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Why did I bend a pushrod?
#849283
11/08/10 11:22 PM
11/08/10 11:22 PM
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Joined: May 2009
Posts: 834
Missouri
galen
OP
super stock
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OP
super stock
Joined: May 2009
Posts: 834
Missouri
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Today I really needed a stress break so I took the car for a short drive. Drove around a little while and warmed everything up good. Ran it up to about 7200 through 1st and 2nd. Felt something. Backed out heard the miss and clatter. So far I have pulled the rockers. One lash cap is MIA. Pushrod is bent but still in place. Running offset lifters on the intakes and the correct amount of threads on adjusting screws. No galling, adjuster is ok. Good wear pattern on other lash caps. Going to pull the valley cover in the morning to check the lifter. Failure was #1 intake, 440-1s, Harland Sharps, Cam is not real radical. 263/270at.050. .690-lift. #1 cylinder leakdown ok. Springs 230#seat. I am running a smith brothers .083 wall 3/8 pushrod. What should I look for? Is it a pushrod strength issue. I had 2500 miles on it before but always shifted at 6800, this is the first at 7200.
Last edited by galen; 11/08/10 11:23 PM.
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Re: Why did I bend a pushrod?
[Re: galen]
#849284
11/08/10 11:28 PM
11/08/10 11:28 PM
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Joined: Jan 2003
Posts: 8,027
Tulsa OK
Bad340fish
master
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master
Joined: Jan 2003
Posts: 8,027
Tulsa OK
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Could the lash cap have come dislodged and cuased a piston to valve issue? Sorry to hear about the damage! Kind of makes a stress reliever go the wrong way.
68 Barracuda Formula S 340
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Re: Why did I bend a pushrod?
[Re: Bad340fish]
#849285
11/08/10 11:40 PM
11/08/10 11:40 PM
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Joined: Dec 2008
Posts: 1,200
UK
602heavy
pro stock
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pro stock
Joined: Dec 2008
Posts: 1,200
UK
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Not saying it's you're problem but never had much luck using .083" pushrods in an RB when exceeding 600lb spring pressures , those .145" walls are belt & braces. Maybe go find another stress reliever.  , just kidding. 
Last edited by 602heavy; 11/08/10 11:45 PM.
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Re: Why did I bend a pushrod?
[Re: galen]
#849287
11/09/10 01:49 PM
11/09/10 01:49 PM
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Joined: Aug 2003
Posts: 43,200
Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,200
Bend,OR USA
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I had a Smith Bros 3/8 .083 wall heat treated pushrod break in two pieces during a dyno test at 5600 RPM, it knock the top of the roller lifter off, bent the pushrod beside it and ended up dropping into the lifter bore gauging it and the cam lobe  I had Smith Bros custom make them, told them all about the motor specs, spring pressures, intended RPM and so on I help some other local racers that own a dyno, they had one of there Smith Bros pushrod break the top off of one during a dyno test also  I replace my Smith Bros with a set of seies 3 Manton .120 wall that Terry Manton recommended and that motor made 8 more HP at 300 RPM higher during the next dyno test, A,B,A after fixing the motor Smith Bros did replace the two bad ones free but didn't offer any other help on replacing or fixing the bushing, lifters and camshaft ( I didn't ask them to either  )  
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Why did I bend a pushrod?
[Re: galen]
#849288
11/09/10 03:58 PM
11/09/10 03:58 PM
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Joined: Mar 2008
Posts: 5,746
Ontario, Canada
Dodgem
master
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master
Joined: Mar 2008
Posts: 5,746
Ontario, Canada
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Yea I have bent a couple and am going to a .120 wall next year for my roller cam. My last one went sitting idling in tech line last TT (for me) day and what a racket!! Made enough noise to be a kicked rod! In with a spare and off for some TT fun. Usually intakes too with that big offset!
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Re: Why did I bend a pushrod?
[Re: galen]
#849290
11/09/10 05:57 PM
11/09/10 05:57 PM
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Joined: Nov 2004
Posts: 3,544
Syracuse,NY
CompWedgeEngines
master
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master
Joined: Nov 2004
Posts: 3,544
Syracuse,NY
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No, lifter failed first, then out went the lash cap and subsequent issues. Not sure though if it simply was a catastrophic lifter failure, or something else that cause a lobe failure, but I'd put my money on bad lifter.
RIP Monte Smith
Your work is a reflection of yourself, autograph it with quality.
