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Here is a question for you sbc motorheads out there.
Its about the 350 I built for my Blazer. Starting around 2000 rpms, my motor starts pinging (especially under load from towing). At first, I thought it was a high compression/low octane problem but now I'm stumped. :confused:

The motor is a '96 4 bolt chevy block, .030 keith black pistons, low compression heads off of a '95 caprice (non LT1), just installed another cam, I don't remember lift/duration but its just a notch or two above stock (mid 400 lift range) performer intake, Holley 600 carb. If it makes a difference it's in my '85 fullsize Blazer with a TH350, 4.56 gears and 38.5" tires.
I always run 93 octane, run the timing from backfiring all the way to detonation, oil pressure stays a steady 60 pounds (autometer gauges). The day before I drove her from Florida to Michigan, it sounded like I dropped a lifter (chattering like hell). upon inspection, I saw nothing out of the ordinary, but threw a new cam at it just for peace of mind, that's a 1200 mile trip! I've even tried straight 30 weight oil still the lifters seem to bleed down and cause the rockers to 'dance' after a few miles which would seem like enough time for the oil to heat up and lose viscosity in Florida heat. If I snug the rockers down to stop chattering, the nut will actually bottom out on the stud and still chatter.
Upon changing the cam, I didn't see any signs of heat or wear, it just seemed like the lifters didn't have enough pressure to remain pumped up.
The only thing I can think of is that I didn't replace the bypass (oil filter adapter) when I rebuilt the motor. This is driving me nuts! She made the cross country journey like a charm but I had to keep it under 50mph the whole way. Is it possible to lose internal psi to the cam but not drop on the pressure gauge? This problem has plagued me for the 20K+ mile life of this motor. Spark plugs have never shown any kind of detonation wear either.

Any help as to what I am overlooking is greatly appreciated. I'm not a greenhorn building small blocks, but this ones got me scratching my head!!!

I had that same problem with my 283. Thought it was bad gas. Finally retarded the spark just a little and the problem went away. Even got more low end power.

You said you played with the timing, did it get better or worse? The problem with the lifters may be push rod length. The 96 block came with a roller cam, I assume you still have a roller cam. It could be that you don't have the correct pushrods or lifters. If you can bottom the rocker out on the stud without loading the engine(lugging) you have something wrong. Are you getting any oil to the top end through the lifters. Keep in mind that roller blocks must use roller cams.

My mistake, the '96 block is in my S10 which is still using the factory roller cam. I can't get past the grime right now to see what year this one is, but it should be around the same year because it has the fuel pump boss plugged for fuel inj. This motor was installed by the PO and I remember thinking it was an Edelbrock crate at first because it was the newer style block, aluminum heads, intake, carb, elite valve covers, etc. But the cam was a small.350 lift Lunati fuel injection style hydraulic non roller cam. No rattle just underpowered.

I sunk the truck playing around in the mud one day and naturally, wiped all the bearings out of it. I had this block cleaned, bored, and the crank turned. Upon rebuild, I used newer heads with the factory rockers, pushrods that I had from other small blocks and a .454 lift hydraulic (non roller)cam.
For the longest time I thought the rattle was timing related because the rockers stay tight and flow oil freely from the pushrods when adjusting the valves w/the motor running. I have retarded the timing from the point of breaking the starter off the block all the way to pinging so bad that I thought the valves were gonna jump out of the heads with no change for the better. It is actually the valves floating. I know this is pretty longwinded but, maybe you can find where I went wrong.
At low rpms the valve train works like a charm, plenty of oil. I adjust them by loading each valve alittle, back off till chatter, then tighten 1/2 turn. If I make the valves chatter and shut it off, the lifters will have slack in them. If I tighten the rocker down to take up the slack and then restart the motor, it won't fire because then the valves are too tight. What would cause them to bleed down? :confused: Maybe I did use the wrong lenght pushrods? Would they still work at low rpms but float at high range. Thanks so much!

i don't see what kind of heads you're using.
later chebbies need self-aligning rockers....

