MGB & GT Forum
Broken Pushrod
Posted by ssmith579
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Jul 29, 2015 10:15 AM
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My car has been running great until last night. A few blocks from home it started missing. Checked all the usual suspects like plugs and wires. Pulled the valve cover and found the following.
Jul 29, 2015 10:19 AM
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That's the second one like that I have seen in the last couple of months. Do you know the history on those push rods? Are they the cast originals, or the uprated tube style offered by some of the sellers here?
The other one failed at the casting mark. How about yours?
Have fun
If ignorance is bliss, I must be the happiest man alive!
Signed
RUFUS
67 Roadster
The other one failed at the casting mark. How about yours?
Have fun
If ignorance is bliss, I must be the happiest man alive!
Signed
RUFUS
67 Roadster
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Topic Creator (OP)
Jul 29, 2015 10:26 AM
Joined 9 years ago
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Jul 29, 2015 10:37 AM
Joined 18 years ago
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That is unfortunate. Do you think you found all the bits that came off it?
Aside from fixing it, a complete oil change is in order, and other more experienced folks will tell you what to do to avoid the missing bits from moving around the motor and going any further harm.
1974-1/2 Roadster, "Bumble Bee", Corvette Yellow - in shambles, wire wheels
1976 Roadster, "Virus", Sandglow - "driver" condition (stock + 32/36 Weber DGEV, cast iron header, 25D distributor), bolt on wheels, ON the road!
Aside from fixing it, a complete oil change is in order, and other more experienced folks will tell you what to do to avoid the missing bits from moving around the motor and going any further harm.
1974-1/2 Roadster, "Bumble Bee", Corvette Yellow - in shambles, wire wheels
1976 Roadster, "Virus", Sandglow - "driver" condition (stock + 32/36 Weber DGEV, cast iron header, 25D distributor), bolt on wheels, ON the road!
Jul 29, 2015 10:42 AM
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Aridgerunner
Bill Bussler
Montoursville, PA, USA
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Jul 29, 2015 10:45 AM
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Jul 29, 2015 11:18 AM
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Topic Creator (OP)
Jul 29, 2015 11:38 AM
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The whole engine was rebuilt. Head surfaced, block surfaced, bored 40 over, D9 CAM, 10:1 compression, all new bearings, new valves, tappets, pushrods. Oil pressure is running 50+ at idle and 70+ cruising.
In reply to # 3049227 by Motion
Was anything done to the head as well 2000 miles ago?
dickmoritz
Dick Moritz
Philly 'burbs, PA, USA
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Jul 29, 2015 11:58 AM
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Intake or exhaust?
Did you re-use original push rods and rocker arm assembly?
Did you measure exhaust valve-to-block clearance for possible interference? Did you have 0.070 minimum?
Did you enlarge the eyebrow in the block for additional exhaust valve-to-block clearance?
Dick
Errabundi Saepe, Semper Certi
(Often wrong, but always certain)
Did you re-use original push rods and rocker arm assembly?
Did you measure exhaust valve-to-block clearance for possible interference? Did you have 0.070 minimum?
Did you enlarge the eyebrow in the block for additional exhaust valve-to-block clearance?
Dick
Errabundi Saepe, Semper Certi
(Often wrong, but always certain)
Topic Creator (OP)
Jul 29, 2015 12:19 PM
Joined 9 years ago
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Going from memory, the second valve in is exhaust. Don't shoot me if I'm wrong
New pushrods (from Moss? 460-615, purchased from a vendor here), Not new rocker arm assembly.
Valve to block clearance measured, did have min but don't have the exact numbers handy.
Did enlarge eyebrows.
Using a D9 CAM but have single valve springs. I realize that I could get valve float at high RPMs but could that cause the rocker arm to come off the pushrod?
New pushrods (from Moss? 460-615, purchased from a vendor here), Not new rocker arm assembly.
Valve to block clearance measured, did have min but don't have the exact numbers handy.
Did enlarge eyebrows.
