Stump the Wizard

[Bob Knight]

OK, I'm stumped and so will put it out for help from the more experienced.

Last year I bought B9471929. The car was formerly owned by Craig Angel and was extensively autocrossed. Like Warren said in an earlier post, race hard, wreck, repair, repeat. When I obtained it, it had been in storage for the better part of the past 10 years. PO had obviously done a lot of mechanical work on the car, and just as obviously had zero mechanical skill. I was going to completely restore it, but subsequently bought B9471705, which was a never wrecked, no rust car like I'd been searching for for years, and which I've already completely restored just how I want, so now I'm just trying to get B9471929 back on the road as a running, driving Tiger. I got most of the issues sorted out eventually, but one has me stumped.

The engine is a built 302, 6 bolt block. Runs great, white smokes both tires for a good 50 to 75 feet, feels like it's going to pull a wheelie when speed shifting into 2nd, and will break the tires loose just by stepping on the gas in 2nd. (granted, 10+ year old hard as a rock tires have less than ideal traction)When I got the car, both motor mounts were broken and the motor was sitting quite low. The oil pan had obviously been hit hard on something, and had a big dent in it. The first time I got the engine up to normal operating temperature, once it got good and warm, the oil pressure dropped down to about 5 psi at idle and 10 to 15 at 1500 rpm. Oil pressure was normal 30 to 40 at idle and 50 to 60 at 1500 rpm when cold. ( I did the above mentioned burnout about 2 minutes before noticing the oil pressure dropping drastically)

I dropped the oil pan, and discovered that the dent was pushing the bottom of the pan against the pickup, and the pickup bolts were quite loose. I pulled the bearings and they were right down to the copper on the bottom of the mains and top of the rods, with the slightest hint of tin remaining on the opposite sides. The crank was .010/.010, still in good shape with no scoring or marks, and mic'd within tolerance. Bearings were .010/.010 as well. I noticed that some of the rods were installed backwards (chamfer side to the center), and a couple had the caps backwards on the rods. I couldn't get the rods to pivot without dropping the crank, which I was reluctant to do (and is probably impossible with the engine and trans in the car) and so I left the backwards rods the way they were, I didn't notice any scoring on the outer radius of the crank journal so they must have still had just barely enough clearance.

I put in a new set of .010/.010 bearings, checked the clearences with plastigage, all within tolerances, installed a new high volume/high pressure oil pump, new pick up screen, new heavy duty pump driveshaft, red loctite on the screen and pump screws, new oil pan. Put everything back together with a fresh filter and fresh 20/50 oil, started it up, warmed it up, and..... exact same symptoms. Except that now the high oil pressure when it's cold is more like 80 PSI and it drops to 20 when hot. Valves seem to be adjusted within tolerances and it runs perfect except for the oil pressure problem. Yes, I checked to make sure the oil was going the right direction through the aftermarket adaptor and remote filter.

Any Ideas? Short of removing the motor and doing a complete overhaul? And even then I'd like to have SOME idea of what I was looking for.

Bob Knight
B9471705
B9471929

 

[cobrakidz]

This may be way off the subject for your fix BUT I had a new crate motor 350 in my last street rod--it had great oil pressure when cold and when it got warm the pressure was about 5 psi at idle. I called the dealer and he explained that's how their new motors were made to operate and that I was not to worry about it being that low. I don't know if the pump made the difference or the bearings/oil passages. Maybe try another pump???

 

[Twin Turbo Tiger]

I would pull the motor and check all clearance's and check the cam bearings,
You can run it like that but I like to see my SBF with good oil pressure when cold and hot.

 

[HolyCat]

Did You Check the Oil Gauge?

Bob,

I know this is obvious and you probably already considered it, but have you checked your oil gauge for accuracy? Or try a second gauge to see if you get the same result, or the original gauge in a different car?

