Pushrods...

[BioFarmer93]

When I was a young man I built a hot rod Harley '81 shovelhead that would turn an honest 7250rpm with my big butt on it- that works out to almost exactly 140mph with stock gearing. One of the very first things I did to it was put a big cam in it and solid pushrods. I threw the hydraulics in the trash can and never looked back. Can someone explain to me why we have to use hydraulically cushioned pushrods in our engines? Other than being quieter, is there a make or break mechanical reason why this must be so? I'm sure there is something that is just SO obvious to everyone else, but I'm sitting here visualizing the the valve train and the hydraulics just seem unnecessary, even a hindrance at higher rpm...

 

[FordGuy100]

The fact that the highest factory goverened RPM of 3800 would mean nothing needed to be designed for high rpm's. It needed to be designed to maintain 3800rpm's for hours on end, which they did (anyone remember how many hours they ran an IDI at full load at the govener? It was a large number).

 

[tknomaj]

When I was a young man I built a hot rod Harley '81 shovelhead that would turn an honest 7250rpm with my big butt on it- that works out to almost exactly 140mph with stock gearing. One of the very first things I did to it was put a big cam in it and solid pushrods. I threw the hydraulics in the trash can and never looked back. Can someone explain to me why we have to use hydraulically cushioned pushrods in our engines? Other than being quieter, is there a make or break mechanical reason why this must be so? I'm sure there is something that is just SO obvious to everyone else, but I'm sitting here visualizing the the valve train and the hydraulics just seem unnecessary, even a hindrance at higher rpm...

Our Engines do not have a flat tappet cam and lifters. They are hydraulic roller lifters which are can rev to the 7250 if you have the proper valve train behind them. but our engine are made or designed for low rpms and massive torque. Our RPM limitation is not the lifters it is valve spring and rotating mass our cranks rods and pistons are heavy along with our valve train. dyoung changed the spring in his injection pup and could rev to 4k and found his valves floating some here are trying PSD valve springs but no word as of yet as to weather or not they work and how they will hold up no one has checked for binding seat pressures or weather or not they will change valve geometery . get past that hurdle and you could be there.

 

[hesutton]

Also, the hollow push rods carry the oil from the lifters up to the valves, springs, and rockers. That is the only source of lubrication for the these parts.

Heath

 

[87crewdually]

Who wants to check/adjust valve lash every oil change or anytime one starts clattering. Not me.

 

[BioFarmer93]

Who wants to check/adjust valve lash every oil change or anytime one starts clattering. Not me.

Oh yeah, I'd forgotten about that- thanks for reminding me.. I remember now, and you're absolutely right, 4 pushrods were enough. Now that I think about it, what a PITA it would be to keep manually rotating the crank for 4 times that many- I used to have to do that about every 600-700 miles because I rode the everlovin bejezuz out of that thing. Two throttle positions, wide open & idle... God must have a plan for me, because it's a wonder I'm still here! -Thanks guys-

 

[brdmh44]

Like 87 crew dually said, it's more or less strictly for less periodic adjustment. Granted a majority of your cummins are mechanical valve train, there really is no advantage in the diesel "stock" world as to any performance gains.

 

[RLDSL]

Summit racing used to list a supposed high performance cam for these engines , that was a solid lifter setup. I have no idea if anyone ever tried it, probably not since they quit selling them. It would seem to me that going to a flat tappet cam would be a massive step backwards from a roller cam.
If you want to try a cam change, Type 4 here on the site is getting them reground with a different profile that might be what you are really looking for. He's already done the homework on it

 

[BioFarmer93]

Summit racing used to list a supposed high performance cam for these engines , that was a solid lifter setup. I have no idea if anyone ever tried it, probably not since they quit selling them. It would seem to me that going to a flat tappet cam would be a massive step backwards from a roller cam.
If you want to try a cam change, Type 4 here on the site is getting them reground with a different profile that might be what you are really looking for. He's already done the homework on it

Nah, it was purely a theoretical question, I've been following the typ4 cam saga since the beginning. If, at some point in time I find myself building up or rebuilding an engine, I would like to get one. Until then I'll have to make do with what I have. I can't help to wonder though, why a roller (follower? -not real strong on all the little pieces names) couldn't still be employed sans the hydraulics.. (I know... All the reasons previously mentioned) Thank you to everyone for your responses

 

[rjjp]

You can get a non hydraulic roller set up, but all the ones I've seen were in old war birds.

 

[Black dawg]

solid roller cams make big power. when I build a new motor for my turbo truck it will have solid lifters.

 

[RLDSL]

Nah, it was purely a theoretical question, I've been following the typ4 cam saga since the beginning. If, at some point in time I find myself building up or rebuilding an engine, I would like to get one. Until then I'll have to make do with what I have. I can't help to wonder though, why a roller (follower? -not real strong on all the little pieces names) couldn't still be employed sans the hydraulics.. (I know... All the reasons previously mentioned) Thank you to everyone for your responses

THere are non hydraulic roller lifters available and I'm sure that you could find one to fit in the holes and match the pushrods...but, then you would have to completely redesign a cam profile to match the setup. Hydraulic cams and solid cams are profiled completely different. Hydraulic cams are profiled to compensate for the height loss and timing differential due to the compression of the spring loaded hydraulic piston in the lifter. If you simply put solid lifters on a hydraulic cam you would be kissing pistons with valves. There really is no performance loss with a hydraulic cam at the low rpm range that these engines run in. The only time a solid would benefit is on MUCH higher RPM engines where the compression time of the hydraulic piston in the lifter starts to become an issue. I think it would be safe to say that the profile Russ had worked up is probably a pretty safe bet. You wouldn't want to get too aggressive with the profile or you would wind up with overlap issues that simple wouldn't play nice with the diesel design. You can get away with a lot more with a gasser

 

[BioFarmer93]

THere are non hydraulic roller lifters available and I'm sure that you could find one to fit in the holes and match the pushrods...but, then you would have to completely redesign a cam profile to match the setup. Hydraulic cams and solid cams are profiled completely different. Hydraulic cams are profiled to compensate for the height loss and timing differential due to the compression of the spring loaded hydraulic piston in the lifter. If you simply put solid lifters on a hydraulic cam you would be kissing pistons with valves. There really is no performance loss with a hydraulic cam at the low rpm range that these engines run in. The only time a solid would benefit is on MUCH higher RPM engines where the compression time of the hydraulic piston in the lifter starts to become an issue. I think it would be safe to say that the profile Russ had worked up is probably a pretty safe bet. You wouldn't want to get too aggressive with the profile or you would wind up with overlap issues that simple wouldn't play nice with the diesel design. You can get away with a lot more with a gasser

OK, this is fascinating- as I understand your above statement, and assuming that the length of pushrod was modified to compensate for the change in length of the new non-hydraulic roller lifter, one would still have to modify the lift duration of the cam (I'm assuming on the opening side) because that little piston compresses THAT much?

 

[rjjp]

OK, this is fascinating- as I understand your above statement, and assuming that the length of pushrod was modified to compensate for the change in length of the new non-hydraulic roller lifter, one would still have to modify the lift duration of the cam (I'm assuming on the opening side) because that little piston compresses THAT much?

Yes, Think of setting the valve clearance on a non hydraulic setup, how excessive can you're clearance be before it runs like crap? Our hydraulic setup, in effect adds valve clearance when it compresses, then takes it up when it refills while it's at the bottom of it's stroke. If you used a solid lifter with a hydraulic cam the valve would open faster and further, then close later.