Excess oiling in the rocker shaft/rocker arms 1500 BLMC
- Thread starter March 79B
- Start date
Acme Speed Shop
Well-known member
Jerry , this is the exact opposite problem most folks have with this engine, hence the the use of the external oil line used on those engines to increase oil to the rocker arms. I think the most sensible choice would be to make a limiting bushing for the oil feed hole in the rocker pedestal. Of course if this engine has the external oil line set up, you might just try eliminating it first. Hope this helps.
Aaron Johnson
Well-known member
that is an interesting problem. I've never had an issue with oiling on my 1500. always just enough up there to do the job. I know people use the external line, but not sure why.
something else might be wrong if there's too much oil up there and no internal line.
something else might be wrong if there's too much oil up there and no internal line.
Ron Bartell
Well-known member
How or why do you consider it to be too much oil? You don't say what level of tune your motor is, but in a race motor you want plenty of oil getting to the valve springs and rocker arms. The only way that you could considerate it to be too much would be if it didn't drain fast enough and filled your valve cover. If that is the case figure out a way to get the oil to drain faster. Bigger holes maybe? I know that we open up the holes on the 1275.
jandjracing
New member
Hello. I'm the person who caused this posting by march79B. I'm building the engine in question and it's for racing purposes and has had extensive work done to it. This 1500cc BLMC will become a race engine. This engine has an external oiling line to the back of the head. It also has roller rockers with needle bearings. I believe this is where the excess oil is coming from. The oil drain back passages in the head are as large and smooth as possible. Having trouble with rocker cover and cap seal leaking oil. Crank case pressure OK. I hope this info helps everyone, thanks, James
Gary Wittman
Well-known member
When I first started building my 1098 engines, I found I was getting to much oil to the roller rockers with needle bearings. The needle bearings seem to let the oil pas through much faster than bushing style rockers. I installed a restrictor bushing in the oil feed pedistal. I don't remember the size of the hole in the restrictor but I don't think it is more than 1/16th inch. I have run this system since around 1988 without any valve train problems that cold be attributed to oil starvation.
JohnMcNaughton
Well-known member
"Having trouble with rocker cover and cap seal leaking oil. Crank case pressure OK. "
You indicate that the evidence of leaking oil is around the rocker cover and cap. Have you tried changing gaskets. I won't mention that I always thought that was how you knew you had a BMC engine. If the area under the valve cover is filling wth that much oil, you might be loosing oil pressure/volume supplied to the crank area!
Check for an oil restrictor in the oil feed system to the head, is it in place or missing? Race engine valve springs develop a lot of heat from their operating conditions, high spring pressure, sustained high RPM use, sustained engine heat. I have used all types of oil restrictors, in all types of engines, from using a screw in carb jet to a small crushed metal tube with a length safety wire used to create the jet size.
Have you checked the venting system for blockage? Is any oil gathering in the oil catch can?
You indicated that the engine already had some extensive work done to it and a head oil feed system already installed. That implies that at one time is was possibly working correctly. Contact the person that built the engine/head for setup information.
You indicate that the evidence of leaking oil is around the rocker cover and cap. Have you tried changing gaskets. I won't mention that I always thought that was how you knew you had a BMC engine. If the area under the valve cover is filling wth that much oil, you might be loosing oil pressure/volume supplied to the crank area!
Check for an oil restrictor in the oil feed system to the head, is it in place or missing? Race engine valve springs develop a lot of heat from their operating conditions, high spring pressure, sustained high RPM use, sustained engine heat. I have used all types of oil restrictors, in all types of engines, from using a screw in carb jet to a small crushed metal tube with a length safety wire used to create the jet size.
Have you checked the venting system for blockage? Is any oil gathering in the oil catch can?
You indicated that the engine already had some extensive work done to it and a head oil feed system already installed. That implies that at one time is was possibly working correctly. Contact the person that built the engine/head for setup information.
I have zero experience with BMC A engines*, but I think Gary has hit the nail on the head. Most (all?) production "rocker arms on shaft" use sleeve bearings (or just an iron rocker on a steel shaft, same thing) in the rockers. The 1 or so thousandth clearance between rocker and shaft restricts the oil flow, so the inside of the sahaft will fill with oil and the flow is "metered" at each rocker. Many engines (stock anyway) will additionally restrict the flow to the saft.
A needle or other rolling element bearing is "mostly air" - and there will be a fairly unrestricted path from the shaft interior out the feed hole to the interior of the head. Depending on the flow characteristics upstream this could hurt the overall oil pressure, flood the head, starve the rockers at the other end of the shaft from the feed, etc. So what sounds right to me is to use small feed holes at each rocker (for rolling element bearings) that meter a little oil into each one.
No idea as to the correct size or whether other parts (valve springs etc) need more oil. The needle bearings won't need a huge amount of oil but do need a steady flow of "some". (I doubt that engines spinning at less than a billion RPM (ie 948s) need to worry much about cooling the valve springs..??)