 

[Bob Knight]

Oil Gauge

Yea, I checked the gauge, went to auto parts and bought a cheap mechanical gauge. It showed less oil pressure at idle than the stock gauge, although the face markings weren't nearly as precise as the stock gauge. Just to be sure I took off the line and held my finger over the end as well - couldn't feel hardly pressure, although the oil sure was hot...

I thought about the cam bearings, my brother, who builds Baja race trucks and has considerable experience tearing down beat to death small block Ford engines, told me that generally the cam bearings look about like the mains in terms of wear. So, if the mains were down to the copper, that means the cam bearings probably are too. Would that be enough gap to drop the oil pressure that drastically? That was one reason I got the high volume pump. I think changing the cam bearings with the engine in the car would be difficult to impossible.

Sigh... guess I'm pulling the engine. If I take this engine out, I'm seriously considering restoring the car back to stock. B9471705 has a more powerful engine and I don't really need two hot rod Tigers, and it appears that the bone stock Tigers are the ones that are starting to bring the best prices.

Bob Knight
B9471705
B9471929

 

[Doctorbugz]

Bob,
It sounds like that engine was run hard and put away wet too many times, compounded with oil starvation from the pan/pickup issue. Autocrossing is brutal on internals, the constant on/off and hard shifting in the lower gears transmits huge amounts of impulse energy back through the drivetrain into the engine's rotating parts, and constant over-revving stresses rods and valve train. All this can cause the crank to twist and thereby distort the mains, cause the rod big-ends to distort and become egg-shaped, and the cam bearings and lifter bores to wear. The bearings simply are too distorted to flow oil correctly and installing new shells doesn't help much. Add some slop in the timing chain and the top end issues get worse. If your lifter bores are worn the block is toast.

If you saw rods installed incorrectly then someone who didn't know WTF they were doing had gotten deep into that engine. Who knows what else they screwed up? I have seen normally worn engines that had similar low pressure issues come back to normal when a high volume pump was installed, but I think it's likely you have a more basic problem than just wear, especially since you used 20w-50 oil.

Did you replace the rod bearings as well as the mains? If not, do this test: get the engine up to temperature and standing next to it rev it to about 3K for a couple seconds, then quickly close the throttle and listen for knocking as the engine slows down. If you hear knocking or a little clattering as the rpm decreases you have a rod knock, and that is just no fun. The 20W-50 can mask this, I will drop the good oil and run a 5w-20 to do this test if I suspect there is an internal issue.

The SBF is a tough little beast, I've built several of them in stock and stroker configurations, if you use the right components you can flog them forever. But beating on an engine with stock cast crank and rods is just asking for trouble and it sounds like you inherited it. The risk is up to you, if all you are going to do is drive it on the street then it may be fine for years, but then again you may wind up with pieces-parts scattered at a stoplight tomorrow.

Since it's already been converted to 6-bolt you have many cheap choices to find a good long block and just swap it out, will be cheaper in the long run. In the mean time just run it until it blows!
Good hunting!
Bugz
B382000991 - 289
B382001465 - 331

 

[Bob Knight]

Bugz is probably right

Yea, Bugz is probably right. I did change both the Rod and Main bearings, and checked the clearance with plastigage, I didn't however, check to see if the rod bores were still round.... and I suppose the bearing shells are stiff enough the plastigage wouldn't notice if the caps were elongated. I do not hear any "loose rod bearing" noise, and I do know what that sounds like. I've also heard what a SBF sounds like when the oil pump driveshaft twists off and there's no oil pressure, never heard those sounds either. No rumbling grumbling, no noisy lifters. If it wasn't for the down-to-the-copper bearings, I'd suspect a crack in the galley that feeds the oil pressure gauge, and everything else is OK.
The thing runs so good, I guess if everyone thinks 5 psi at hot idle is marginally acceptable maybe the "run it until it blows" scenario is best. I'm really just trying to get it into reliable running condition to sell it.
My next idea was to try straight 40 wt oil. I did try the 5w30 that I use in the 331, it had NO discernable oil pressure on the gauge at hot idle with that.

Bob Knight
B9471705
B9471929