Cam Bearing Problems/Questions

[jt1]

About 3 weeks ago at a open track event, I experienced a noticable drop in oil pressure when the motor was hot. It was normal cold, but after a run when the motor was really hot, the oil pressure was dropping to about 20 psi. Upon pulling the motor and tearing down, I found this:

 

 

This was taken with the motor upside down, with a mirror lying in the cam tunnel. Hard to get a good pic, but generally the bearings look somewhat worse than the pic suggests. Lots of wear, with big chunks of material ripped from the bearing surface.

 

Some history:

 

1) This is the third time this engine has eaten the cam bearings, each time with about 1 yr/3500 miles of track use, with a few street miles thrown in.

 

2) Each time there has been some other contributing factor, broke pump pickup, broke rocker rollers, and third item noted below.

 

3) This has occured with three different cams, so the cam doesn't seem to be a common factor.

 

4) The last time I freshened the motor, I carefully checked the oil passages, running a soft copper wire thru them, and squirting oil in them and blowing compressed air to shoot the oil out. No obstructions I could detect. Oil hole in the bearings are properly aligned.

 

5) Bearings have been installed by my machinest, pretty sure they are the Durabond brand.

 

6) Melling M55HV pump, Mobil 1 15-50 after breakin.

 

7) Along with the oil pressure drop, the motor was running noticably hotter than normal, despite mid-70's ambient temp.

 

The contributing factor this time, discovered during the teardown:

 

 

This may have been a factor in the low oil pressure, but I can't really see it affecting the cam bearing situation. However, I was pretty fortunate not to scatter the whole show all over the track. The crank, rod and main bearing all still look like brand new.

 

Anybody got any thoughts or opinions on what's causing this? I'm somewhat disgusted with this engine, and am about ready to dump it behind the barn and build a whole new one.

 

John

[grumpyvette]

duplicate

[grumpyvette]

well the first thing Id suspect as a contributing factors are a combination of the high viscosity oil "that

"Mobil 1 15-50 " (as a 10W 30 is slightly more likely to flow thru and keep the bearing clearances supplied with enough oil to COOL the bearings.) and high valve spring pressures placing a significant load on those cam bearings

 

let me point out this chart

 

 

 

 

now obviously theres other factors,and since I didn,t build it or check the clearances I can,t really find the cause without knowing a good deal more , and that cracked main cap tends to make me suspect vibration/ballance and crank alignment problems are also involved, and your thinking about starting over with a differant block may be a good valid idea.....but ID strongly suggest a AFTERMARKET block as they are a good deal stiffer/stronger

[jt1]

Grumpy, thanks for your input. A few more factors:

 

1) I've used the M1 15-50 because of the temps the engine sees. In the summertime, 230deg water temp isn't uncommon. I don't have a oil temp guage, but it's bound to be approaching 300deg.

 

2) The engine was line honed two years ago, the previous freshen. We squared the decks and zero decked it, and my machinist likes to line hone before squaring the decks. Mains were set at 0.003, rods at 0.0025. We didn't check the cam brg clearances. The rod and main brgs still look great; they barely are shiny.

 

3)The rotating assembly was balanced by a very reputable shop when the engine was originally built, five yrs ago. The engine is internally balanced, I'm using a 6- 1/4" Fluidamper, and the clutch and flywheel balance was checked.

 

4) Valve spring pressures are moderate but not huge, Comp 977's, 150# seat, 420# nose.

 

5) The three center brgs are by far the worst, the pic is #4. The F&R bearings show some wear, not as much as the centers, and the F&R bearings don't have the chunks ripped out like the pic.

 

6) The two pieces of the main cap appear to have still been mated to each other; There aren't any shiny areas indicating the pieces were working.

 

jt

[jt1]

Well crap. The bell has tolled for this block. An afternoon playing with my recently purchased sonic tester confirmed something I've suspected, that this block is a POS. While all the thrust sides checked pretty good at 0.200 to 0.250, the sides are very thin, most less than 0.100, quite a few at 0.050 to 0.060, and one spectacular side in the 0.050 to 0.035 range. This engine has never shown the ring seal I thought it should, despite careful clearances, end gaps, etc. It's always had some blowby and oil consumption, and this confirms why. If anybody's interested, I'll post up the whole sheet showing the wall thicknesses. I'm going to hunt a better block and start over.

 

hecho en mexico, indeed.

