I swear, I have never seen an engine so hell bent on self-destruction in my life! For your reading pleasure, (It's long) take your pick between any of these problems… (For those not familiar with my previous post, Loose Wrist Pin, this a Pontiac 400 engine.)
One common denominator I am seeing in this tear down is the excessive wear, (IMO) possibly due to a lack of lubrication. This engine has about 1,000 miles since the second rebuild. Oil pressure is 20PSI hot at idle and close to 60PSI hot at 2,000 RPM.
#1. I can feel a ridge on the cylinders! The walls are already polished with only an occasional hint of the original crosshatch visible. They are KB hypereutectic pistons with moly rings and .003” clearance, according to the machine shop. He says that’s a “perfect” clearance. KB recommends .002” - .0025”. For supercharged, racing, nitro, etc., clearances can be up around .004” - .005”. So I guess .003” is OK, maybe a little noisy. I assume the higher heat in race engines expands the pistons more than a street engine. I don’t have the necessary tools to measure them myself.
#2. The rod and main bearings again seem to have more wear than normal. When I tore down the engine after it over heated, it had about 7,000 miles on it and the rod bearings were worn to the point of some of them were showing copper on the rod side. That was my bad for not investigating this more. Based on my Plastigage measurements, (I know), rod clearances and main clearances have increased by .0005 - .001”. Apparently, these clearances don’t affect the oil pressure. The oil pump had no wear to speak of. I couldn’t find clearance specifications anywhere.
I found that Melling doesn’t offer a high volume pump, just a high pressure. Since this pump can keep up the volume with these clearances I figure a high pressure one will definitely increase the pressure. BTW, I wonder if the oil gauge I used could be erroneous? I might do a bench test and run the pump up to its bypass pressure and compare different gauges.
#3. On the first rebuild two lifters had a narrow groove on their faces, which seemed to indicate that they were not rotating. I changed the cam and lifters. When I was troubleshooting this knock, some of them didn’t appear to be rotating. A rep at Comp Cams seemed to think it was an oiling issue. Upon teardown, no grooves were found. Funny looking wear patterns though. Using the side of another lifter as a straight edge, a random sample shows them to still have a crown.
I also tested them by installing the cam and a lifter with a pushrod and rotating the cam with my drill and putting hand pressure on the pushrods and they all rotated somewhat. Don’t know how scientific that is or what that proves… The cam lobes all have the same wear pattern too. Again, not what I would expect for a low mileage cam. I’m used to seeing wear across the nose of the lobes and then it narrows down as it travels toward the base.
#4 Finally, I have ½” slop in the timing chain. Too much? It’s a stock style, non-roller chain.
Fresh bore on cylinders? I cannot comment on KB pistons as I have not used them, but I have read/heard not so good things about them New rod bolts? Plastigage is a great tool, been around a long time, but I still only use it as a 2nd check upon assembly. i torque caps together with bearings and check with an inside micrometer. I just finished a 400 build with a melling HV pump from Butler Perf. All my mains were .002-.0028 rods .0015 my oil PSi read 25psi in gear hot 60 when driving, which is acceptable to me.
Yes, fresh .060" bore. I always thought KB was a top brand piston. I assume new rod bolts as they were supposed to be reconditioned.
I never found a high volume pump from Melling, just standard and high pressure models.
I came up with another theory: #1. With the gouges in the cylinder, I figure the engine should have been pumping oil like crazy. All I ever saw was slight smoking usually at fast idle.
#2 That suggests there isn't much oil being splashed on the cylinder walls.
So, how can I have apparently good oil pressure yet very little oil being slung off the crank? I'm thinking a restriction somewhere between immediately before the first bearing and the pump. That would give normal oil pressure yet no flow to the rest of the engine.
I'm grasping at straws now but I have to start somewhere! I'll be looking at the block to test this.
I'm also thinking of mocking up the block without the oil pan and run the pump with a 1/2" drill to see what kind of oiling action there is. I did this before on a SBC with low RPM oil pressure problems and found a leak between the rear cap and pump.
I'm no expert engine builder but I've done my share.
Lately I've found one has to remeasure and recheck everything the machine shop does. The trend seems to be more clearance in the mains. The guy who machined mine bored the mainline for 3.5 thou., even though I told him I wanted stock clearances and I'm building a street car not a race car. He's a Ford guy and builds drag race engines. He had to re-do the mains and in the process ground the caps at an angle other than 90 deg. That was reason for yet another mainline bore. I found three other vital mistakes after I did all my pre-assembly inspections. Obviously I have another machinist. Sorry to get off topic.
Some debris may have been in your oil. If the block and all the components are not thoroughly cleaned any dirt will cause wear. Of course the worn off metal will accelerate more wear. The whole works should be washed with soap and water before it is assembled even if the machine shop says it's clean and ready to go.
The journals on that camshaft appear to be a little beat-up. Old engine blocks can settle and slightly change shape with 40 years of use and countless cycles of heating and cooling. Pontiac blocks have been known to settle enough to have a cam tunnel not quite true. Be sure to check the cam tunnel for straightness and roundness. I measured all my cam bores, they were round, but when I installed the camshaft it would not turn freely, The tunnel was not true.