WD for Diamond Pistons,Sidewinder cylinder heads, Wiseco, K1 rods and cranks,BAM lifters, Morel lifters, Molnar Technologies, Harland Sharp, Pro Gear, Cometic, King Engine Bearings and many others.
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Re: Why did I bend a pushrod?
[Re: Cab_Burge]
#849292
11/09/10 11:41 PM
11/09/10 11:41 PM
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Joined: Dec 2007
Posts: 10,542
BROOK PARK, OH
WILD BILL
Senior Member of the Junior Dragster Club
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Senior Member of the Junior Dragster Club
Joined: Dec 2007
Posts: 10,542
BROOK PARK, OH
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I just hope that's all it is and you can get it back together with out much pain 
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Re: Why did I bend a pushrod?
[Re: Bob_Coomer]
#849295
11/10/10 12:02 AM
11/10/10 12:02 AM
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Joined: May 2009
Posts: 834
Missouri
galen
OP
super stock
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OP
super stock
Joined: May 2009
Posts: 834
Missouri
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Quote:
Also, Dont dismiss a tight valve guide. I have seen them be a hair to tight and something's gotta give. 
Thanks Bob, I will check that also. I am going to pull it out at this point and tear it down.
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Re: Why did I bend a pushrod?
[Re: 383man]
#849297
11/10/10 09:53 AM
11/10/10 09:53 AM
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Anonymous
Unregistered
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Anonymous
Unregistered
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Hard to beat Crower lifters marsh performance aka Moparts Connection-- board sponsor has them in stock--The Comps are JUNK
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Re: Why did I bend a pushrod?
[Re: Old School]
#849298
11/10/10 11:24 AM
11/10/10 11:24 AM
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Joined: Oct 2007
Posts: 4,206
New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,206
New York
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If there's any question about "is it enough?":
1. biggest possible improvement is to go larger diameter until it won't fit - there is no 10mm or 13/32" OD commercially available, but it would help if 7/16" won't fit.
With same .120" wall, and rating 3/8" as 100 units for a base:
10mm = +21%
13/32" = +36%
7/16" = +80%
1/2" = +198%
2. increased wall thickness is far less effective, only do this when #1 is not possible.
Boffin Emeritus
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Re: Why did I bend a pushrod?
[Re: polyspheric]
#849299
11/10/10 01:37 PM
11/10/10 01:37 PM
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Joined: Mar 2006
Posts: 9,910
Eighty Four, PA
B G Racing
master
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master
Joined: Mar 2006
Posts: 9,910
Eighty Four, PA
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Quote:
If there's any question about "is it enough?":
1. biggest possible improvement is to go larger diameter until it won't fit - there is no 10mm or 13/32" OD commercially available, but it would help if 7/16" won't fit.
With same .120" wall, and rating 3/8" as 100 units for a base:
10mm = +21%
13/32" = +36%
7/16" = +80%
1/2" = +198%
2. increased wall thickness is far less effective, only do this when #1 is not possible.
Easy comparo for pushrod wall thickness: it's pretty close (never exactly) to new ÷ old.
.120" ÷ .083" = 45% stiffer
45% stiffer,if only I duplicate that.Bigger is always better,so I'am told 
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Re: Why did I bend a pushrod?
[Re: polyspheric]
#849301
11/10/10 02:55 PM
11/10/10 02:55 PM
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Joined: Feb 2007
Posts: 970
Backwater, PA
bwdst6
Bob George Racing #1 Fan
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Bob George Racing #1 Fan
Joined: Feb 2007
Posts: 970
Backwater, PA
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Quote:
2. increased wall thickness is far less effective, only do this when #1 is not possible.
Easy comparo for pushrod wall thickness: it's pretty close (never exactly) to new ÷ old.
.120" ÷ .083" = 45% stiffer
That estimation isn't even close. I'm calculate that with a .375 OD pushrod going from a wall thickness of .083 to .120 (or an ID of .209 to .135) the increase stiffness is just 9%. And considering the additional mass one would be adding to the valve train I would say it isn't worth it!
moment of inertia = pi(OD^4-ID^4)/64. ID^4 is the killer.
Last edited by bwdst6; 11/10/10 02:59 PM.
This post is available in double vision where drunk.
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Re: Why did I bend a pushrod?
[Re: bwdst6]
#849302
11/10/10 03:21 PM
11/10/10 03:21 PM
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Joined: Oct 2007
Posts: 4,206
New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,206
New York
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You're right - I typo'd it!
What do we learn from this: don't rely on memory, if you actually data.
Thanks.
Boffin Emeritus
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