So it finally warmed up a few degrees and I went out to start my old convertible that has been parked since September. It started straight up, being a fresh rebuild, but it still hammered. So here's what happened; - the car broke a rocker-shaft on a long trip last September, and I've since replaced it. The motor still ticks though, and the vacuum profile sucks. I assumed that I damaged the #6 or #8 exhaust valves, considering that these cylinders were both shut down for about 300 miles once the rocker shaft broke. Today I pulled off the cover, and found that the number 4 cylinder exhaust valve (rocker set-up) had slack in it, meaning that there's either a bad lifter or possibly the cam's gone. The others were all fine, and under "load". The valve seems to seal and the height looks correct, so it's not a bent or shot guide, or a broken spring. Compression on that cylinder is still good. The funny thing is that once I inserted a screwdriver blade and closed the distance between the valve and the rocker arm, the car quieted right down, and ran better. The clearance is there when the engine is running or not. The rocker arm is not bent, or disfigured or worn in any way. Does this imply that the cam is gone, or is the lifter gone? Both were new in August. The pushrod looked okay, and was straight. I couldn't "feel" any sinking in the lifter when I pushed on it. A couple of questions; - is it possible to check a cam for worn lobes while still in the block, or would it be better if I removed it? How would one go about doing a check? How high are the lobes supposed to be? Next question; - I'm seeing that there's an outfit selling Isky cams for nailheads, are these good cams? Would it last longer than the generic one I've got? - assuming of course, that I have to replace this one...
Sure. Figure out what the lift is supposed to be, then measure what it actually is. Lobe lift would be better than valve lift--but it's only mathematics; it'll be easy enough to convert from one to the other. Naw, too much work. Find out if there's a problem before ripping the engine apart. If the lifter is bad, the cam will be bad. If the cam is bad, the lifter will be bad. That info will be on your cam card; or call the company that made the cam and ask 'em.
Pull the intake manifold and remove the center valley cover,,,, then ck out the lifter,,,, and the cam lobe.... if the cam lobe is wiped out, you will be able to see it right off.... if the cam lobe is ok then replace the lifter and put it back together.... lube the new lifter foot with moly grease as you put it in... it is normal for a used cam with a lot of miles to have some little pits in it as long as they are not severe.... if the nose of the cam lobe is still good and sharp and not rounded like a silver dollar... If the cam lobe is wiped out the oil pump will be damaged and all the bottom end bearings will have metal chips in them....the oil filter will not keep this from happening.... because on start up especially when cold the filter goes into by pass mode and lets the chips thru.... Usually the cause of a broken rocker arm shaft is that the shaft was not properly tightened down..... you have to start in the middle and work out toward both ends and then torque the bolts the same way... and after warm up recheck the torque from the centers out to each end... of course when doing this keep the tightening as even as possible....that is to say dont tighten the center bolts all the way down first and then move to the ends.... starting in the center take them down say 5 turns each and then move back to the center and start over again....untill they all come up snug and then from the center torque them down....
Yup...Follow Doc's prescription,,,pull intake and valley cover to do a visual inspection. The Isky cams I've seen lately are near stock grinds, some are even milder! Factory 401-425 cams had about 207 to 209 degrees duration at 0.050" lifter rise. Lift is around 0.440" at the valve, stock. Poston, TA Performance, Comp, and Carmen Faso have new cams available.
could always check the length of the offending pushrod against the other "good" ones.. who knows, could be some flukeo No:
Doc, please explain how metal could skip both filters and end up in the bearings. What is the likelihood of both bypass valves being open?
Even if the cam looks good, check to make sure the lifter is ok. Sometimes lifters can get worn and have a concave (pushed in) face where they ride on the cam. I tore down a 401 core motor that had a bunch of worn lifters like this-high mileage, low maintenance for sure. Doc is right, your oil can by-pass the filter, especially if the filter is already dirty/clogged internally. Or cold temps and thick oil can raise the resistance/internal pressure high enough to allow the oil to bypass the filter. The screen on the oilpump really does not filter much other than busted pistons, left over missing bolts, nuts, washers etc... It can not filter out metal shavings/grindings etc... If it were to become clogged with such, it would starve the pump and inturn starve the bearings etc... from oil.