Your pistons may have had the correct clearances but what about the rings? Not only gap but ring side clearance and depth as well. If the rings are too tight in the cylinder it could cause wear.
Did you check lifter to bore clearance?
As far as oil pressure and clearance, some say to increase the main clearance to get a larger oil wedge between the bearing and journal and more oil flow between the bearings and journals may lower oil and operating temps. I think a standard Melling pump and a 2-1/2 thou. clearance will give you enough oil and still have preasure at the red light on 95 degree weather.
Sorry again, I'm running off at the mouth.
If your pin is loose in the rod and came in contact with the cylinder wall it could have been the root to all your problems.
Some of the lubrication for the cylinder walls and camshaft comes from oil dripper holes at the mating surfaces of the rod and cap. I don't have a set in front of me but can these holes be machined away when re-sizeing the rods?
Thanks Bluebird. You must be single. That sure is a pretty kitchen to be washing pistons!
I do my best to verify clearances from the machine shop. I have a dial caliper and dial indicator and have to use Plastigage, but it's better than nothing.
I use dish washing detergent, brushes and a pressure wash on my engines. I was surprised to see those scratches.
On the first rebuild I had a cam that would bind on every rotation. I think the runout was like .006". The replacement cam and the Comp Cam I installed on the last build turned free and true. Same with the crank. I guess I could have measured the runout on both but the fact that they turned freely made me feel confident they were true.
Ring gaps were on the wide end of specs, but I didn't check side clearance or depth. I know the rings didn't stick out from the ring lands.
Didn't check lifter clearance. Are you suggesting they might be too wide?
I feel the loose pin is a separate problem from my wear. I had worn bearings after the first rebuild but I contributed that to detonation with the factory 10.75 CR. The machine shop seemed to agree with me. And, two lifters were worn because of not turning. I figured I didn't do a good job of breaking it in. I also use ZDDP. The pump seemed to check out. I couldn't find clearance specs on it, but there was no wear that I would consider excessive.
I feel I blew it on the second rebuild because I didn't take enough action to address the wear from the first rebuild.
Ain't gonna happen this time! Got to find something.
My restriction theory is all I have now. I briefly checked the oil galleys last night but nothing hit me in the face.
I have discovered that for several years all replacement bearings do not have the corresponding holes to allow oil to squirt out of the rod holes. I guess research proved it was unnecessary.
My holes are still there after the recondition, pointing at the cam, but rendered useless by the bearings.
No they don't use the holes anymore, my rods don't have the holes either.
Just wondering if the lifters could be binding in the bores.
My cam had a run-out of one thou. but still wouldn't turn freely in the bearings, I had to bore the cam tunnel.
If there is no physical evidence of a problem with the piston/rings and cylinders I suppose lack of oil could be the reason the cylinder walls have the cross-hatching worn off. Or metal in the oil acting as an abrasive on the rings, the journals and the lobes.
Yes I'm single but living in sin. When my buddy saw the pistons on the sink drain and realized Karen let me wash them in the kitchen sink he said "you better marry that girl". Wedding is set for September.
Do mean the condition of the top end? I haven't checked the heads. All new valves, springs, etc. Since they have just 7,000 miles on them, they have been low on the priority list as far as inspecting them.
On the metal comment, there was a thin layer of sludge-like material on the bottom of the pan. Just for grins I stuck a magnet in it but it didn't seem to attract anything. I wonder if I could get an oil analysis around here...
Yeah, any sign of lack of lubrication up there? Rocker cups rocker shafts or balls whatever style you have on, scratched valve stems, wear on the push rod tips?
I feel for you, these are some sad pics of the cylinder and piston, and like you I have mine out for the third time although for a rear seal problem. I have a set of rods out of my 428 you can have if that will help although the cost of getting them there and getting them checked out my not be much cheaper than a set of aftermarket, offer is there if you want.
I'll check up there for wear too. Today will be the first full day I can devote to this dilemma.
I believe the machine shop has found a set of rods and even a block. But, I think we're going to go with a sleeve because it's numbers matching.
The only thing I'm worried about is the ridge on the other cylinders. If they are worn too much, I'm screwed. Sleeves on all 8 would be too much to handle at this time.
Maybe a new block will be in order and just keep the old one for future repairs when it can be afforded.
I'd put that one away and use a different motor. Save that one for the next owner to work on. Better yet just buy a used motor off CL to drive around and put that one in the corner. Probably have less money in it than rebuilding this one.
I'd put that one away and use a different motor. Save that one for the next owner to work on. Better yet just buy a used motor off CL to drive around and put that one in the corner. Probably have less money in it than rebuilding this one.
The more I think about it, I agree. Especially if all cylinders need sleeved. I may be lucky to get it bored to .065. Man that is getting thin. I would need to have it sonic checked.
I have been down this same road on my friend 67 engine with the KB pistons. Long story short the machine shop did not read the instructions that came with the pistons. There was 1/2" of metal at the bottom of the oil pan from the cylinders that looked like a 300,000 mile engine. But this engine had 100 miles the most.
