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Beautiful Drive Ends with Pushrod Failure

Moss Motors
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cobrapatrol Avatar
cobrapatrol Gold Member Jim Harris
Quartz Hill, CALIFORNIA, USA   USA
I don't see any bits or shavings in the top end, everything is pristine. I think the pushrod broke off two bits based on the fractures I can see. I will be getting into the oil pan today.

I did a compression check last night. It was the #1 cylinder that had the broken pushrod. The results of the check were:

130 140 150 150 145 145

So the #1 cylinder is suspect. It leaks down quicker that the rest also. Still, not bad enough to warrant pulling the head immediately. I think I will run it after getting the metal bits out and see how it goes, then do another compression check.



Jim Harris
Quartz Hill, CA

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Tonyfixit Avatar
Tonyfixit Tony M
Duncan, British Columbia, Canada   CAN
How many miles on this engine? I would not worry about that 10 -15 psi being down at this stage.
Unless you have grave doubts about whoever did the head work, I cannot see a connection between your broken push rod and the rest of the valve gear.

Do you feel lucky enough to fish in the oil pan with a magnet on a stick?

Consider making or buying a magnetic oil drain plug. If you make one, choose to use a Hex headed pipe thread plug and get away from the wretched square plugs.

South San Frncisco, california, USA   USA
what if the ball end of rocker was off-center, not aligned, bent,
or the pushrod failed to rotate, as they tend to do in action...
also, vendors state under some conditions the opening in head
for pushrod needs opening up slightly as larger diameter p rods
can hit the openings ...
cam pushes tappet, pushes rod, pushes rocker, pushes valve stem top...
anything out of alignment, or if jammed...a break in pushrod cup seems
the weak point.
would the broken pieces if not in the cups of tappets, migrate into sump,
sink to bottom...and sit harmless...
hopefully any bit of broken p rod is too large to make it past oil pump filter...
as simple as it seems, suspect everything...
wes

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South San Frncisco, california, USA   USA
Jim, please report back what you find. Who can say
same thing wont happen to them? Curious if and
where you find the pushrod bits., very nice car...
wes

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

I took the pan off yesterday afternoon and immediately found one piece in the pan. Nothing came out in the oil. Nothing in the pump screen. Good sign that there's no small bits or shavings to speak of. Matching the piece up to the pushrod shows that the other piece should be larger. I wonder if it could be lodged between the cam and the oil return hole. I have put a magnet down both return holes but have not had any luck. Now I am waiting for my friend Dave to come over and help, he's kind of OCD and will help me ferret out this other piece.

Other than that everything looks good in the crankcase.

Thanks for asking! I will report back for sure.

Jim



Jim Harris
Quartz Hill, CA

POW Peter Wirth
HEBRON, NH - New Hampshire, USA   USA
I hope you find the rest of it. I guess it could have spent some time bouncing around in the cover before the engine got shut down. It's highly unlikely I suppose but could it perhaps have found it's way into the breather pipe.

Regarding breaking in the first place. If the ball on the rocker was a bit oversize or the cup on the push-rod was a bit under size the mating parts could have been working to spread the cup end until a piece snapped off.

Tonyfixit Avatar
Tonyfixit Tony M
Duncan, British Columbia, Canada   CAN
I am curious to see what broke and what you found, any chance of a picture?

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Darth V8R Avatar
Darth V8R Vance Navarrette
Beaverton, Oregon, USA   USA
1980 Triumph TR8 "Wedgie"
In reply to # 1498981 by cobrapatrol Wes

I took the pan off yesterday afternoon and immediately found one piece in the pan. Nothing came out in the oil. Nothing in the pump screen. Good sign that there's no small bits or shavings to speak of. Matching the piece up to the pushrod shows that the other piece should be larger. I wonder if it could be lodged between the cam and the oil return hole. I have put a magnet down both return holes but have not had any luck. Now I am waiting for my friend Dave to come over and help, he's kind of OCD and will help me ferret out this other piece.

Other than that everything looks good in the crankcase.

Thanks for asking! I will report back for sure.

Jim

Jim:

To be safe, you should measure the space between spring coils with feeler gauges when the valve is fully open. You will need 0.020" between each coil to be on the safe side.

Also, you mentioned valve stem oil seals. You need to measure the space between the bottom of the valve spring retainer and the top of the oil seal. You need 0.060" clearance for a good margin.

The DPO on my TR8 installed oil seals on the valve guides. When he started the engine they were all crushed because he had not left enough clearance. After I purchased the car I pulled the valve covers and found broken bits of rubber/plastic. Disassembled the heads and found more. Showed my machinist and he knew what it was right away. I had suspected but could not believe anyone could be so ham fisted. The engine did not originally have seals, so he popped them in without getting the valve guides cut down.