Yep, all it takes is a pressure differential of 12 lb. and the by pass spring will let oil go around the filter.... the factories figgured that this was better than letting the bearings starve if the filter cant handel it for some reason.... To answer your question, a cold start and reving the engine to keep it running will make the by pass kick in,,,, winging the throttle ,,,, clogging,,,, ect..... Both filters????? all my engines only have one.... I do use ''full flow '' filters only because they are best.... cut some of them open sometime and see what is inside of the different brands,,,, a real eye opener.....
Thanks for all the advice so far, - I'm beginning to think it may just be a busted lifter or a short (for whatever reason) pushrod. The valve actually functioned like it was supposed to when a screwdriver blade was placed between it and the rocker arm, - full valve stroke. What scares me the most on this car is the fact that this is a new rebuild, the engine doesn't even have 3000 miles on it yet, and already it seems that the lifters or the cam are failing. I was careful with the oil changes, it has ZDDP in it right now, and had it right from the first start. The temperature around here plunged back down into the -20's yesterday, and it looks like it'll be a while before I can get back out there and pull that manifold off. I thought the pushrods were all the same size; - funny; I can't remember putting them all together though, I just inspected them and checked for straightness when I pulled that broken rocker shaft off. I'll let you know when I find out.
Come on Marc -20 taint nothin. You've had good advice. The nail intake is 'dry' = no coolant and not many bolts-it's the weekend-go for it-good luck
The pushrods should be different lengths for 322-364- and 401-425s.... but for each engine they should all be the same length.... I built an engine a short while back and it trashed the cam..... I have access to a rock well hardness testor.... the lifter that trashed the cam rockwelled to the same hardness as mild steel.... need I say more????? lasted about 1500 miles before it went to making noise.... you pay good money for parts and they give you stuff that is not properly heat treated.....
Lemme guess, Doc, more foreign-made crap with a generic label; - seems there's a lot of that going around. I really hope that this hasn't shot-gunned my cam as well, but you're probably right, it's probably junk by now too. I'm going to start looking for stuff that says "Made in USA" and pay the extra money for it if necessary. This is the 3rd engine kit that I've bought that would have sub-standard parts in it. It's enough to drive one to drink... -25 plus is bad enough, thanks, even though it's only eight bolts and a set of cover bolts. Try and fiddle the stator switch and carb clips without losing them. Frozen fingers tend not to work very well and drop things. It's guarranteed that I'd wind up with a couple of busted electrical clips at that temperature. Gaskets have this nasty tendency to break, grease doesn't stick, or any kind of goop (sylicon) won't set up. Besides, I gooped that manifold up so well (badly) that I'm going to have to have a crowbar and a vacuum on standby when I take it off, it's going to be a mess. I'll wait until it's warmer...besides, have any of you ever pulled a starter in a parking lot when it's -40? I have, and my fingers have never forgotten it. Next year will be better, we're going to have the shop heated by then.
I understand,,,, that is the only thing that I dont like about tenn...... the cold in the winter..... I was raised up down on the gulf coast..... I have used heat lamps , electric heaters, propane heaters, ect..... but best is sitting by my wood stove with a hot cup of coffee..... i dont know what brands you have available to you there but the lifters that went bad for me was engine tech brand.... rest assured that the next set of lifters I put in the engine was melling.... and the cam was melling.... made in the usa..... on this latest engine that I built, i used a posten nh400 cam and thier lifters.... with moly grease,,, not liquid,,,, dont use the liquid cam lubes because it drains off the parts.... use grease,,,, I use arp moly grease, it stays on the parts.... I also put the zzdp zinc additive in the start up oil..... fired up reved up to a good brisk idle and let the engine warm up all the way....till the rad burped,,,, got the timing set,,,,, ran it for about 30 minutes.... and then shut it down and celebrated because that was the first time the thing had run in 5 years.....