Using a D9 CAM but have single valve springs. I realize that I could get valve float at high RPMs but could that cause the rocker arm to come off the pushrod?
In reply to # 3049256 by dickmoritz
Intake or exhaust?
Did you re-use original push rods and rocker arm assembly?
Did you measure exhaust valve-to-block clearance for possible interference? Did you have 0.070 minimum?
Did you enlarge the eyebrow in the block for additional exhaust valve-to-block clearance?
Dick
Did you re-use original push rods and rocker arm assembly?
Did you measure exhaust valve-to-block clearance for possible interference? Did you have 0.070 minimum?
Did you enlarge the eyebrow in the block for additional exhaust valve-to-block clearance?
Dick
Jul 29, 2015 12:23 PM
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Joined 24 years ago
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Not it! I think that the ones I sell are made here in Oregon. That's the first broken one I've ever seen regardless of the source.
2000 miles on the engine would suggest that things were done initially in a correct manner.
Edited 1 time(s). Last edit at 2015-07-29 12:23 PM by chris.
2000 miles on the engine would suggest that things were done initially in a correct manner.
Edited 1 time(s). Last edit at 2015-07-29 12:23 PM by chris.
dickmoritz
Dick Moritz
Philly 'burbs, PA, USA
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Jul 29, 2015 12:29 PM
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In reply to # 3049272 by ssmith579
Going from memory, the second valve in is exhaust. Don't shoot me if I'm wrong
I won't shoot you, but valve arrangement is E-I-I-E-E-I-I-E ( not to be confused with E-I-E-I-O... )
Just picture the intake and exhaust manifolds. Exhaust manifolds have runners at front and back of head, and at the center where the exhaust port is shared by cylinders 2 and 3. So this is where the exhaust valves would be. Intake manifold is in between the exhaust manifold runners, and between cylinders 1 and 2 and between cylinders 3 and 4. So this is where the intake valves would be located...
Was it an exhaust valve push rod that broke? If so, suspect interference with the block. For safety's sake, I always shoot for a minimum of 0.070 clearance between the exhaust valves and the block (when building race engines we sometimes gamble on less...). If one or more exhaust valve seats were replaced, bear in mind that doing so moves the exhaust valve down closer to the block. So you can't be sure of clearances just by checking one exhaust valve; best to check them all...
Dick
Errabundi Saepe, Semper Certi
(Often wrong, but always certain)
Edited 1 time(s). Last edit at 2015-07-29 12:31 PM by dickmoritz.
Topic Creator (OP)
Jul 29, 2015 12:41 PM
Joined 9 years ago
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OK, it was an intake pushrod that broke. If you look at the first picture in the Pot #1 you can see the rocker off the side of the pushrod and valve. Guess we can rule out block interference then. I'll inspect the rod under a microscope and see if there's any evidence of a fault in the material. I'll check the valve to make sure it's not binding.
dickmoritz
Dick Moritz
Philly 'burbs, PA, USA
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Jul 29, 2015 12:44 PM
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Bronze valve guides? Minimum 0.003 stem-to-guide clearance?
Dick
Errabundi Saepe, Semper Certi
(Often wrong, but always certain)
Dick
In reply to # 3049291 by ssmith579
OK, it was an intake pushrod that broke. If you look at the first picture in the Pot #1 you can see the rocker off the side of the pushrod and valve. Guess we can rule out block interference then. I'll inspect the rod under a microscope and see if there's any evidence of a fault in the material. I'll check the valve to make sure it's not binding.
Errabundi Saepe, Semper Certi
(Often wrong, but always certain)
dickmoritz
Dick Moritz
Philly 'burbs, PA, USA
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Jul 29, 2015 12:47 PM
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Fatter hi-po push rods? Any witness marks showing that the push rod(s) might have rubbed up against the push rod hole in the cylinder head? That can happen with fatter performance push rods and high lift cams...
Dick
Errabundi Saepe, Semper Certi
(Often wrong, but always certain)
Dick
Errabundi Saepe, Semper Certi
(Often wrong, but always certain)
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