It seems unlikely that all the lifters would bleed down. What ratio are your rocker arms? Factory rockers are 1.5, after market are available in 1.6 and 1.7 allowing the valves to open deeper into the combustion chamber. I would pull a push rod and measure it and then check it against your cam specs. You say that it has alluminum heads, has the block been decked. You may need to contact the manufacturer for advice. I would also talk to an enigine machine shop they should be able to shine some light on this.

If need be I can pull the valve covers and get the casting number, but for now they are newer centerbolt heads with self aligning rockers (I assume they are factory 1.5:1) I guess the only thing that would be suspect now would be the pushrods. I used to work for a Chevy dealer from '96 to 2000 and brought home many small blocks, heads, cranks & whatever I waranteed out. So most parts were early 90's & up. It's entirely possible that I used roller cam push rods with standard hydraulic but how do I find out?

Roller cam push rods are shorter than standard hydraulic push rods. Jeg's or Edelbrock should be able to give you the correct length. The shorter rods would account for the rocker being bottomed out.

Thanks, I'll check that tomarrow. I hope its just something stupid that I overlooked. Like I said, it's lasted over two years so far. Hopefully that's what it is.

I'll check the length and let ya know.

Thank you!

Shorter pushrods will definitely account for the rocker bottoming out. Look at it this way. If you have to run the nut down farther to get the rocker arm down to the end of the too-short pushrod, then you'll be partially opening the valves. This will result in severe loss of power due to lack of compression building in the cylinders. It will also result in the spring becoming over-compressed and experiencing coil-bind, which is probably the horrible clatter you're hearing.

Solution? Well, if you want to check this theory, go rent a compression tester and check the compression. If you're not building compression, it's a good sign that your valves are hanging open and not closing all the way.

If everything is stock and neither heads nor block have been shaved or decked, then measure the length of the pushrods you have and call Summit Racing (800-230-3030) and ask them what the length is on stock pushrods. If your rods are shorter, you might have just found your problem.

New pushrods are not that expensive. Just be careful to get the hardenned pushrods if you have guide plates in your heads. By trying to cut corners like this, you could end up destroying a much more expensive set of valve springs instead, or maybe even valves.

So before you run it one more time, I think you need to go after that compression test...or at least pull a pushrod and compare the measurements with a standard stock pushrod to make sure you at least have the right ones...since that is an unknown right now.

I've been driving it for two years that way, I even drove it for 32 hours straight when I moved up here. Just keep it under 2500rpm. That's what's funny, I'm running 38.5" tall tires and I can squak em and it'll put you back in the seat. There is plenty of compression, and power. The valves are opening and closing fully. Today I matched up a pushrod out of my wagon and it is the right length.
When started cold, all pushrods are snug against the lifters and rocker arm nuts are where they belong with only a few threads showing out of the top of the nut(no where near bottomed out).

While cold, I can push the motor over 5000 rpms with no noise. However,once the truck is driven for about 5-10 minutes and reaches operating temperature, the chatter starts. Eventhough the gauge shows no drop in pressure this is when the pushrods are loose when inspected.
Once this starts, the truck retains good power and sounds fine at rpms below about 2500. When I push it over 2500, you can hear the valves floating. Also the chattering sound comes from all over, not just one individual cylinder.
What's funny is the more I think about it this is starting to sound like weak valve springs?!?

I really appreciate all of the suggestions!
Thanks,
Scott

Yeah, that's what it sounds like to me.

I had dual valve springs in my '68 Firebird and it acted just like that. The bigger outer springs were broken, every one of them. And the inner springs were the only things keeping the valves from falling into the cylinders.

So check that. I'm glad you checked your pushrod length and eliminated that ugly possibility. Look really close at your springs and see if they're broken.

If they're not broken, then maybe they're fatigued...beyond their service life. You might try a new set of springs.

This still isn't making sense to me though, because if they WERE broken, it wouldn't rev when cold either. And if they're worn, I would think it'd be the same story.

...So I have to think about this.

I wonder if you're just detonating. That'll happen when it warms up but not when its cold, IF you're right on the ragged edge. Do you know what compression ratio it is? If you used really small chamber heads, you might have something like 12:1 compression.
An easy test would be to go get a gallon of really good race gas when you're almost on empty, and dump that in. If it runs great, then maybe all it is, is too high of compression.

