if you've been through two flat tappet 455s in short mileage, you need to figure out why. Properly broken in and run on oil with sufficient zinc compounds, they ought to run about six forevers. If your rebuilder is using lifters from India and cams from the heathen chinee, all bets are off. If the failed engine were built with OEM or better components, I'd go find out why they died. Roller lifters do in fact reduce fristion substantially, a concern more at stratospheric RPMs than the speeds these coaches turn them. The gurus maintain that the flat tappet engines want oil with fairly high zinc concentration, they're available and have been much discussed here.

--johnny

How about a NEW manny diesel???

Karen,
Roller lifters are good for avoiding this problem.
In California, be very careful as to what profile to use as you can find
that it gets very difficult to pass the BAR smog test.
I'm always nervous as a prostitute in church when we break in a rebuilt
engine.
We have put several roller cams with good results. The roller will allow
the valves to open at at faster rate and close at the same degree.
Dick P. does not recommend rollers, but I tend to favor it assuming your
aware of what set up to use, otherwise it becomes problem selecting simple
things as valve covers.
I have assisted many on the phone to have a carefree roller set up.

Karen,

A photo is worth a thousand words so:

http://www.gmcmhphotos.com/photos/modified-roller-tappets/p60079-modifed-lifters-a.html

Regards,
Rob M.
The Pedantic Mechanic

Karen is one sharp person, once she sees the roller tappets she will
immediately see and know why we need to grind the upper portion of the
extra long lifter.
She understands mechanical better than most men , but very beautiful Lady
as well.
I always run out of my office to see and flirt with her too.