(My rocker arm engine experience is with Datsun R16 which is allegedly similar)
A needle or other rolling element bearing is "mostly air" - and there will be a fairly unrestricted path from the shaft interior out the feed hole to the interior of the head. Depending on the flow characteristics upstream this could hurt the overall oil pressure, flood the head, starve the rockers at the other end of the shaft from the feed, etc. So what sounds right to me is to use small feed holes at each rocker (for rolling element bearings) that meter a little oil into each one.
No idea as to the correct size or whether other parts (valve springs etc) need more oil. The needle bearings won't need a huge amount of oil but do need a steady flow of "some". (I doubt that engines spinning at less than a billion RPM (ie 948s) need to worry much about cooling the valve springs..??)
(My rocker arm engine experience is with Datsun R16 which is allegedly similar)
Protech Racing
Well-known member
I would think that it would be better to drill each rocker shaft hole to size, bigger near the ends. This would keep the shaft full and under pressure distributing
oil exactly where needed.
Restricting the oil at point of entry may allow the shaft to not be full and at much lower pressure.
I ¨dimple¨ the head surface to grip the gaskets better. Not just for British cars but VW , chevs etc.
oil exactly where needed.
Restricting the oil at point of entry may allow the shaft to not be full and at much lower pressure.
I ¨dimple¨ the head surface to grip the gaskets better. Not just for British cars but VW , chevs etc.
Mike -
Absolutely, if using rolling element bearings the restriction should be at each bearing/rocker, keeping the rocker shaft full.
I'll quibble a bit and say that if the individual restrictions are as small as they should be, and the supply to the shaft interior is ample, then the shaft will be full, pressure drop along the shaft almost none and therefore all holes can be the same size.
As an anecdote, I found out the hard way that:
A) It is possible to install the rocker shaft of the Datsun R16 such that the oil feed hole seems to be lined up but isn't
and
B) that a GP Datsun will run about 2 laps at Charlotte with just the assembly lube (plus oil poured over during filling) lubricating the valvetrain in the head
and
C) that the rockers, springs, retainers, shaft etc turn a rather dramatic dark blue when really really hot
Some WWI airplane engines flew for hours like that but I guess that's a difference betweeb 1800 and 7200 RPM.
Absolutely, if using rolling element bearings the restriction should be at each bearing/rocker, keeping the rocker shaft full.
I'll quibble a bit and say that if the individual restrictions are as small as they should be, and the supply to the shaft interior is ample, then the shaft will be full, pressure drop along the shaft almost none and therefore all holes can be the same size.
As an anecdote, I found out the hard way that:
A) It is possible to install the rocker shaft of the Datsun R16 such that the oil feed hole seems to be lined up but isn't
and
B) that a GP Datsun will run about 2 laps at Charlotte with just the assembly lube (plus oil poured over during filling) lubricating the valvetrain in the head
and
C) that the rockers, springs, retainers, shaft etc turn a rather dramatic dark blue when really really hot
Some WWI airplane engines flew for hours like that but I guess that's a difference betweeb 1800 and 7200 RPM.
Charlie Tolman
Well-known member
I believe that Gary and Al are correct on the topic.
A rocker arm with a bushing, due to its tight clearance, will flow a small amount of oil.
A rocker arm with a roller bearing, due to its open structure, will flow a large amount of oil.
Using an electrical analogue, a bushing has a high resistance, so the current (flow) is low, and the voltage (pressure) is high.
A roller bearing has a low resistance, so the current (flow) is high, and the voltage (pressure) is reduced.
I would hope that manufacturers of roller bearing rocker arms would supply a rocker shaft with smaller holes for each arm, as
compared to the hole size for rocker arms with bushings.
If the flow through the roller bearing rocker arms is high enough, with a corresponding oil pressure decrease, then there might be other areas in the engine that could experience reduced oil pressure ?
Charlie Tolman
A rocker arm with a bushing, due to its tight clearance, will flow a small amount of oil.
A rocker arm with a roller bearing, due to its open structure, will flow a large amount of oil.
Using an electrical analogue, a bushing has a high resistance, so the current (flow) is low, and the voltage (pressure) is high.
A roller bearing has a low resistance, so the current (flow) is high, and the voltage (pressure) is reduced.
I would hope that manufacturers of roller bearing rocker arms would supply a rocker shaft with smaller holes for each arm, as
compared to the hole size for rocker arms with bushings.
If the flow through the roller bearing rocker arms is high enough, with a corresponding oil pressure decrease, then there might be other areas in the engine that could experience reduced oil pressure ?
Charlie Tolman
Speaking from the A series BMC side of the house I would contact Harland Sharp in Ohio on anything having to do with roller rockers. Besides rockers for anything they make their own hardened shafts for proper oiling of whatever you have. We have two 948s and one 1275 engine with their parts in them and no problems. The 948s have been running hard since the late '90s (at 7 to 9,800 rpm Al) with recent rebuild and new shafts from HS. They are also free with their information and very nice to work with. Good info above... you just need to get the right numbers for your engine.
