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Beautiful Drive Ends with Pushrod Failure

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cobrapatrol Avatar
cobrapatrol Gold Member Jim Harris
Quartz Hill, CALIFORNIA, USA   USA
I finally got my 69 TR6 registered for the road and have put 200 miles on it (the first in 26 years), mostly mild around town driving and a 75 mile round trip commute to work. The engine has been running beautifully. I decided to take it out on my local canyon roads for a 30 mile tour and some pictures that I could share with you all. I am quite sure I have never exceeded 4500 RPM since building the engine. After about 20 miles I stopped for some pictures and when I started the engine it began running rough and backfiring out the exhaust. I limped down the road a couple of miles to where I could get cell service and called AAA for a tow.

Back at home I pulled the valve cover and discovered that the #1 exhaust pushrod was broken at the top cup. These were new pushrods, lifters, and cam (Kent Road 83) and I had re-torqued the head and re-set the valve lash after the first few miles as a standard precaution. The cam is mild and I had clearance checked all the valve gear on assembly. I checked the broken pushrod for any signs of rubbing or contact but found nothing. About 60% of the top of the socket, where it cups the rocker ball, was cleanly cracked off. I have not yet found the pieces with a magnet.

So what could cause a brand new pushrod to fail in this way? Has anyone seen this type of failure?

It pains me to show off my newly restored TR and in the same breath talk about its failure but there it is!



Jim Harris
Quartz Hill, CA

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Perdido Avatar
Perdido Gold Member Rut Rutledge
Tuscaloosa, Alabama, USA   USA
Jim,
Beautiful TR6! It looks like it just a bad push rod...stuff happens. I would call the mfg to find out if they have had any issues and see what they say. I also pre lube the top end of my engines after a build or a long time sitting up, just pour oil over everything.
Rut

poolboy Avatar
poolboy Ken D
Sandy Hook, Mississippi, USA   USA
The car looks great, Jim.
What valve lash is called for with that cam ?

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Perdido Avatar
Perdido Gold Member Rut Rutledge
Tuscaloosa, Alabama, USA   USA
In reply to # 1498606 by poolboy The car looks great, Jim.
What valve lash is called for with that cam ?

Looks like .022 and .024, but Kent doesn’t show a Road 83 that I could find...this is just the most common setting for their fast road cams.
Rut

titanic Berry P
Albany, Oregon, USA   USA
The broken push rod might be the effect of another problem. Possibly coil bind or a valve seizing in a guide from inadequate clearance (especially likely if new bronze guides were fitted).
Berry

cobrapatrol Avatar
cobrapatrol Gold Member Jim Harris
Quartz Hill, CALIFORNIA, USA   USA
I had the clearance set at the recommended 0.016, which should have been plenty. Kent no longer lists the cam as such but the cam came from Moss in a Kent box with Kent instructions. I bought it from Moss under the part # 838-042, mild upgrade 0.288 lift. Suffice to say that the valve train was probably not overwhelmed by a high-lift cam. Interesting point, titanic, about the bronze valve guides (installed with seals during the head rebuild). Since the engine had been stopped warm (not hot) after 20 miles and left to sit for 10 minutes while I took some pictures I suppose it's possible that the valves could hang in an expanded guide. But I thought in most cases that a pushrod should bend instead of breaking. The rod is still straight.

Thanks for nice comments on the car itself. I was really hoping to be posting about its coming out party, not its first mechanical failure! But I know that's the life of any LBC owner.



Jim Harris
Quartz Hill, CA

Perdido Avatar
Perdido Gold Member Rut Rutledge
Tuscaloosa, Alabama, USA   USA
Jim,
The machine shop should be able to verify the clearance on the valve guides which need to be a few thou over for bronze vs cast iron. That sounds like the most plausible explanation.
Rut

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grubscrew Avatar
grubscrew grub screw
The suburbs of, Winfield, Maryland, USA   USA
In reply to # 1498602 by cobrapatrol ... Has anyone seen this type of failure?

Yep. Suffered a broken push rod when running at highway speed in my 70 Spitfire in about 1972.

Clean break. I fished out the pieces, installed a new push rod, set all valve lash, and problem solved.

Just a random defect in the factory-original part.



