Roller cams, cons.....pros???
 

Ever wonder why the 575SCI runs a flat tappet cam? I sure do, and never got a real answer from the Merc rep at the Miami show.

Late last season, I had destroyed a motor from a roller lifter tie bar breaking and the roller got loose at 5500 and totally ruined the entire long block.

Today I had the other motor torn down for inspection and found a cam lobe going away because of a skidding roller. Fortunately there was no other damage. How often does this happen? I have been told that synthetic oils can cause the rollers to skid instead of spin but this motor has always been run on Kendall petroleum oil and changed every 10-20 hrs.

If Merc is still running flat-tappet hyd cams in their 575 they must be still working well. Can I run flat tappet cams in my 468" 671/Supercooler 8 lbs boost BBC?

At this point, I'm not sold on the roller cam. Seems like too many things to go wrong.

Kurt

What kind of roller?

Kurt,
Running a flat tappet cam on a S/C application does not require the same optimization of lobe profile that a N/A cam requires. The addition of forced induction negates the necessity of inertial ram and overlap that are the keys to making power in atmospheric engines. Roller lifters accommodate acceleration rates that are not possible with flat lifters, but not necessary with boost present in the induction column. V.E. numbers of 100%+ are routine with superchargers, but not directly related to cam timing.
In my experience I have yet to see a cam lobe going away due to a “skidding” roller. Burnished rollers and lobe degradation are nearly always the direct result of improper or failed valve springs. Synthetic oil is not a contributing factor. Both street and endurance racing engines routinely run roller lifters with synthetic oil successfully.
Bob

Thanks for your reply, they were Comp Cams components.

Kurt

every type of set-up has some lemons once in a while....
 

On a side note, I am doing a cam swap/ head work on my bike. At tear down and inspection, I had a roller lifter skidding on the cam lobe. Cam was ok but lifter seemed to be a little tight in the roller bearings. Must have gotten some crap in there. Initial thought was to high of spring pressure. New lifter and cam being installed and double checking spring pressure.

Might have lost rollers due to SMALL contamination or needle bearing failures...

Zack

The only "skidding" rollers I've ever seen or heard of were eventually traced to the needle bearings in the roller tips themselves.

Anybody got more info on those "needle-less" roller lifters that use a trapped oil film for the roller to run in? They look pretty cool.

Mike,
They are made by Schubeck. You can find the info here:
http://www.schubeckracing.com/rollerx.html
Bob

The Schubeck lifters seem to be the answer to the sticky roller problem and I like their method of retaining the lifter in a Mark IV block. Nice stuff!

I just got a call from my engine builder and he said everything else looks great. I guess I'm lucky that a little preventative maintenance found a big potential problem :D

Back to the 575 SCI, I find it interesting that Mercury feels the flat-tappet hyd cam is the way to go on this application. Phil @ Lip-Ship tell me that even Zul retains the flat-tappet on his 575 upgrade. I just don't understand why I need roller cams in my application.

Kurt

We are in the process of rebuilding a 575 that wiped out two lobes on stock cam. I like the hydraulic rollers, so far 0 failures with comp lifters.

Kurt,
Two of the factors determining the necessity for roller lifters are camshaft intensity (the lower the number the more aggressive the ramp) and lift. By comparing two Crane blower grinds of similar adv duration, one hyd flat, the other hyd roller, you can illustrate the point.

CRA 134561 Hyd flat
Adv...... .050........ lift
296/306 236/246 .553/.571
Lobe intensity 60/60

CRA 138781 Hyd roller
Adv.... .050 ........ lift
296/304 246/254 .615/.636
Lobe intensity 50/50

The roller grind has a significantly more aggressive ramp as compared to the flat and has .062/.065 more lift. The need for the change from flat to roller is dependent on the aggressiveness of the grind you choose. Hope this helps clarify the question.
Bob