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Broken Pushrod

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ssmith579 Avatar
ssmith579 Steve Smith
Ventura, CA, USA   USA
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1974 MG MGB
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.


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Rufus Avatar
Rufus Gold Member Harry Singleton
Deep in the East Texas Piney Woods, TX, USA   USA
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1967 MG MGB "The White Car"
1967 MG MGB GT Special "Rusty"
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



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RUFUS
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ssmith579 Avatar
ssmith579 Steve Smith
Ventura, CA, USA   USA
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1974 MG MGB
The pushrods were new about 2000 miles ago. They are the stock type for an 18V engine.

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BumbleB74 William Milholen
Tidewater, Tidewater VA, USA   USA
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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!

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Rod H. Avatar
Amity, OR, USA   USA
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1964 MG MGB
1968 MG MGB GT
Sounds like there are some bad new pushrod out there. )-:



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Aridgerunner Bill Bussler
Montoursville, PA, USA   USA
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1956 MG MGA 1500 "The A"
1959 Triumph TR3A "The Mistress"
1977 MG MGB "Sweet B"
Can you provide us with name of the supplier and the country of origin?



?

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Motion Avatar
Motion Dale Spooner
Danville, VA, USA   USA
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1977 MG MGB
Was anything done to the head as well 2000 miles ago?

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ssmith579 Avatar
ssmith579 Steve Smith
Ventura, CA, USA   USA
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1974 MG MGB
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?

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dickmoritz Avatar
dickmoritz Platinum Member Dick Moritz
Philly 'burbs, PA, USA   USA
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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)

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ssmith579 Avatar
ssmith579 Steve Smith
Ventura, CA, USA   USA
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1974 MG MGB
Going from memory, the second valve in is exhaust. Don't shoot me if I'm wrong hot smiley

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

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chris Avatar
chris Chris Roop (RIP)
Pendleton, OR, USA   USA
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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.

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dickmoritz Avatar
dickmoritz Platinum Member Dick Moritz
Philly 'burbs, PA, USA   USA
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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 hot smiley

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... grinning smiley )

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.

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ssmith579 Avatar
ssmith579 Steve Smith
Ventura, CA, USA   USA
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1974 MG MGB
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.

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dickmoritz Avatar
dickmoritz Platinum Member Dick Moritz
Philly 'burbs, PA, USA   USA
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Bronze valve guides? Minimum 0.003 stem-to-guide clearance?

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)

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dickmoritz Avatar
dickmoritz Platinum Member Dick Moritz
Philly 'burbs, PA, USA   USA
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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)

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