Dave Cunningham

I was following another thread a couple of weeks ago concearning the exact same problem that I have been having. Recently rebuilt L71, with maybe six or seven hundred miles on it, and it is gobbling up oil like it is going out of style. I estimate about a quart every 150 miles. After reading through all the posts on the other thread, I am pretty sure it must be the intake manifold, I tightened up all the bolts again, and did find one side to be a bit loose, but that did not fix it. When I installed the manifold the rear bolt on the passenger side started to pull the threads, so I just left it snug and figured it would probably be fine. I did machine the manifold to get clearance for the mounting bolts, but it seemed to fit perfectly, and still had a nice gap at the front and rear of the block. I have pulled the plugs , and the two rear plugs are black and oily, with the rest being a perfect tan color. I gues the next step would be to install a heli coil in the rear bolt hole and try to get some pressure there, but if that doesn't work, how would one fix the problem? Pull the manifold and goop up the intake ports with permatex or something? Also I can't understand how there would be no evidence of the consumption in the way of smoke, it is obviously getting sucked into the combustion chamber, but there is no sign of blue smoke out of the side pipes .
Speaking of consumption , the amount of fuel the car burns seems excessive as well, I did a rough calculation and estimate that it is probably getting about 5 miles to the gallon. I was reading an article by Duke Williams that happened to mention the fact that an internal combustion engine is obviously most fuel efficient when turning at the lowest rpm possible. Duke suggested for regular driving to shift at the lowest rpm possible and basically lug the car around in the highest gear you can get away with, and use the fuel you save for those times when you want to go blasting through the gears at redline. That made good sense to me so that is how I have been driving the car. I would think it would get a little closer to the factory advertised 9 to 12 miles to the gallon.
Oh by the way, I broke the car in on Joe Gibbs 10-30 break in oil, and am now running 15-40 Diesel engine oil.

65hihp

Duke is the original little old lady from Redondo Beach.
I don't know anyone who would want to drive a 67 L71 like he suggests.

SupremeDeluxe

I drive mine to MAXIMIZE my carbon footprint.

6T7L71CPE

Do you have the oil baffle under the intake? Did the mounting tabs clear the intake gasket? Mine once didn't clear and the intake didn't seal well.

cardo0

Well knowing the engine was a very recent rebuild suggests several possible problems.

Are the rings seated - u need to do this right away. U need to romp on it and run at moderate rpm over a short period. Like find a slow grad hill and run it up to 5000rpm and back down to at least 2200rpm a few times. Okay to let it cool down somewhat between pulls.
Now u can measure blowby but it aint a simple test. But to verify oil ingestion from the PCV only takes a small container with a inlet hose terminating close to the bottom and a outlet hose on the lid to act as an oil separator and u can see any carry over with this.

Next the intake may no longer match the heads. If the heads and or block were machined the intake now sits higher and the bolt holes no longer line up. U should be able to physicaly see this with intake sitting on the block. Now to verify oil leaks a flex digital camera will fit down the intake runner (once carb is lifted) and i bought my USB camera for $15 that works on a laptop or tablet. If intake leaks oil u should see oil on those rear runners.

High fuel consumption is the carburetor tuning. Could be anywhere from fuel pressure, inlet needle/seat, jetting to the choke operation.


Hope this helps.

Westlotorn

You mentioned the plugs look great in 6 cylinders and bad in the rear two cylinders, exactly where your stripped bolt exists.
This same engine had many overheat issues in an earlier post if I remember correctly.
I would pull the intake manifold now. Inspect the gaskets and intake ports very closely and see if oil has been seeping into the rear two ports. If they are clean and dry like the other 6 ports this is not your issue. If they are wet and oily you found the issue.
Fix the threads in the head and try install again. If you stripped the bolts you might have a bad torque wrench or used the wrong torque for the bolts. Or the head had a bad prior owner!
This will help your MPG but if you are at 5 you may need some carb tuning.
I am sure others on this forum with your engine can give you an idea what they could do.
I would expect 10 in town and 13-15 on the road.

Dave Cunningham

Good one Don, I of course don't want to drive the car like that, but the mileage is so horrible I thought I would try it at least.

Dave Cunningham

I hoping that I may be able to repair that bolt hole with the manifold installed and try to fix it that way, so that I can keep driving the car for the rest of the summer. As I mentioned , how would you solve the problem anyway, does someone make a thicker intake gasket?

Dave Cunningham

I would think the rings would have to be seated by now as it has been run for several hundred miles in all kinds of driving conditions. As I mentioned I did have the intake ( brand new reproduction ) machined to get the bolt holes to line up, and it seems to fit perfectly. I will try the tests you described, thanks.