Funny thing is, I stopped by my local machine shop this afternoon and ran my dilema past the guy there. He was scratching his head too.
This darn thing has symptoms of a number of problems, but I can't nail it down to one problem.
I don't remember off the top of my head what part # the pistons are, but I remember that the 58cc edelbrock heads that came on it originally were only like 10:1. These new heads are around 64cc and I run 93 religioulsy anyway. When this started the first thing I did was check the spark plugs. No signs of detonation whatsoever on plugs, pistons, or heads. This is when I noticed the slack in the pushrods.
Any experience I've had with busted valve springs has showed up as a dead cylinder throughout the entire rpm range, not just above a certain point.
This darn thing just seems to get better all the time.

Is there any chance you are sucking air somewhere in the oil pickup? This is what causes lifter tick in 235's- air gets into the oil pump and blows it into the lifters making them leak down. You might want to drop the pan and see how well the oil pickup is working.

You know, that is a good question. I have to pull the oil pan here soon to fix the small but annoying oil leak it has developed. I'll have to look at that, it would be my luck that the whole dang pickup fell off!
That has crossed my mind before, but I was thinking there would be oil to the lifters or the oil would look aerated. Now I just might have to crawl under her tomorrow and find out.
Thanks

Do you run a windage tray? My old Man had a problem with a big block he raced, in the upper RPM's the oil clung to the crank and the oil pump would scavange. Keep in mind this was a serious race only engine and the RPM was near 7500. He installed a windage tray and baffled oil pan, corrected that problem. What I have trouble with is the slack in the push rods, normally you set them when cold by pre-loading the lifers, if the lifters are pre-loaded where does the slack come from. I have broken valve springs as well and it could be felt across the entire RPM range. True they may not be strong enough, but why would it only show up once the engine warmed up. You have a unique problem.

you state after oil is hot lifter noise,,Also say the block should have a roller cam lifter so now you have flat cam lifter in block,,so are roller and flat cam lifters same dia on lifter and is block machining for oil to lifters same..sounds like lifter bore is to large and when oil is hot and thinner lifters bleed of from lack of enough preasure or flow to maintain...doc

Hey I just went from NEW GUY to WRENCH FETCHER is this place COOL or what. I think doc41 may be on to something here. If the oil galleys are high in the block they may not align with the lifters correctly. I know that the lifter bores are the same ID as I have used roller cams in non roller blocks. What I don't know is if the bores are the same depth, roller lifters are taller hence the shorter push rods. If the oil galleys are not matching up or if the lifter is to low in the bore, oil could be passing the lifters and returning to the bottom end as the engine heats up and things expand. I know of a real good engine machinest I'll point the problem at him and see what he says.

It's been raining cats and dogs all morning, so I haven't crawled under it yet.

There is no windage tray. And you're right that wouldn't really help in low rpm applications.

That was my mistake earlier, I forgot that I put the roller motor in my S10. This block has the fuel pump boss plugged by the factory, but is pre-roller. One of those kinda inbetween years.
Factory roller motors will usually have two or three bosses down the webbing rib above the cam in the lifter valley for the lifter hold down plate. The tops of the lifter bores are machined flat instead of having a little 'crown' and the face of the block is clearanced for the roller timing gear.

Good idea, buuuuuuuuuuuuuut..... the motor had a standard hyd. cam in it before I rebuilt it and it ran fine. Something obviously went south when I rebuilt it.

This just gets better don't it?!?!

And Tuts I know what ya mean, I'm almost to my 100th post. Whooohoooo!

"Factory roller motors will usually have two or three bosses down the webbing rib above the cam in the lifter valley for the lifter hold down plate. The tops of the lifter bores are machined flat instead of having a little 'crown' and the face of the block is clearanced for the roller timing gear."

some of the pre-roller blocks were built that way too (around 87-88) so the lifter bore "problem" isn't a problem...

do the lifters get there oil thru the cam bearing if so maybe not installed correctly...doc

Actually, I hope the cam bearings are put in wrong.........That just means I didn't screw anything up!