 

jt

[280zwitha383]

 

Well that's a pretty nice piece to hang on the Wall of Shame. How much power were you putting through the thing?

[jt1]

In it's current configuration, it dyno'd 480hp/465tq at the crank, a pretty good pump gas 355.

 

Especially with the cylinder walls bulging like Roseann's belly at a buffet.

 

jt

[grumpyvette]

http://www.donovanengineering.com/Blocks/SmallBlock.html

 

http://www.worldcastings.com/newstuff3.html

 

http://www.dartheads.com/sbclittlem.aspx

 

http://www.brodix.com/Alum%20Small%20Block.html

 

http://www.gmgoodwrench.com/perfpartsjsp/partlist.jsp?cat=9370&section=ep

 

http://store.summitracing.com/partdetail.asp?part=DRT%2D31112232&N=400333+312759+115&autoview=sku

[dr_hunt]

And what is your idea of proper cam bearing installation as far as the oil hole is concerned?

 

Just FYI, dart uses a three oil hole cam bearing, one hole at 10AM, one at 2PM and one at 5PM looking at the front of the block with the intake side up.

 

Oil can't form a wedge when the oil hole is at the 6 o'clock position, it needs to be prior to loading at the 2 o'clock position. I've experienced some problems in SBC's in the past that was related to cam tunnel bore misalignment, did you check that?

[jt1]

Doc, the holes in the front bearing are at 12 & 4; the three center bearings at 2, and the rear at 12. This is the only way I've seen them done, I checked the passages to make sure they were open.

 

A new cam with new bearings spun freely with no tightness or binding, about the only way I can check the tunnel alignment.

 

John

[v80z]

Excellent thread guys. Watching very closely and very interested. Please JT let us know what and how the new build goes.

[dr_hunt]

You need a thin straight edge to check cam tunnel straightness or if the block has been align honed, you can measure from the main saddles down to the cam bearing saddles. A cam turning freely in the bores doesn't mean much since the cam was probably lubed. You could have .00025 clearance on one journal and .0025 on the rest and never know it. At least that's been my experience. I had a 400sbc that was trashing bearings in 20 miles, same thing, cam turned fine, oil holes proper, etc. Finally, after the second time I sent it up to Edwards and had them check it, it was out .002 from front to back, cam tunnel bored it, never had another problem.

 

This type of problem is precisely why I go dart blocks, I think I ended up with $1500 in machine work in that block by the time it was all said and done.

[v80z]

Man jt1 I took mine down to ground zero after reading this thread. I am glad my cam bearing were ok. Do you think the machining was off when it was bored? IS that what you mean by "not Squared". see my thread I am in a similar thrashing.

[jakeshoe]

And what is your idea of proper cam bearing installation as far as the oil hole is concerned?

 

Just FYI' date=' dart uses a three oil hole cam bearing, one hole at 10AM, one at 2PM and one at 5PM looking at the front of the block with the intake side up.

 

Oil can't form a wedge when the oil hole is at the 6 o'clock position, it needs to be prior to loading at the 2 o'clock position. I've experienced some problems in SBC's in the past that was related to cam tunnel bore misalignment, did you check that?[/quote']

 

SBC OEM blocks have a grooved oil supply to the cam bearings, so cam bearing placement as far as clocking is not critical. Most machinists install the holes lining up with the main bearing holes (6 o'clock as described) for ease of checking proper fore and aft placement of the cam bearings.

[jt1]

Do you think the machining was off when it was bored? IS that what you mean by "not Squared".

 

I'm not sure. My machinest wants me to bring it over and check it out some more. The only way I checked it was to make sure the cam was free. In my years of hot rodding, this is the first time I've seen a motor eat cam bearings like this. It sounds a lot like what doc is describing.

 

"Squaring a block" is a machining process. First you line bore/hone it to make sure the mains are straight, then a milling machine that indexes off the main bore and cam bore is used to machine the decks. This ensures that the decks are parallel to the main C/L, the same height form the main C/L, and 90deg to each other. "Zero decking" means the height of the deck and the top of the pistons at TDC are the same, which improves compression and quench.

 

NONE of this explains why it broke the main cap.

 

John

[dr_hunt]

Well, stuff happens, could have been worse. When encountering problems such as this it is often wise to scrap the block even if the main wasn't broken and start anew since the time, $$$ and aggravation are often not worth it. Stock blocks are fine for the most part, but like grumpy says, the aftermarket blocks are better.