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Camshaft wear and other ramblings

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zottlander

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Pulled the engine(had 140,140,160,142 compression) Turns out the cam was having a lifter or two for lunch. I had a kent cam with .381 or .377 lift. the guy over at TNN that wrote the great ref. stuff says .29 and above wears the guides. My machine shop guy says that .381 is a lot of lift for a baby engine. I noticed on Paul's site that TT has the most conservative cams. I think the biggest in that column was .302(for race) I will use a less agressive cam in the rebuild. The previous owner had the block line bored for cam bearings so those will be also replaced. I wonder if the dual springs also cause some lifter wear? The lifters were battered, one was concave, a couple had pitting. I am
putting in pilot lifters and thinking about nitriding the cam shaft. Do you guys have any opinions on nitriding rings? thanks....
 
zottlander, Isky makes a great set of double valve springs. I have put them on high lift cams and stock engines with no problems and a lot of these guys and gals were doing some serious autocrossing. Isky sells a lot of light weight valve train parts. Just my experience on this and I'm sure there is a bunch of good stuff out there. Wayne
 
Zott, the last full race 1500 I built only had .320" lift at the lobe, .528" at the valve. If you were running .380 at the lobe, I'm surprised the engine ran below about 3000 RPM. As long as your valve geometry is correct, higher lift should put very little strain on the guides. I had roller rockers on mine, and ran the thing for four full race seasons, and it still has the guides in it that I installed in 2000.
There are some really crappy lifters out there, so be careful. I had one that was soft, and it ate the lobe off the cam quick as a bunny. Like, RIGHT NOW! The face of the lifter should be no softer than 51, Rockwell "C".
I sent all the lifters I had out and had them checked, hardened and reground. Never a problem since. I had one lifter showing some minor pitting at the last rebuild, this past July, but that could have been caused by the engine spinning a rod bearing. No cam damage at all.
What cam bearings do you use after opening up the bores for bearings? I'm curious, as I just run the small journal cam, and install early 1300, or TR6 bearings in the block. Make sure the cam and lifters are getting LOTS of oil, as oil starvation will cause nearly immediate problems. Assembly lube, and proper cam break-in procedures are crucial, as well.
I've never heard of nitriding rings, and think it would probably make them pretty brittle. I always nitride the cam and crank, though.
Jeff
 
It sounds from Jeff's reply as though you have a Spitfire 1500, in which case that is a huge amount of lift. (Bigger engines will be "milder" with any given lift and duration than an engine of smaller capacity.
Its a combination of the cam profile and the greater pressure from the stronger valve springs that are needed that causes accelerated wear, but as Jeff says if the lifters are correctly hardened they should last a long time.
In my TR4a I have a cam sold by Triumphtune as a "Sprint 88", which is made by Kent and I have used this with the lightweight lifters for 4 years, no problems.
Good luck, Simon.
 
Just as an informational point, and probably beyond this discussion, but sharp cam ramp angles and excessive valve spring pressures can cause the head of a valve to snap off. At which time, your engine makes the sound of a very expensive boat anchor.
BT,DT
Jeff
 
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