i have a rebuilt LT1 with about 15k. It has forged pistons and its 30 over. So im cruising at 80 on the highway and the oil pressure goes to zero. I pull the pan and tap the starter to see if the oil pump is turning and it does, so i pull all bearings with the motor in the car (****in hillbilly). The bearings are all perfect so i pull the intake and remove the oil drive gear and it is absolutely wasted. Do any of you think the melling high volume oil pump could have caused this. Maybe too much stress trying to turn that thing in a street car? Let me know what ya think...

 

What, am I all alone on this one???????????

 

What kind of cam did you put in it? I'm thinking possibly some incompatability between the 2 materials, of cam gear and oil pump shaft gear.

 

This condition is pretty typical of HV pumps. They are not necessary in a high performance small block. It is a myth that they are. Go with a high pressure, standard volume pump.

 

Gear breakage is definitely not typical.

Those may argue if a HV pump is necessary on an LT1 (which is a whole different topic), but there should never be a significant wear problem of the gear unless something else is wrong. I've built over 100 small blocks with out a single gear issue. I have quite a few out there with over 100K miles on a HV pump.

Did it grind the teeth into filings or are all the teeth broken off & laying in the pan? A locked up pump is usually the cause if they are broken & its gear alignment or heat treat issues if they are worn down.

Compatability is the main cause (as mentioned above) when the wrong type of cam is used. The drive gear can fail if it is already worn from a high mile motor..... these need replaced during a rebuild as well, but often overlooked. The new cam causes a different wear pattern on the old gear & cause failure

 

The cam was stock, but the teeth on the gear and cam had 130k so i'm assuming the extra tension from the HV pump wore the teeth. The car is completely stock besides being 30 over and shorty headers and a catback. On my bald tires I went 13.7 @100, Drag radials and a CAI are sittin in the garage, once she goes back together I should be around a 13.5.

 

I'm with you Lonnie, as I also use a HV or BB pump on all my high HP builds with no problems to date.

 

I think ya found your problem.... if the pressure and volume are not matched to the clearances then you can easily have this issue. Now add in there the cam tunnel can be machined inaccurately in comparison to the mains and now you have side loading.... OR maybe the endplay in the cam was not in spec, there is another force acting on the cam/oil gear interface and bam there goes the gear. If you require more out of the gear than the stock setup you can easily have a issue, especially with extra high cold oil pressure. This ain't just one thing that causes this, it's a few.

Bret

 

LR,
I've done the BBC pump in a small block before as well. Definitely overkill. I used it on a 7600rpm 2 bolt with a 250 shot of nitrous. I ran the pump to compensate for the large bearing clearances I was running to keep from pinching the bearings... It never broke even though you could see where the mains were moving around. Not something I would now recommend, but I did it when I could not afford good parts on a teenage income. Can't complain about 10's on stock rods & cast crank though.

Something overlooked is that the same distributor gear is used in a big block with a significantly larger pump.... so you cannot blame the extra volume of the pump.

If pressure kills them then a high pressure stock volume pump would hurt it as well.

Very high cold pressure is probable cause, but you should be using a thinner weight oil then. No need to run straight weight oil or 20w50 when thinner cold viscosities are available like 5w50.

The BBC pump in a small block would swell the oil filter & wrap the oil pressure gauge past 100 & back to 0 on a winter start up if you revved the engine. Learned that the hard way leaving for work on a cold morning when oil started leaking everywhere. It's amazing the stories you have after playing with cars for 20 plus years.

 

I blew a filter clean off the engine when experimenting with oil pump pressure spring shimming (when I was young, of course).

Whatever the reason, it seems like only people running a HV pump have trouble with the drive gear going away. Obviously, an HV pump can work well when actually needed and with the right supporting cast of parts and engineering.

 

Lonnie,

It's not the size of the gear it's the loads on it. A BBC oil system requires more volume as well. Think about the area of something that is .0030" thick but change the width and diameter of that. The volume of oil around the mains in a SBC is 2/3rds of that of a BBC, and the rods are around 4/5ths the volume, now add in there the cam bearing difference as well and now you start to realize why a BBC has more pump than a SBC does.

Bret

 

They do work well.
Ya need bigger clearances than most put in an engine to need it. A stock rebuild don't need one.
I like clearance so on a HP build I will run 2/2.5 on the rods 2.5/3.0 on the mains and most people don't build them that way. It has worked for me for a number of years so I will stick with those sizes.

The load to drive a BB pump is more than a SB pump due to the size of the gears but have run them in sprint car engines with a bronze gear for several years and have not had a failure. That same bronze gear is driving the mag and fuel pump also so I don't know what the problem is with the LT1 steel gears. Could be an alignment issue with where the cam is sitting, front to rear,don't know. It also could be a material compatibility issue. It also may be a lube issue to support the extra load. I always cut a groove in the bottom fit to allow pressure oiling to squirt on the cam gear.
Some are destroying the rear cam lobes on stock cams so the lube issue may be valid. Splash oiling may not be enough for the extra load.

 

Bret,

I understand the clearance/volume issue. If the volume of flow is less, the pressure will then be higher for the same pump until the bypass valve opens.

I am a mechanical engineer by trade & work for a major valve company so I deal with pumps, fluid dynamics & pressure calcs on a regular basis. Cars are my second profession.

My point was that the same pump no matter if it is in either a SBC or BBC, if it is developing the same pressure it will be seeing a similar load to pump the same fluid. My whole point was that the same distributor gear survives in a BBC with a high volume BBC pump which are approx. 30% larger than a SBC high volume pump. My own truck (w/ 427 engine) never drops below 50# at idle & bypasses at 80#. No gear problems ever.

Another thing to consider is that you can file a small groove in the oil pump stub with a triangular file (approx 1/32" wide & deep) from the oil groove down to the distributor gear (you will end up with an approx 3/8" long score in this area). This has to be done on the same side as the camshaft & distributor gear intersection. This will provide additional lubrication on this gear as well. Wish I had a picture to better explain this. If I can borrow a digital camera I'll take a picture of my LT1 stub with this mod. Currently doing a piston swap in preparation for more boost.

 

Another thing to consider is that you can file a small groove in the oil pump stub with a triangular file (approx 1/32" wide & deep) from the oil groove down to the distributor gear (you will end up with an approx 3/8" long score in this area). This has to be done on the same side as the camshaft & distributor gear intersection. This will provide additional lubrication on this gear as well. Wish I had a picture to better explain this. If I can borrow a digital camera I'll take a picture of my LT1 stub with this mod. Currently doing a piston swap in preparation for more boost

=====================================

As I mentioned above that groove is how I do it. MSD actually sell some with the groove.

 

That's why I said this....

Now add in there the cam tunnel can be machined inaccurately in comparison to the mains and now you have side loading.... OR maybe the endplay in the cam was not in spec, there is another force acting on the cam/oil gear interface and bam there goes the gear. If you require more out of the gear than the stock setup you can easily have a issue, especially with extra high cold oil pressure. This ain't just one thing that causes this, it's a few.


I think it's a lot of things that add up to cause this issue. Not to mention a cam with tappered lobes pushing things around.

bret