time in the shop for that bent that valve. He didn't get 8 miles on it and it happened again. The shop told him that he is over revving it and on warranty!! so this is the third time, we pulled the head and the same valve bent, call the shop again they said he must have over revved it. I was there going down the road with my new ultima at 45 mph NO way he over revved it. fourth gear could not be more then 2500 rpm when it started to miss and pulled over and died. the A#@ hole at the shop is no help so now it is up to us to find out what is going on. I have worked on evos but not shovels. Any idea of what I should be looking for? got a new valve coming in and I am going to see what the clearance is between the piston and valve with clay. It ran before the first time for 8000 miles second time about 1000 miles last time 8 miles so something is holding the valve open. could it be the rocked? looks like a rubbing on the top of the valve spring keeper and rocker shaft. I will post pic soon. thank for any info.
Tourer
Joined: Aug 2008
Posts: 265
Likes: 10
From: Northern Wisconsin
mysterious bent valve
I know this is pretty old, but this might be helpful to other people searching for causes of bent valves. IMO, what is most likely happening here is that the valve seat is loose in the head, and once the head warms up, the valve opens, the seat drops out with the valve, gets jammed going partway back in, leaves slack in the valvetrain, the hydraulic lifter pumps all the way up to take the slack, and the next time the intake valve opens, it opens a lot further than it should, which slams the rocker into the upper spring retainer, and drives the valve into the piston. When you take it apart, it all looks perfect except for the bent valve. Remove the head and valves, heat it up to 500F, and smack it chamber down on a big chunk of wood, and the valve seat will probably go bouncing across the shop floor.
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Joined: Sep 2011
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From: Canada
I know this is pretty old, but this might be helpful to other people searching for causes of bent valves. IMO, what is most likely happening here is that the valve seat is loose in the head, and once the head warms up, the valve opens, the seat drops out with the valve, gets jammed going partway back in, leaves slack in the valvetrain, the hydraulic lifter pumps all the way up to take the slack, and the next time the intake valve opens, it opens a lot further than it should, which slams the rocker into the upper spring retainer, and drives the valve into the piston. When you take it apart, it all looks perfect except for the bent valve. Remove the head and valves, heat it up to 500F, and smack it chamber down on a big chunk of wood, and the valve seat will probably go bouncing across the shop floor.
Tourer
Joined: Aug 2008
Posts: 265
Likes: 10
From: Northern Wisconsin
valve seat repair
it depends on how big the hole in the head is. Valve seats are available in oversize sizes, so you'd have to measure it with a micrometer. I'd have to look in my notes, but I think they need .005-.007" interference fit.
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Joined: Mar 2009
Posts: 66,122
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From: Niles Canyon Ca.
Sounds like a back yard build for the motor and the clearances on deck height and valve / piston relief where not checked and setup correctly for a too big lift cam and I'd say the valve job was a fast and dirty too with the stem heights not being checked also . Only way your going to bend one is hitting the piston and if one is doing it the rest are a hair away . I'd bet the rocker arms are probably hitting on the inside of the rocker boxes too . If you have rubbing on the top collar the rocker arms weren't clearenced for the lift on the cam , shovel valve spring's are fatter than evo's and they will hit and bind . All this says the shop had zero clue about shovelheads and bigger motors .
What cam is being run ? Might want to consider finding a shop that has a clue because doesn't sound like that one does .
What cam is being run ? Might want to consider finding a shop that has a clue because doesn't sound like that one does .
Last edited by TwiZted Biker; May 1, 2012 at 01:18 PM.
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Joined: Sep 2011
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From: Canada
Guy at the bike shop said he has done tons of big bore kits I think he is full of ****. I can see where the piston hit the valve. I am going to measure the cam and see what lift it has. looks like the valve seat is in on an angle and not square there is a lip on one side I hope I can get the head fixed and he didn't f@@k it up. new valve is on its way, I will use silly puddy to find the valve to head clearance then go from there. **** load of work after he spent $3100.00 to get the top end done twice. cool old bike it is worth the time.
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Joined: Mar 2009
Posts: 66,122
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From: Niles Canyon Ca.
Guy at the bike shop said he has done tons of big bore kits I think he is full of ****. I can see where the piston hit the valve. I am going to measure the cam and see what lift it has. looks like the valve seat is in on an angle and not square there is a lip on one side I hope I can get the head fixed and he didn't f@@k it up. new valve is on its way, I will use silly puddy to find the valve to head clearance then go from there. **** load of work after he spent $3100.00 to get the top end done twice. cool old bike it is worth the time.Attachment 247932
Sounds like you have more than a clue here , if you can snap a pic of that valve and how it's seated I'd like to see that .