Dave
1970 Spitfire Mk3
FDU 78359L
34/11 (Jasmine yellow/Black interior)

1962 Triumph TR3B
TCF 575L
Signal Red/Red interior

cobrapatrol Avatar
cobrapatrol Gold Member Jim Harris
Quartz Hill, CALIFORNIA, USA   USA
Thanks all

Later today I will check compression on all cylinders, in case there is any systemic valve issue, and watch the valve action closely. After that I need to find the metal fragments, and since I can't seem to find them in the top end I will have to pull the pan.



Jim Harris
Quartz Hill, CA

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South San Frncisco, california, USA   USA
well, on the bright side, only one pushrod is broken...
it looks like beautiful motorcar, well kept. did you have as much
fun as I did getting it re-registered as I did here in sunny calif?
mine after 21 dormant years, yours 26?

I guess to be sure about valve to guide clearance you have to
take much apart, though I have heard there is a method to removing valve spring
and reinstall w/o removing head.
would get that pushrod replaced and run engine when done w/out cover and observe
action of rockers and rods... maybe it is just annoying anomaly...
where are the broken pieces? vexing, very vexing...
good luck and sorry.
mmm Quartz Hill, elevation 2497 feet... mmm..mmm. no that can't be it...,...
wes

cobrapatrol Avatar
cobrapatrol Gold Member Jim Harris
Quartz Hill, CALIFORNIA, USA   USA
Wes

I'm just down the road from Willow Springs raceway, can see it from my house. The whole area is called "the high desert" because the bottom of the valley is at 2200 ft. Makes for some lovely canyons, though!

Yes, the Ca title and registration was problematic, even though I used AAA as a buffer. It took four visits and several "Statement of Facts" from the PO. There were two owners since the car was last on the road so the title had changed hands with no update since original. The TR was a basket case when I got it. But at least I didn't have to surrender my blue plates. I hope to have them re-instated under DMV policy VIN 2009-20 but I'll wait until after I'm retired next February because only DMV can handle that transaction.

Sounds like you had "experiences" too.

Jim

A couple more pictures, the first from Sept 4th, then Nov 16th



Jim Harris
Quartz Hill, CA



Edited 1 time(s). Last edit at 2017-11-18 12:49 PM by cobrapatrol.


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Tonyfixit Avatar
Tonyfixit Tony M
Duncan, British Columbia, Canada   CAN
No bits fell down to the lifter?

How big a bit/bits are missing?

I would not worry about valve guides too much, that should not cause this anyway, I just think you got a sub-standard push rod.

Think yourself lucky, in my case it was a valve spring 500 miles after a rebuild :-(

cobrapatrol Avatar
cobrapatrol Gold Member Jim Harris
Quartz Hill, CALIFORNIA, USA   USA
Wow, yeah, valve spring, not thanks! I hope no head/piston damage!

I've searched in the lifter wells and into the lifter cups with a magnet and my eyes with no success. The oil drain-back hole is in the next cavity back from the lifter well of the broken pushrod so I'm thinking The pieces fell into there and down into the crankcase. Obviously I will have them in hand before I start the engine. Should be two fragments based on what the pushrod end looks like.



Jim Harris
Quartz Hill, CA

Krom Avatar
Krom Paul K
San Rafael, CA, USA   USA
Jim, your car looks great. Congratulations on your rebuild. You might check into Smith Brothers pushrods. They are good quality and can make them any length you need. Do check for binding in the valve train. I had a rebuild and it included a slight decking of the head and block and a non-stock cam. Had some valve spring binding that ended up with a dose of metal particulate in my new engine...broke a rocker, not a pushrod. Got the Smith Brothers rods and a Good Parts roller rocker set and haven't had a bit of trouble since. If I was doing it, I would pull the rocker assembly and all the pushrods and lifters and be really thorough about cleaning it up. I know it is a major pain just after a rebuild, but the labor is better than polluting the bearings and the cam. Good luck. PK

glcaines Avatar
glcaines Silver Member Gary Caines
Hiawassee, Georgia, USA   USA
Beautiful car! I would really suspect a faulty pushrod as others have suggested. I would also suggest removing the entire rocker assembly to clean up, as well as the pan. Good luck.



Current: 1973 TR6 W/Overdrive

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1963 TR3B W/Overdrive
1962 TR3A
1961 TR3A
1960 TR3A
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