I think I may have bent push rods--and other issues (76 GMC W/455 Olds). Crap.

OldBlueDually

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Well Gent's, all the work into the 76 GMC dually has been worth it, but now I think I may have another unforeseen problem!! Looking for advice here, I think I am on the right path.....

Not too long after firing it up for break in, this 455 just did not have the "potato" sound that it should have with this Thumpr series cam I used. Well tonight I had it idling outside the garage and heard a LOT of valve-train noise on the drivers side of the engine and it had me scratching my head. It was a whole lotta "clicking & ticking" sound!!!!

So, I knelt down by the drivers side exhaust and she just had that deep Olds grumble, and not much cam sound. Then I knelt down by the passengers side exhaust and could hear that throaty Olds big cam sound, with a little bit of valvetrain noise on passengers side....what in the literal heck is going on here! Now, I have my STOCK rocker arms & pushrods in this engine. Thumpr cam, with 402 pound dual valve springs. Some rocker arms are a little worn on the valve stem side (shame on me for using them!!), some rockers worn on the inside pivot (again, shame on me), pushrods looked beautiful & were straight (rolled them on a nice flat surface before using).

After I put the truck away tonight, I came inside and started taking a look at pushrods for this engine, and rocker arms. Most all the pushrods I see are chromoly material, and hardened and can only handle anywhere from 300 to 350 pounds of valve spring pressure. Mine valve springs are 402 pounds as stated above. Crap. I can guarantee my stock pushrods can't handle anywhere near 402 pounds.

I found these here (not available until November!!!) that should work (higher spring pressure mentioned);

Now I need to find some good rocker arms & pivots, just unsure of what to get. Prior to doing any of this however, I need to pull the valve covers, and remove the rockers & pushrods to see whats going on. I plan to do this in the next couple of days.

With reading the above, would you guys also be looking into the valvetrain like this too? I "think" I am on the right path. I have not had this happen in prior builds with this kind of valvetrain noise.

Thanks for reading another one of my books!
 

bucket

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I'm not familiar really with the Olds engine family. Have you pulled valve covers for inspection? Hopefully your new cam isn't going flat.
 

OldBlueDually

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I'm not familiar really with the Olds engine family. Have you pulled valve covers for inspection? Hopefully your new cam isn't going flat.
Not yet, plan to tomorrow, or Thursday. I don't think the cam would be flat (man I hope not!!), as I followed the cam break in procedure from Comp Cams right to a tee...and I see no shavings, or any hint of glitter in the oil, it's still as clean as can be.

I could make that meme now too, the couple laying in bed with her saying "I bet he's thinking of other women" and me thinking "why is my 455 Olds having valvetrain noises" :Big Laugh:
 

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Pull the oil filter, cut it open. If there is any cam wear the debris will be in the oil filter.

Oldsmobile (like many other engines of those years) have non adjustable valvetrain. Meaning assuming the valve job is done correctly, the distance from the cam to rocker arm hasn’t changed from stock (milled heads, different thickness head gasket, decked block, etc) the cam base circle isn’t different from stock, if you torque the rocker bolts everything SHOULD be good. Basically, you want the lifter plunger .020-.030 depressed with the cam on the base circle.

Unfortunately, lots of variables. Comp Cams use to offer an adjustable valvetrain kit, once again the pushrod length rarely was right especially if the engine is modified.

Oldsmobile use to offer a shim kit to correct lifter preload. I’m sure Comp cams or Lunati offer them also. I’m almost positive the shims are the same as some AMC engines.

If the engine has been modified, most likely the lifter preload is excessive. Easy way to check:

Pull the plugs, remove the valve covers. remove the rocker arms and stand. Use a sharpie, paint the end of the valve stem. Reinstall the rockers/pushrods, spin the engine a few times. Remove the rockers, inspect the paint mark. Hopefully where the rocker wore off the paint is centered on the valve stem. If not, the pushrod length is wrong.

Once that is good, it’s time to lash the valves. Get the engine at TDC on #1 (both valves closed) remove the rockers and pushrod. Paint the pushrods, install the rockers and ONE pushrod. SLOWLY spin the pushrod with your fingers, while slowly tighten the rocker bolt. Stop at zero lash. Make a mark on the pushrod level with the head. Next, tighten the pushrod to spec. Make another mark in the paint. Remove the rocker/pushrod and measure the distance between the marks. Your looking for .020-.030, if it’s different you either need to mill the rocker stand, or most likely shim the stand to get the clearance right. Do that for the other 15 rockers.

If that’s too much work, call Rocket Racing, Bernard Mondello in Tennessee (STAY AWAY FROM MONDELLO IN CALIFORNIA!!!!!!) or I can give you some other Olds specialist phone numbers, any of them have Olds specific rocker arm setups.

As I’m sure you have already figured out, most speed shops/machine shops are Chevy/ford oriented. Most don’t have a clue about olds stuff. I always tell my olds buddies it’s well worth the trouble to either find a machine shop familiar with Olds, or find a shop that won’t argue about the machining characteristics of Olds engines. What works well for Chevy doesn’t work for Olds. They aren’t bad engines, as a matter of fact the 455 is the perfect truck engine. They are natural low end torque monsters, perfect for work trucks.
 

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@Matt69olds are you speaking of these guys, it says they are in Wisconsin..?? https://rocketracingperformance.com/

When you stated to paint the pushrods, you mean with sharpie like on the valve stem, correct? Would I mark the pushrod with something simple like using a steel 6" rule (flat against head top surface) to scrape the sharpie mark into the pushrod, then torque down and make another scrape, correct? Or is another tool better suited for something like this

Dam, learning stuff a bit late here. Better late than never!

