Re: Camshaft worn?
Posted: Sat Jul 07, 2012 4:46 pm
The cam probably wasn't processed properly after grinding. I have had numerous re ground cams over the years without problems. Cam failure is really quite rare. I find it hard to believe that a reputable cam grinder would send out an unprocessed cam. What followers did you use after installing the old cam?
If you use the correct cam lube (copious application to the cam and follwers, including the follower bores, is customary), the setting of the cam timing should not cause any problems. Note that if that little bit of rubbing when turning the engine by hand did cause a problem, the cam doesn't have a chance in hell of lasting more than a few miles. I always use a good assembly lube as well. The lube wont rub off...
One thing that can cause problems with the cam wear you describe is improper valve train geometry. That all of the lobes were damaged might point to those valve springs again, and the rockers. If the cylinder head has been milled a little (say, you have combustion chambers at around 21 cc), you would need to shim the rocker towers or the springs will get close to packing up solid, and the pushrods may bend. I had to do this with my last Longman race head when I checked the clearances after cam timing and assembly. Valve float can be hard on the cam, lifters, rockers and pushrods as well. Make sure that you have the correct ratio rockers to match your new cam. Improper valve train geometry is not unusual with some cam combinations when used with a modified cylinder head. You may have to put a few thou shim under those towers to correct it.
Note that many roller rockers wont fit properly beneath an alloy rocker box cover without machining the internal ribs from the inside of the cover. Just another thing to look at. Stock steel boxes work fine with most roller rockers.
Make sure that you have full oil pressure prior to the first engine start. This often requires a couple of minutes of cranking to ensure that you have oil pressure. I pull the oil pressure sending line to see the oil coming out, and to eliminate any bubbles in the line. I do the start once I have a solid oil pressure indication at the gauge during cranking. If you can pre lube to bring up the pressure prior to cranking, all the better. Anyway, this will ensure that the cam is bathed in oil as well as cam lube.
Most cam grinders recommend 20 minutes of running at 2000 RPM for cam break in. I suggest that you break in on conventional race oil, with a ZDDP break in additive. If the engine heats up, stop the break in, let it cool, then continue when it is safe.
That said, I have started a few engines, and just took them for a drive. This resulted in a good break in of the cam, without problems. I did this with my current 1380/scatter pattern regrind cam engine, which now has 18,000 miles. I still recommend the 20 minute, 2000 RPM break in.
I have not had to adjust the valves in more than 12,000 miles.
You might also check to ensure that you have proper cam lubrication, and that all the oil passages in the block are clear. Your block should have threaded plugs to make blowing out the passages easier. Check the cam bearings and make sure that there is clear passage for the oil.
If you use the correct cam lube (copious application to the cam and follwers, including the follower bores, is customary), the setting of the cam timing should not cause any problems. Note that if that little bit of rubbing when turning the engine by hand did cause a problem, the cam doesn't have a chance in hell of lasting more than a few miles. I always use a good assembly lube as well. The lube wont rub off...
One thing that can cause problems with the cam wear you describe is improper valve train geometry. That all of the lobes were damaged might point to those valve springs again, and the rockers. If the cylinder head has been milled a little (say, you have combustion chambers at around 21 cc), you would need to shim the rocker towers or the springs will get close to packing up solid, and the pushrods may bend. I had to do this with my last Longman race head when I checked the clearances after cam timing and assembly. Valve float can be hard on the cam, lifters, rockers and pushrods as well. Make sure that you have the correct ratio rockers to match your new cam. Improper valve train geometry is not unusual with some cam combinations when used with a modified cylinder head. You may have to put a few thou shim under those towers to correct it.
Note that many roller rockers wont fit properly beneath an alloy rocker box cover without machining the internal ribs from the inside of the cover. Just another thing to look at. Stock steel boxes work fine with most roller rockers.
Make sure that you have full oil pressure prior to the first engine start. This often requires a couple of minutes of cranking to ensure that you have oil pressure. I pull the oil pressure sending line to see the oil coming out, and to eliminate any bubbles in the line. I do the start once I have a solid oil pressure indication at the gauge during cranking. If you can pre lube to bring up the pressure prior to cranking, all the better. Anyway, this will ensure that the cam is bathed in oil as well as cam lube.
Most cam grinders recommend 20 minutes of running at 2000 RPM for cam break in. I suggest that you break in on conventional race oil, with a ZDDP break in additive. If the engine heats up, stop the break in, let it cool, then continue when it is safe.
That said, I have started a few engines, and just took them for a drive. This resulted in a good break in of the cam, without problems. I did this with my current 1380/scatter pattern regrind cam engine, which now has 18,000 miles. I still recommend the 20 minute, 2000 RPM break in.
I have not had to adjust the valves in more than 12,000 miles.
You might also check to ensure that you have proper cam lubrication, and that all the oil passages in the block are clear. Your block should have threaded plugs to make blowing out the passages easier. Check the cam bearings and make sure that there is clear passage for the oil.