I think I am starting to have the same issue with my 68 GS 400 I had when I got it. The camshaft had worn #1 lobe so I had it replaced. Everything looked okay, I had the oil pump redone, used the booster plate, it has run fine for about 900 miles. This week I notice the oil light staying on a little longer than I like and now there is a noise like what I heard when the camshaft went out. Knowing it was rebuilt by a shop that was not a Buick familier place I just assumed they got a bad camshaft or break in was not done properly. Now I am starting to think I have an issue somewhere in the motor and I am looking for ideas. The engine build is as follows; Bottom end was rebuilt to factory specs, and inspection when I had the last problem did not turn up any visual issues, nor was there any noises after the cam was installed. Edelbrock heads installed, I am assuming they replaced the cam bearings, it has a T/A cam that is not to radical as it is an A/C car, it has some kind of fancy rods (4340?) and the whole assembly was balanced, it has the standard oiling system using the old style pickup. I am starting to think perhaps I have a cam bearing problem? This is venture that I have not taken in way too many years, so I am looking for some feedback as to things I should have checked if indeed I need to have another cam put in. Any ideas will be appreciated, I do not think the bottom end is having any issues as my shop took a look at that the last time. It is like the oil pump loses its prime, and I am now getting a knocking sound when I start it, this was the same thing that happened last time. The front cover did not appear to have any issue with scoring last time we had it off. I am not too sure where to look for answers, anybody have any ideas? George getoth@gmail.com
If you suspect cam lobes, the way to check is to remove the valve covers and watch rocker motion while cranking (disconnect the coil wire). If you don't see a rocker or rockers showing a significant lack of regular motion, the next step is to pull the rocker shafts and pit a dial indicator on the tip of each pushrod and measure lobe lift. The exhaust lobes should all have very similar lift, the same for intakes. Since the last rebuild, have you been using motor oil with a significant amount of ZDDP? Most off the shelf oils are inadequate for flat tappet cams and require a zddp booster. In the end though, a flat lobe or lobes shouldn't affect oil pressure. You should install a gauge that reads in PSI to really know what's going on with pressure. Devon
What brand of oil filter are you using? Some non-AC Delco filters do not have an anti-drainback valve and all your oil filter and oil passages have drained out, causing a dry start and extended time to refill the filter and passages. I never used one but I was always told never use a Fram filter and I never have.
Only use A C oil filters, and yes I am using a ZDDP additive. I am going to have a compression check and if the #1 cyclinder is very low I will have to assume the cam lobe is wiped again. At that point though, what would cause the cam to wipe a lobe? Obviously low ol pressure, but the bottom end does not seem to have issues. So what would cause low pressure at the cam, but yet supply enough to allow the bottom end to be okay? What would be a cause of low pressure at the cam but not destroy the bottom end? Not having rebuilt these motors I am at a loss.
For clarification, the camshaft lobes are not lubed by direct pressure, but rather splash from the reciprocating assembly and whatever falls off the lifter valley. You can have low oil pressure and still have healthy cam lubrication. At this point, we don't know if the bottom end is OK and we don't know if the camshaft is OK. Put an oil pressure gauge on it and let us know what you see. Devon
George, My new engine made the same knocking sound on startup - even when warm after sitting just 20 minutes. I have a new TA timing cover with their adjustable regulator. I just cranked the regulator in a couple of turns and I no longer have the knocking. That is what I suggest to you. The adjustable regulator is relatively inexpensive.
when the cam lobe was wiped out, wonder if all the metal off the cam lobe did some damage getting all over in the engine.
