Push Rod Selection...

[elks]

So in my other thread I have selected a replacement tocker are with same ratio as what I had prior to the failure. I am replacing my push rods with the new rocker arms. The motor only had around 100 miles on it when the rocker failed. From that 100 miles I can see a perfect wear line on the valves. Nice and centered in the middle etc. I was using stock push rods. I am keeping the same lifters/cam and just replacing the rockers. If I use the same ratio rockers, can I use the same length push rod? Or do I need to install the new rockers and actually spec a new pushrod? Even though the old set up was perfectly aligned? Also what are the specs on a stock chevy 350 push rod... 7.8000 long by 3/16" diameter?


Thanks

 

[454Sub]

If the wear line is in the dead center of the valve and your sure, then use the exact same length pushrods as you had before. Now, on a motor on the lower end of the performance spectrum, such as what most of us build, pushrod length isnt exactly hugely important. Im not saying if the roller tip is rolling off the edge of the stem type drasticness it wont matter, but a hair to the inside or outside wont kill anything. Now on a high HIGH performance engine that will spell quick death.

 

[dyeager535]

I would measure them to be on the safe side. It has been proven that differences between rockers, even of the same ratio, exist. It's not something difficult to do, but I could understand wanting to buy both at the same time.

Normally you can just buy replacement pushrods singly, if you have a bad one or two, just replace those IMO, especially at 100 miles. Lay them on a piece of glass and roll them. If they aren't straight, you'll see it. Same as a pool cue.

 

[diesel4me]

I always assumed roller rockers were the "best" and would last forever,having roller tips and some types with the needle bearings in the pivot shafts instead of the ball studs-,but more than one drag racing guy I talked too said they are only good for so many hours,then are "junk",and they replace them every season,if not sooner--and wouldn't reccomend them for a daily driver on street use!.....

I've seen more than one engine with them have problems at low mileage with them...I see no reason to use them on the street really..I've had maybe 1 or 2 stock rocker arms break on small blocks in my 36 years of owning them..

 

[dyeager535]

Personally I don't see aluminum in rocker applications...many performance modern valvetrains are asking a LOT from the rockers, and IMO aluminum, other than for weight, is a poor choice for longevity if it's a pretty harsh load. All sorts of stuff is made out of AL, I understand that, but I'd expect AL to have far more problems with load over time than steel in a valvetrain application.

I suspect, as in the original problem here, that cheap rockers are used that don't last. I've got ~10 years on my comp steel full rollers, and not a problem to be seen yet. Not a ton of miles of course, and not a ton of load on them due to mild cam, but they have lasted for what I've needed them for.

Additionally, some (many?) are rebuildable, and if being used hard (I don't think that is the OP's use) I would certainly expect to need to rebuild them every season. If I was racing, there are a lot of things I'd tear down and measure/replace every season no matter what. Asking things, even such as cranks, to last indefinitely when pushed for multiple entire racing seasons, is ridiculous and foolhardy IMO. This is why trying to race on the cheap costs in the long run. Scattered motors happen from trying to save a few bucks.

Metal of any type, in any application, becomes fatigued when pushed past it's limit, and it *will* fail. And for the cost of full rollers, vs the benefit? For the average vehicle, full rollers are nowhere near enough gain to be worth it in terms of cost, performance or longevity.