It's actually a beautiful day today, so I might get a chance to pull the pan and start snooping around.

At this point I'm not sure if I will sell or keep my blazer. I've owned it for 4 years and tried to sell it probably 100+ times. For some reason I just can't bring myself to part with her! It drives like a tank, sucks gas like there's no tomorrow and big tires are expensive.

But nothing beats the feeling of looking down on all these import loving kids and wondering if I ran them over, would I even feel it?

Based on my past history with this beast, I know I won't get rid of it, especially since so many of you have helped with this problem.

Thanks again, I update yall soon!

I missed it if someone else already mentioned it, but did you put heavier valve springs in? That with stock type lifters can cause them not to stay pumped up correctly at higher RPMs.

If the valve springs were weak, I wouldn't think the lifters would be giving out.

I'm still running factory springs. They maybe only have 50K miles or so on them. Although mileage doesn't really mean much because I've had em crack on right out of the box before.

Almost got the pan off, but Mrs Rust Bucket whipped out the honey do list. :mad:

For heaven's sake guys, get this thing figured out; the suspense is driving me crazy.

Shoot it and put another engine in.
...There, figured out.

This is kinda starting to read like one of them daytime tv stories isn't it?

Wouldn't you know it, no honey-do list today and it raining! Trucks way to big to fit in the garage.

Hell shooting it really doesn't sound like a bad idea.............

You were talking about the cam bearings being installed wrong. If this is the case you would have no oil or very little to the top end. I know this is going to sound strange BUT I may have an idea. On late model Dodges(I know this is not a Chevy) 318-360, there has been a problem where the oil doesn't return to the pan. The intake manifold creates a vacuum and holds the oil in the valley. This only happens in the mid-upper RPM's. The problem there is solved by opening another return to the bottom end. The only issue here is that on the Dodges it shows in a drop in oil pressure and yours is fine. I'm still scratching my head on yours though. :confused: I don't think I'd go Dirty Harry on this thing yet. :p

I had something strange happen to my 427 when I first put it in the Corvette. It was a Speedomotive crate short block. It always had normal oil pressure, but after a few hundred miles, a wrist pin seized and ripped apart the forged connecting rod, which shot pieces out the oil pan.

Upon open-heart surgery, my machinist discovered that a piece of wood had been shoved and wedged up in the oil galley, AFTER the oil pressure sensor, so that while my oil pressure always looked normal, I was starving my bearings until the engine finally broke. And it broke quite suddenly.

Yes, Speedomotive bought me everything I need to rebuild my engine again, once I mailed them a letter threatening to sue them. They theorized that they had a disgruntled worker in their place that sabatoged some of their crate motors.

I'm not saying that's what's going on here, but I have seen strange things like that happen. And it had us scratching our heads until we got to the cause.

True, because then I'd be fixing a rattle and a HOLE or two. Then again atleast the hole would be obvious

That is something to think about but this annoyance has shown up only after a rebuild. The block is the same I had been driving for years ,and the heads were ones I was using on my Nova for the longest time without any problem from either.

I think the Dodge problem was a casting issue in need of a little more clearancing. But thanks for the idea its not strange, my stupid motor is strange!

Looks like the driveway is drying up, hopefully I can get out there before getting roped into something else.....again..........

Thanks

awe darn, thats where my toothpick went!

You'd never suspect anything -after- the pressure port! That's scary.

That's something that's driving me insane. I wish this stupid thing would just blow up already! Most problems that I've had have made their presence known my creating a 'window' in my block.

I guess the problem with this one is that it still runs.And I'm afraid of digging a little too deep. But then agian, I did just find a decent machine shop up here in case I have to start over. Hmmmm I do have a 400 sb sittin on the shelf..........

Just a question, when you changed cams did you install new lifters? I have reused lifters on occasion(money,time)and have not had any real problems. If the problem started with the previous cam and had the same lifter that may be something. If the cam bearings were installed wrong during the rebuild it should have shown up during the break in. We are assuming that the timing is correct and the timing chain was installed right. Do use think you could be 1 tooth off on the distributor? It still seems like a detenation problem. Does it do it while in park and RPM's up or just under load?