All lubricated parts were installed: crank, rods, cam, lifters. All plugs installed. Oil filter installed with oil pressure gauge installed at filter adapter. Oil pump screen removed and hose inserted into inlet hole. With no rings installed, the crank turned over very easily by hand using the front snout. Same with the cam. No binding.
Inserted prelube tool. Drill is rated at 600 RPM so with a load I estimated 400-500 RPM. That translates to 800-1000 engine RPM.
Old oil change oil was used. Oil pressure was 55 PSI at full speed on drill. Even at a crawl, maybe 400 engine RPM?, I got 20 PSI. That would be expected with old and cold oil.
Oil is draining everywhere from the bearings of the crank mains, rods, cam, and also from the lifter pushrod cups. It took just a few seconds for the lifters to start oozing.
A few observations:
The front two plugs were leaking. I didn’t seal them so that’s probably why. I was hoping that was the problem until I rotated the cam and got squirted with oil coming out from behind the retaining plate. It squirts once every rotation I guess to oil the timing set. With that kind of leak the plug seepage is negligible.
I tried monitoring oil pressure from the port by the distributor. Same pressure. I was looking for a difference before and after the filter.
For an experiment, I removed the galley plug first in line with the flow, driver’s) oil pressure was zero. (A pump without a restriction can really pump!) I reinstalled that plug and removed the other, (last in line) and the pressure made it to 20 PSI.
I realized that there is apparently nothing wrong with the oil flow. So I started to theorize that the Fram filter, that I have learned a lot of people don’t recommend, may have had its element blow open, allowing dirty oil to continuously recirculate. I cut it open and it looked OK to me. (Of course the first filter could have blown. It's long gone.) I also checked the filter housing/adapter oil bypass. The fiber disc had a nice ring pattern from its seat. The spring was intact and holding the disc to the seat. Looks just like it did the first time I assembled the engine.
Another observation that still nags me is the fact the gouges in the cylinder should have made the engine smoke like crazy IMO. There seems to be enough oil drainage that would splash enough oil on the walls to get oil up into the combustion chamber. But, since I have nothing to compare it to, I don’t know if it should flow more.
So, I’m back to square one. I can’t see anything obviously wrong.
So, I’m gonna wait for the machine shop to call back to see what else he has come up with as far as replacement parts. Using a different block that he found is looking better all the time. I’m also going to see how much he would charge to assemble the block. I’m gun shy now. It’s time step back. I just can’t justify me assembling it again without finding something out of line. If it wasn’t the fact that I can’t really tell if the motor is wearing excessively without tearing it down again, I might attempt it. But to drive it for who knows how many thousands of miles and visualize the motor eating itself would drive me crazy.
It looks to me like you have a couple of different things that went awry with this one. The pin walked out of the rod because it didn't have the right pressed fit when the pistons were installed. The KBs were probably not installed perfectly(apparently they need to be installed per detailed instructions to live, not something a normal shop is going to do unless they have dealt with it before). And the cam and lifters didn't break-in properly and therefore were going south in very short order(some don't even make it thru the break-in process these days). Simply speaking it's pretty much a total loss. I'd start all over again with new parts from different suppliers and never look back and not try to reuse any of the old internals. I'd even have the heads pulled apart and checked and cleaned before I'd try to put them back into service again.
I know nothing about KB pistons but the pins are pressed into the rods not the pistons. The pistons should float on the pins or is there something I am missing? Wouldn't be the first time. Have the pistons a history of the pin hole not being bored at 90 deg. with the stroke or some other issue?
No Blue, You're right the pins are pressed into the rods but it happens when you install the pistons on the rods. It's one operation is what I meant. It just sounds like the rod wasn't sized right for the pin fit or else it became loose from some other action while running. The KB Hypers have gotten a bad reputation over the years because there is apparently very specific guidelines that must be adhered to for them to live long and prosper. Not like a regular deal where you can buy off the shelf pistons and rings and drop in and go like most of us have done all our lives. If not done exactly to the manufacturers specs mostly the trouble I've heard are the tops above the top ring blow out. I guess the ring groove is closer to the top of the piston than others. Other thing have happened as well but that is the one that I've heard the most about. People that have taken the time and done things correctly have no complaints.
You know, it's funny, except for the damage to the one piston because of the loose pin, the other 7 seem to be still in perfect condition, even with the oiling issues.
Yes, by all the discriptive diagnosis it seems like the pin was not in the rod with the correct interference fit and came loose. Everything else was a result of that flaw. But why?
The machine shop will sleeve the one cylinder and the rest can be saved with a light hone. I'm really antsy on the hone because of the increased clearance I will get. They're also changing out the rods and looking for a new crank.
We never did really figure what the wear was from, although they say the scratches in the bearings were from dirt. I washed that block and all passages with hot soap and water until it was squeaky clean. I just don't know.
I got Rocky Rotella's book but that didn't help a whole lot. Most of the Pontiac idiosyncrasies in the book I already learned from you guys.
One thing I am going to do is send an oil sample to Blackstone Labs for analysis after a 1,000 miles of so to see if there are any abnormal readings from wearing parts. That will at least give me a peace of mind down the road.
