General Category > GM Tech Questions and Answers

Flat tappet or roller? Solid or hydraulic?

(1/2) > >>

Cool53:
Myth-Oil is the biggest cause of flat tappet failure so I really need to run a roller cam.

Myth-Solid cams are a pain because they require constant adjustment.

The truth about flat tappet failure relates more to lifter quality than zinc content in oil. People talk about zinc but are never specific about whether dialkyl or diaryl zinc. If you don't think oil is better now than it was in 1963 you need to reexamine your thinking.
I never sell a roller cam if I can help it, and in the last 40 years I have had no failures. Lifter face quality is the issue. I have been hand polishing lifters since the quality has dropped off, but now Johnson Lifters is back in business the issue is moot. Their lifters are perfect, and for a few dollars more you can get them with a tiny hole in the face that has been made through EDM to supply more oil. And CompCams and others offer a nitride coating for extra charge to keep the cam bumpy. Plus, a failed roller lifter causes a lot more damage than a failed flat tappet.

As far as solid versus hydraulic I like the little extra response of a solid. The only time I ever need to adjust my valves often was when I was using low priced roller rockers. They have small trunnions and wear, which isn't good, so I've switched to Ultra Pro Magnum rockers from Comp, no more issues. With a hydraulic cam you have to have quite a big of wear before you hear a loud lifter, with a solid you'll notice an issue right away. And let's face it, it's like changing an oil filter and nit cutting it open to check for metal, you really should pop the valve covers on a performance engine to check on things.

I know this subject will raise some questions. Wait until we get to carburetors! Some of you will want to punch me in the nose!

themoose:
Jef
Ware issues aside, isn’t one of the advantages of a roller cam the fact that you can have a much more aggressive lift-curve capability as compared to a flat-tappet cam. In order for a flat tappet cam to generate as much lift as a roller, it requires more duration so the flat tappet lifters would actually dig into the lobe flank if the lobe is designed too aggressively. Roller tappets don’t suffer that problem so the cam manufacturer can put much more lift into a roller cam lobe. Not only that, from what I understand  if you’re using the Chevy Fast Burn/Vortec heads like I am the roller profile can be designed to hold the valve open longer above 0.200-inch tappet lift which can really help increase airflow during the time that the cylinder head offers the most potential flow. As you said the subject of camshafts can always generate a lot of discussion and I’m looking forward to the discussion.

You raised the subject of cutting open the oil filter to check for metal debris which brings to mind another question…..What do you recommend for brand of oil filter. Back in my early days we always used Fram filters but from what I’ve seen recently people have had all sorts of problems with them. I’m not sure if it’s urban legend of fact so I thought I’d ask your opinion

Moose

MIDROAD:
I've used both roller and flat tappet cams with success. Here in Australia we don't have the low zinc oil problem so much.
I agree that lifter quality is a problem so you need to buy the best quality you can afford.
The major reason I've found for lobe failure (apart from poor break in procedure) is overly aggressive valve springs. If you want to run a 8000 RPM SBC on the street be prepared for regular teardowns and repairs.
               Mike.

Cool53:
Hey Moose. I guess I missed making my point once again. I absolutely prefer a roller, a solid roller. But the point I was supposed to be making was that it is not necessary to run a roller. Most of my customers are on a budget and could use the extra money a roller costs for other parts.
Everything you said is absolutely correct. But lifter quality in rollers is a problem now,too.mtoo many offshore parts. And if you are going to make big rpm then going the route of bushing the roller is a must. By the time you get the right valve springs, and possibly a high rev kit, you are squeezing that cam really hard. The only way needle bearings work properly is when they are separated. When they touch they are going in different directions, which creates a ton of friction, wear, and brinneling.
And our friend from down under is absolutely right. Most people are really not sure where their springs are. I have a spring tester that fits right on a rocker with everything still assembled so I can check check springs on a customer's car or while at the track on my own stuff. But let's face it, with street vehicles most engines don't even have TDC correct.
The high load issue of springs with seldom driven cars is also tough on cam bearings, so I use coated bearings everywhere.
Low speed, like idle speeds, are rough on roller lifters because of the camshafts dramatic profiles. Roller lifters are tested for longevity at 80 rpm.

themoose:
Jef

MIDROAD mentioned possible cam failure being caused by high tension valve springs which brought to mind another question. What do you think of the beehive valve spring setups and will you use them on you new 362?

Moose

Navigation

[0] Message Index

[#] Next page