Bob
Bob
Ron Bartell
Well-known member
I never had the problem that Gary mentions with the needle bearings flowing too much oil. Clearly the roller rockers will flow more oil past the needle bearings, but the holes to and from the rocker shaft are small on the 948/1275 motor so there were no changes needed when we made the conversion from bushing-style to needle bearings on the A series motors other than going to harder rocker shafts. That assumes that the aftermarket suppliers of the shafts didn't make a change. I know that as an end user we didn't have to modify anything.
Again, the OP didn't state what he means by too much oil. Is the valve cover filling or are you just getting a leak past the gasket. What we do to help with that is to do a good job of gluing the gasket to the head, rather than the valve cover. This allows the valve cover to have a small amount of oil pooling up in the cover without leaking, and for me was all I ever needed to deal with the extra oil. We use Super Weatherstrip Cement.
Bob - I've seen you post 9800 rpm for the 948 motor now a couple of times. It could probably do that once
, but having run that motor for over 30 years I would say that you need a new tach.
Again, the OP didn't state what he means by too much oil. Is the valve cover filling or are you just getting a leak past the gasket. What we do to help with that is to do a good job of gluing the gasket to the head, rather than the valve cover. This allows the valve cover to have a small amount of oil pooling up in the cover without leaking, and for me was all I ever needed to deal with the extra oil. We use Super Weatherstrip Cement.
Bob - I've seen you post 9800 rpm for the 948 motor now a couple of times. It could probably do that once
, but having run that motor for over 30 years I would say that you need a new tach.Ron... Tach is a cable drive Jones that has just recently had a rebuild. Dave Taber, Harland Sharp and Jon Stamps built these engines to run between 7,000 and 9,500 rpm. They dyno at 98 hp at 9,500. Don't come on the cam until 7. After I bought the car in '03. It took me at least 6 race weekends to get used to the fact that the tach was turned with the 7k rpm in the 11 o'clock position and I wasn't going anywhere until it was turning over 7k. The two engines will not run below 3,500 and are hard to keep running there. Can't dispute the power they pulled out of these engines with dime and quarter valve sizes. Still harder to believe is the cranks keep Mangnafluxing good because they are knife edged, lightened, balanced STOCK cranks. When one of them grenades I'll post it for you. Forgot... the cranks were nitrited and we are still using STD bearings on them. Don't ask me, I just keep on driving them. Had them above 10k a couple times and they are still here. Gotta love Dave Tabor! Back to the faulty tach... we have a small ohm meter on the dash that monitors the Electromotive advance. It's set to bring the advance down from 35 at 4k to 30 at 8k. Meter is right in front of my face next to the h20 gauge and it also tells you where the rpm is. The combination of the two saved an engine on a warm up lap when the electromotive high advance side died and ran the advance up to 68 at 6k. Tach said 6k, Electromotive said "grenade time!".
Bob
Bob
Dennis Shaw
Member
If you are having oil pool in the cover I suspect you are having an issue with the crankcase pressure and the oil having to use the same passage way but they want to go in opposite directions.
I would suggest you add another passage way for the crank case pressure to travel.
If you could use like the mechanical fuel pump attach point to add a "duct" or hose to vent blowby to the top of the engine or catch can so the oil can flow down unimpeded around the push rods or the drain passages.
Back in the 70's our IMSA AMC sixes had a similar issue. we used a spray bar to lube the rockers and cool the springs. I used the mechanical fuel pump block off plate to add a breather from the low side of the engine and our issues went away.
I simply added a stand pipe and put a GM breather cap on it. Done!
I would suggest you add another passage way for the crank case pressure to travel.
If you could use like the mechanical fuel pump attach point to add a "duct" or hose to vent blowby to the top of the engine or catch can so the oil can flow down unimpeded around the push rods or the drain passages.
Back in the 70's our IMSA AMC sixes had a similar issue. we used a spray bar to lube the rockers and cool the springs. I used the mechanical fuel pump block off plate to add a breather from the low side of the engine and our issues went away.
I simply added a stand pipe and put a GM breather cap on it. Done!
Ron Bartell
Well-known member
:lol: I'd still look into a new tach.Bob Hess":2vep1xsj said:
Ron... Test meter confirms tach every time. You just ran Sebring in the Jan Majors, do some math. Trans 1.8, 1.4, 1.2 and 1.1. Rear 4:55. Tires 20 x 8 x 13. 8,400 to 8,800 at the end of the back straight approaching 17, out of 17 in second around 8,400 (depending on not hitting oil and kissing a wall like we did last year), shift to third around 9k etc.
Back to original subject... both engines have dual oil drains from the lifter gallery down to fittings on the pan to compensate for the small drain areas in the block.
Bob
Back to original subject... both engines have dual oil drains from the lifter gallery down to fittings on the pan to compensate for the small drain areas in the block.
Bob
Ron Bartell
Well-known member
Bob - I believe that you are providing some interesting entertainment for anyone who has actually raced these engines for years. A couple of points though: 1) Tough to do any math when you don't provide the top speeds for those portions of the track. 2) 8,400 to 8,800 is different from 10,000. 3) I noticed that you were running a 1275 at the Sebring race, not the 948. Do you actually run the 948's or just talk about them? (just kidding)