I hear you. My pistons were to be 2 weeks, took 6. Cams are now at 3.5 months and still going strong......
Mr Fordboy, while you are hanging about here, I know you have more experience with pushrod type engines than DOHC stuff with direct tappets or followers but do you have thoughts about breaking in new cams in this setting (direct tappets in this case),. I know regular flat tappet cams take a lot of babying in many situations to avoid wiping the lobes but with DOHC direct, the tappets don't rotate, are flat, but the actual load is much less. Less spring pressure, no rocker arm to multiply load on the lifter etc. Other than assembly lube in general would you do anything special lube/oil wise as is often suggested with pushrod flat tappets? Though way down the road for you and Midget, it does apply.....
Jack,
As a matter of fact, back in the 80's and early 90's when I founded and owned PHP Racengines, I seem to remember building & dyno'ing about 100 Lotus TwinCams & Cosworth BD & FV variants, all with bucket "flat" tappets. There can be problems with these types of valve trains.
My thoughts:
1] Chilled iron cams with steel tappets have better "compatibility" than steel cams with steel tappets.
2] Contact pressure is also a factor for break-in, I insist on running in on lowered valve spring pressure, NO MATTER HOW MUCH TROUBLE IT IS TO CHANGE VALVE SPRINGS.
It is worth the effort. I usually remove the inner spring, minimum, for "break-in". Break-in rpm needs to be carefully controlled at reduced spring pressures.
3] If the tappet is dead flat, I request the cam lobes be ground with "extra" lobe taper and/or offset, to spin the lifter. NO tappet will survive without rotation.
4] If the cam grinder recommends against a "flat" tappet, inquire as to whether they can spherically grind the tappet to a radius they recommend for "their" lobe taper. If
not, Dema Elgin can spherically grind tappets to a variety of radii. One might inquire whether he has a setup for the tappet diameter you are using if you need this done.
5] I had steel cams nitrided after grinding.
6] "Parkerizing" of steel cams lobes and steel tappet surfaces is also a good idea that helps lubrication. Chilled cast iron cams may not need this process. DLC coatings
are now being used to help with some of this, but I do not have any experience with them in this application. Compatibility is a huge factor with DLC. And it is
expensive.
7] My experience is that the tappets need to be about 54/58 Rc hardness. Harder is not a problem on the tappet, I've used parts as hard as 65 Rc.
8] Cams need to be 4/5 Rc hardness points softer than the tappet. Cams/tappets at the same hardness are usually a problem.
9] Rc hardness is relative, and can be less if the cam lobe nose "contact pressure" is less or low. Good cam grinders can advise a user on this. HIGH contact pressures,
as in high velocity/acceleration cam lobes, with high valve spring pressures, and high valve train mass, need "harder" parts, and even this might not prevent wear.
10] I always insist on a cam break-in lube with "moly", generously applied during assembly. Don't go nuts, but thoroughly coat both the lobes & tappets.
11] I always add a ZDDP additive on top of the moly assembly lubed lobes & tappets. I tend to drown the parts. This is only for flat tappet cams.
12] I like regular racing oil for "break-in" as opposed to break-in oils. I worry about bearings too. I tend to use lighter weight, multi-grade oils. There is so much new
information out there, or on the web, I would advise being careful with oil choice. I tend to go for oils with higher film strength, because I am an advocate of "lower" oil
pressure in general.
All of this will apply to the new engine for the Milwaukee Midget. It is going to be interesting . . . . . .
Fordboy