Tuts, I did replace the lifters with cam. I have reused lifters before too, but had one eat a good cam and after that I always replace em.

This thing has rattled for a long time and I just chocked it up to timing. The day I was moving to Michigan is when it sounded like it dropped a lifter. In a panic I ran down to my old hotrod supplier and grabbed a new cam. I expected to see a lobe ground off or a 'cupped' lifter.......NOTHING!

After a world record time for cam install, It was still doing it. The only thing that changed was now my wallet was lighter. I even had my buddy who is a GM master mechanic come over and take a look . He double checked my timing, readjusted the valves, drove it, checked the timing chain, readjusted the timing again and was scratching his head too. It ran great by itself. But as soon as I hooked my trailer to it.....CHATTERING LIKE H#LL! My trailer is only 1400#s and maybe had another 1000 on it. As long as I ease into the throttle, it's fine until I reach about 2500 rpms. If I stand on in from a dead stop, valves float.

This is fun aint it?

It may well be that your springs aren't strong enough. If they are stock they may not have enough tention to hold the valves closed under load. It might be worth your effort to contact the cam manufacturer to see what specs they recommend on the springs. Your shop guy should be able to measure your spring tention and see if it's close. If you have good oil pressure(lifters bleeding down) and your not popping back through the carb or the exhaust under load(timing)your only left with the valve springs. This would account for the valve float and maybe even your being able to bottom out the rockers. If the springs aren't strong enough the valves may be opening when you bottom out the rockers and not the lifters. I can only think of one other cause and it would affect the whole RPM range, the rocker studs may have backed out. I don't believe this is the problem though. Still scratchin' :confused:

Are you running a HEI, I found that HEIs have a tendency to add timing as rpm rises, beyond where you set your total timing. Just a thought.

Sean

LADIES AND GENTLEMEN ........................


DRUM ROLL PLEASE............................

And the winner is......... 4onthefloor

Can you believe it, all this time I have been looking for problems on the top end when it was actually originating from the bottom. Sure enough, I drop the pan, and the pick up was sitting in the bottom of it.

I always weld the pickup to the pump, but the weld apparently broke on one of my muddin trips. I must have bottomed the truck out at some point because the pan was slightly dented on the bottom. I put the pickup back in and lined up the broken weld. When I tried to put the pan back on, sure enough it was about a 1/2" shy of the block which is about the depth of the dent. Bang the pan back out, weld the pickup back on with my handy dandy miller 250 and voila! Any question why I have since added a skidplate. Another big ol redneck truck back on the road!

The only difference That I notice now is that the oil pressure hits 60 lbs as soon as its started. Normally at startup it would be at 30 lbs and as rpms picked up then it would hit 60. This seemed fine because you only need 7 lbs/ 1000 rpms so I thought I was fine.

Well that explains it, at low rpm the oil is still pooled around the pump and as rpms increase, the pump was cavitating so the lifters were actually starving. :rolleyes:

I really want to thank everyone for your help and ideas!!!!!!!!!!!!!
But it might have been more fun to shoot it

Thank you!

As a reader of this thread, I learned something about oil pickup and "pinging".
I didn't know that.

Thanks for sharing!

Thank goodness you solved it when you did. I was ready to blow a head gasket and suggest you go buy a factory crate motor!

At last!! I was getin' a raw spot on the back of my head from all the scratchin'. It's always something simple that gets you in the end. Lets just hope you haven't done any real damage to the top end(I'll cross my fingers). At the least this has given me some distraction from whats going on over here. "BOLT UP" (Three smiles way up)

Well, so far so good. I did get a little scared though because there was traces of water in the pan, radiator was very low and the exhaust was steaming. Not to mention what sounded like a rod knock. After all of this,I was afraid that the block might have cracked from sitting through the winter up here.

I just let it idle for a while and then took it around the neighborhood and beat the snot out of it. Luckily it must have just been condensation in the muffler because it eventually burned off and the knock worked itself out.

Like I hoped, it was something stupid. I think if the oil pressure dropped that would be the first place I would have looked. Hopefully all of these symptoms will help someone with their project some day.

I can't thank yall enough for your help and support!

Thanks again
Scott