Yeah, most shops don't know much about Old's engines (or Flatheads) it seems. Back when I sent off my 350 Rocket to Scharf Auto to get built, I told them exactly what kind of HP I wanted out of it.....the thing came back as basically a stock pooch, I was fricken ticked. Over $3k later for all the work done at the shop, and my dad and I did all the assembly work.
 

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I used to run an Olds 455 in a '73 Firebird. I never had any trouble with it. I think it had a 268 adv. duration Erson cam in it, with matching springs, and stock rockers and pushrods.
402 lbs of spring pressure sounds kind of high for a stock engine. What cam are you running? Is it a high compression or low compression motor.
I have been hearing alot of bad stuff about Comp cams lately...
 

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Lots of flat tappet cams and lifters getting wiped lately. I agree, that's a LOT of spring pressure for a flat tappet cam.
 

OldBlueDually

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I used to run an Olds 455 in a '73 Firebird. I never had any trouble with it. I think it had a 268 adv. duration Erson cam in it, with matching springs, and stock rockers and pushrods.
402 lbs of spring pressure sounds kind of high for a stock engine. What cam are you running? Is it a high compression or low compression motor.
I have been hearing alot of bad stuff about Comp cams lately...

I have a higher compression (stock around 9:1 to 10:1) 1969 Olds 455 with C heads. Here below is the cam that I have.


Here are the springs that are supposed to be installed with the above camshaft.

The above is why I "think" I am hearing noise. I am starting to think my pushrods are bent, or bending, or flexing.....something is wrong. I plan to remove valve covers tonight.
 

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I'm hoping it's as simple as too much spring pressure and you just have some bent pushrods. Interesting read from Matt, I've never read up much on Olds motors. I'm definitely curious to hear your findings
 

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The cam is a little long for a truck in my opinion, but not much. I am not sure about the springs, I didn't see where it spec'd that spring anywhere. It sounds like it should be a good engine. I am curious what you find out.
 

OldBlueDually

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@TotalyHucked I am hoping for the same too! I will be certainly doing what Matt stated above for sure!

@85K304SPD this baby will be a cruiser, nothing more. It may pull the camper a bit to local area's. I love the Thumpr sound, hence the reason I chose that cam. As for where the site mentions springs.....they have changed their site. It used to have tab next to specifications that stated "suggested parts" and those springs were listed there. I had to go back to my e-mails to find my orders for those springs.

Now I wish they had listed a suggested pushrod too. From what I have read, most pushrods can only handle up to 350 pounds of pressure. Wonder what my stock ones would be rated for then??
 

85K304SPD

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I have a "stage 3" cam in my camper truck, 76 F250 with a 460. It sounds good, but I wish I would have put a little shorter duration one, for more low end, and maybe better mileage. Haha Maybe go from 7 mpg to 10. I do remember the Olds pushrods being pretty skinny. I dont think that they flex, just bend. If they are bent, and you are confident with the valve springs, you should be able to get some larger, stronger pushrods from somewhere.
There is always a way...
 

Bextreme04

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The cam is a little long for a truck in my opinion, but not much. I am not sure about the springs, I didn't see where it spec'd that spring anywhere. It sounds like it should be a good engine. I am curious what you find out.
Its a thumper cam, so they have big duration and lower lift in order t ogive it a "lumpy" sound without actually making the dynamic compression too low. It replicates that "full race" lumpy idle without all the downsides of having an actual racing cam and crazy high compression on the street. They are generally considered a show, not go, type of cam.

I have a higher compression (stock around 9:1 to 10:1) 1969 Olds 455 with C heads. Here below is the cam that I have.


Here are the springs that are supposed to be installed with the above camshaft.

The above is why I "think" I am hearing noise. I am starting to think my pushrods are bent, or bending, or flexing.....something is wrong. I plan to remove valve covers tonight.

I'm reading that spring spec as 402lb/in of spring rate. Since you have less than 0.50" lift on that cam, you shouldn't have anywhere near 400lbs of spring pressure open, unless you have 200lbs of seat pressure. Who set up the springs and installed height? Did you actually measure seat pressure and open pressure?

The comp cam spec calls for an installed height of 1.700". At that installed height you would have a seat pressure of 115lbs. With your cam, that would then give you an open pressure of:
Intake: 115lbs + (0.491*402) = 312lbs
Exhaust: 115lbs + (0.476*402) = 306lbs

Which puts you right in line with what the chromoly pushrods can handle. Hardened isn't for strength. You need the hardened pushrods if you are running guideplates. Are the stock pushrods 5/16"? I see that several companies make valvetrain kits to convert to full roller rockers with guideplates and 3/8" pushrods.
 

Bextreme04

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It is also worth noting that those are dual springs. It has been mentioned on a few sites that it is a good idea with the issues with lifters and flat tappet cams going flat lately, that it is a good idea to do the cam break-in with the inner springs removed to give the cam and lifters the best chance of living. Once cam break-in is complete, you can then reinstall the inner springs.
 

OldBlueDually

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@Bextreme04 I did all this work myself, and did not actually measure installed height. In hindsight I should have done a lot more than just degreeing this cam and thinking all else was ok....because it wasn't.

Also, as I stated above I followed break in to a tee from Comp....no inner valve springs, engine oil not primed, lifters not soaked in oil, used cam break in additive, ran it at the RPM's stated for the length of time. After that I dumped oil, changed filter and put in fresh oil and added a zinc additive...and also installed inner springs.

Took off drivers side valve cover tonight, pushrods look good, but I have a bunch of very loose rockers. So, the work continues to redo the rockers, and machine pivots down.

I will probably still put in those heavier 3/8 pushrods from the link above also, just to be sure.
 

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