Bluestripe67

If you did not breakin the engine standing still using the well established procedure on the first turn of the key, you may have damaged the rings dispite your statement of not seeing oil burning out of the pipes. I could be wrong, but! Dennis

Westlotorn

Normally Rings break in evenly on all 8 cylinders, this engine shows 6 working and two in the back burning oil. He also has a known problem with the intake manifold clamping force.
Pulling an intake is a pretty fast job normally, Maybe 45 minutes off, inspect, post pictures of what you see in all 8 ports and we can help.
It is very important if you have an aluminum intake that you use compatible intake gaskets. Aluminum heats and cools faster so it expands more than your head. The gasket material needs to allow for that movement or they fail. They usually last more than 200 miles though even if wrong for the application.
You would need a torque wrench for the installation and the bolt pattern to follow while you torque the intake back on.
If I remember correctly you are a highly trained distributor mechanic now and that installation is the only tricky part of your job.
Mark

Dave Cunningham

Your probably right Mark, I might as well bite the bullet and yank it off, fix the damaged hole and see what's going on in there. I used the best quality Felpro gaskets that I could get my hands on, what type of gaskets would you recommend ?

Westlotorn

Dave, I have been very partial to Fel-Pro, but I can't answer your question without more information. The big block has oval and rectangular ports and offers small and larger ports depending on your set up. Also need to know what manifold you have, Cast iron or Aluminum. Also available with blocked or open exhaust cross over. Are your ports factory or have they been opened up? Are the heads factory or aftermarket, if aftermarket what head design. Fel-Pro offers nearly 20 performance options and 2 factory stock replacement options.
Take a look at this website: http://www.fme-cat.com/PerfApplicati...20Engines&ga=Y

Jackfit

Same problem, last two bolts need to be torqued to spec. Problem will go away

427425

You could try to use a stud in the bolt hole that is stripped. There may be a couple of threads below where your intake bolt is reaching that will hold the stud and allow you to torque a nut to the proper spec. If this works, it will allow you to use the car until you have time to do the job. If you have to pull the intake, take the time to verify the angle on the intake side of the heads as well as the angle of the mating side of the intake. Either could be off a degree or more from front to back causing your problem. If it is small enough to be fixed with sealer, Ultra Grey Permatex is the toughest I have used for contacting oil and gas. I have used it in the oil pan of drag race engines without issue. Good luck!

Westlotorn

Silicones, even ultra Grey work outstanding with oil but break down in gasoline and gasoline vapor so they won't work with an intake manifold. (Edit on the port seals it won't work but it will work fine on the China walls).
Even the Permatex product The Right Stuff is not recommended for sealing manifolds because of Gasoline and gas vapors. That product is outstanding for sealing oils.
Great idea on using a stud, could be an easy cure.

buns

Permatex #85420.




.

Westlotorn

That looks like a product to test, have not seen it before. Says it is a Polyester not a Silicone product. Re useable, wow. Anyone using this product?

SWCDuke

After spending thousands of miles on race tracks at 5-7000 revs from the sixties to the nineties, and countless road trips on two lane twisty roads in both cars and liter-plus sport bikes, I got it all out of my system.

Around most towns, today, there are few opportunities to open it up, and about all you can do is keep up with traffic, which could be done with a lawnmower engine. There's no need to drive a big V-8 even with a big cam around in second gear all the time if it's properly setup.

I recall driving your car (and recording the spark advance map and setting up the idle speed/mixture) and even that 30-30 cam pulled smoothly from 1000 revs and with the 3.70 axle top gear is good down to about 20 MPH.

I also remember you driving down Seal Beach Blvd., which has a 50 MPH speed limit and you never shifted out of third gear. I think you said you liked the sound of the side pipes.

I was always frustrated with with my Cosworth Vega and MBZ 190E 2.6 because on both cars fifth gear wasn't usable below about 45 MPH. I took me decades on each but I finally was able to retune those engines to have usable low end torque down to about 1500 or less. It took reindexing the cams on the CV along with an aggressive spark advance map, and after I figured out how to obtain a more aggressive spark advance map on the Merc by changing a resistor that was plugged into a socket on a wiring harness that was hidden by a wrap of electrical tape, I finally got it dialed in.

Now I can put both in fifth at 30-35 MPH and they will easily pull if I need to accelerate to keep up with traffic. Typical around town fuel economy increased by nearly 20 percent on both, but highway is about the same.

There's an old adage among engineers: People buy power, but they like torque. Count me in!

Dave - I recall you are running full time vacuum advance with a B26 VAC, which really helps with low speed fuel economy, but the CR is so high that you had to back the total WOT advance well below the optimum 36-40 degrees, and that is costing fuel economy.

Beyond that about all you can do is drive it in as high a gear as possible when your slogging around town in traffic.

As far as the oil consumption is concerned, the inlet manifold gasket seal is a likely suspect. Try leaning out the mixture to the point where it's running a little rough and loses about 100 revs, then move an unlit propane torque around the head/manifold interface. If the the engine smooths out/speeds up, you've found a leak, but it's a little tougher to isolate a leak on the valley side.

Flexible tube borescopes cost less than a hundred bucks, nowadays, and one could probably be used to snake down the ports and look for an oil film by removing at least the center carb, and even easier by removing all three.

Joe Lucia on the NCRS TDB can tell you all about big block gaskets. If you have to pull the heads you have a good opportunity to measure the CR and lower it. John McRae over on the TDB did that to a SHP big block to get rid of detonation. I recall he used a gasket that was well over .050" thick and it solved the problem, but head milling/block decking, and thick gaskets can knock the head-inlet manifold interface out of alignment and cause leaks.

Duke

Dave Cunningham

Everything is completely stock, L71 stuff, rectangle port 858 heads, with stock aluminum tripower manifold.