I agree with the others that a defect in the pushrod is likely, as the quality of some replacement parts is shockingly low. But I would double check the clearances to insure there was not an error in machining or installation.

All IMHO, of course.

Vance



1980 Platinum Metallic TR8, navy blue interior
Bare metal respray, Crower cam, raised compression
ported heads, modified Zenith carbs, 0.060" overbore

Tonyfixit Avatar
Tonyfixit Tony M
Duncan, British Columbia, Canada   CAN
Good pointsmade by Vance.

I agree on the shockingly low quality of many replacment parts, and how vowed not to replace parts for the sake of replacing, or sorce OE parts (even used) ifpossible.
Remember my valve spring story :-(

I missed that you had valvestem seals. I also have had bad luck with these causing rapid valve guide and stem wear.

Sorry :-(

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cobrapatrol Avatar
cobrapatrol Gold Member Jim Harris
Quartz Hill, CALIFORNIA, USA   USA
I finally had time today to get the head off to search for the missing part of the broken pushrod. And there it was, lodged in the second oil return passage back from the front. The fragments are all cleanly fractured and can be pieced back together with nothing missing so I feel pretty good that there will be no loose bits left in the engine. There is a shiny band on the inside of the cup area where it looks like the rocker pivot ball contacts in the cup, about 1/4 of the way down from the top. It looks like there's only about 0.020" wide contact area. I took a look at my old (original) pushrods and they have a shiny contact patch that goes all the way down. So the surface contact area is much bigger. It's possible that the cups of the new pushrods are slightly too small, causing much greater pressure across the smaller contact area. All of the other pushrods have the same wear pattern. There's only 230 miles on the engine since I put the new pushrods in.

I double checked for any contact between the pushrod and the rocker (behind the pivot ball) but that would only occur with much more extreme cam geometry. I also verified that my valve spring clearance at full lift was more than 0.060, so coil bind was not going to happen. The rest of the engine looks very clean although there was a small bit in the oil pump pickup. I've got to say that I'm not impressed with the original pump siphon or the small screen inside of it so I'm going to take the opportunity to install the later model pump with the big screen bulb on the bottom.

I will be contacting the source of these pushrods (Moss).



Jim Harris
Quartz Hill, CA


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titanic Berry P
Albany, Oregon, USA   USA
I noticed a shiny spot near the top of the push rod. Any chance that the push rod was rubbing against the head? There is not much clearance and it might be possible that the replacement push rods are slightly larger in diameter than the originals or the geometry changed with the new cam.
Berry

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

Good thought but I think it's just that once the pushrod broke it fell out of the rocker arm pivot (having virtually no socket left) and was rubbing on the side of the head with the cam still pushing it up and down. None of the other pushrods had any sign of rubbing. When I pulled the rocker cover the pushrod was kind of wedged to the side, leaning against the head.

Jim



Jim Harris
Quartz Hill, CA

POW Peter Wirth
HEBRON, NH - New Hampshire, USA   USA
In reply to # 1499002 by POW I hope you find the rest of it. I guess it could have spent some time bouncing around in the cover before the engine got shut down. It's highly unlikely I suppose but could it perhaps have found it's way into the breather pipe.

Regarding breaking in the first place. If the ball on the rocker was a bit oversize or the cup on the push-rod was a bit under size the mating parts could have been working to spread the cup end until a piece snapped off.

The push-rod cups COULD all be undersized but another thing to consider would be the ball-ends of the adjusters like I mentioned above. I'm not sure if this can happen but was thinking if those are original it's possible they spread, kind of in the same way our feet tend to get wider with age. When re-assembling used push-rods to used rockers there is a reason it's suggested they mate to the same partners. If Moss gets to look at the rods and declares them in spec, I'd consider getting brand new adjusters to go along with them. - Pete

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

Thanks for the idea, it's easy enough to check with a micrometer. Although the engine only has 34,000 miles on it from new. I tend to distrust modern metallurgy and production tolerances on these repro parts a lot more. The easiest solution is to just put the original pushrods back in. I only changed them during my engine overhaul because the original cam and lifters were pitted and spalled. I will have more after I can confer with my friend Dave, who's profession centered around breaking metal.

Jim



Jim Harris
Quartz Hill, CA

Tonyfixit Avatar
Tonyfixit Tony M
Duncan, British Columbia, Canada   CAN
I did wonder from the beginning why you did not use the original push rods.

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