70 L46 engine problem

[Mike T.]

Recently purchased a 70 L46, and got it started over the weekend.
Right exhaust is perfect, smooth and clean.
Left side has much higher exhaust pressure, runs too rich, and blows oil when warmed up.
I manually kept heat riser open, and it didn't make a difference in pressure.
Step one is to run a compression check, and then do valve guide seals on left side.
Any other ideas?
THANKS!

[William C.]

Re: 70 L46 engine problem

I'd suggest starting with a leakdown test. I'm not too sure what you mean when you say "higher exhaust pressure" and "runs too rich" on one side only, the intake manifold and carburetor are generally relatively indescrimanite disbursers of the fuel/air mix.

[Mike T.]

Re: 70 L46 engine problem

I know this is really weird. There is tons of air coming out the left side, and it smells too rich.
The right exhaust tip is clean, and has about half as much air volume coming out.
I talked to the seller again today, and he confirmed that the car ran absolutely perfect when he last drove it.
I have a theory. He stopped driving it because the flywheel ring gear stripped. It also had water in the gas tank, that was caused by a bad seal betwee the filler neck and the tank.
Before I started it, I cleaned the tank, gas lines and replaced the fuel pump. I had the carb rebulit by a professional, who bead blasted the bowl because it has corrosion.
With the carb off, I saw some evidence of rust in the intake manifold. I wonder if the water in the gas was allowed to lay in the intake manifold and in the combustion chamber for an extended period of time, and it rusted/damaged the rings and/or cylinders.
Looking inside of the intake, the left side is lower than the right side, so this would give more credibility to the theory that the water ran to the lowest point, and caused engine damage to the left side.
Do you think I'm on the right track?
I'm gonna do a compression check, but that wouldn't indicate the condition of the oil rings, would it?
Thanks for your help Bill.

[Kurt G.]

Re: 70 L46 engine problem

The compression check will give you an indication of a ring problem. I'm no engine genious, but the compression test will tell you of any type of blow-by problem, whether it's rings or valves. The problem you're going to have is determining which it is, rings or valves. You mentioned valve guide seals. Is the car only smoking after start up? That little blue puff of smoke when starting is usually caused by bad guide seals. If your engine is smoking almost all the time, then you have other issues, probably rings.

If you have access to a borescope, I'd suggest you go thru the plug holes of the left head to take a sneak peek at the tops of the pistons and the cylinder walls, or you could do it the old fashion way and just pull the head. Either way, you are looking at the potential of a lot of work. I'll keep my fingers crossed for you that it's only a little puff of blue.

Oh, by the way, did the previous owner tell you when it ran perfectly last. I'm guessing several years ago maybe?

[Mike T.]

Re: 70 L46 engine problem

Thanks for the reply Kurt.
He drove it with the water in the gas, and then it sat for about a year and a half. He didn't start it because of the bad ring gear on the flywheel.
It smokes on startup, and then doesn't smoke until it gets warm after a few minutes. When it's warm, and I run it at higher RPM's, it smokes a lot.
I've put Marvel Mystery oil in the oil and the gas, hoping it would free up a ring or a valve. No luck yet.
I just have a feeling that the much higher exhaust pressure on the left side is related. to the problem.
I didn't mention this earlier, but the PCV on the left side kept popping out of the rubber grommet. I thought that the grommet was worn. It's not as bad now after I have run it several times. Maybe it's not the grommet, and it's related to too much crankcase pressure due to blowby.

[Edward J.]

Re: 70 L46 engine problem

Mike, really never heard of exhaust flowing out more on one side than the other , with the exception of when the heat riser is shut on cold start, is it possiable that one muffler is different that the other, or one baffle is missing in one of the mufflers.

The oil burning may just be valve seals as it is the most common problem with small blocks and big blocks , and have I seen where the two center bolts on the intake on left and right sides will push oil up the threads of bolts and the oil will make its way into the intake manifold runners causing smoke after the cars been running for about 30-45 seconds after start. this is a hard problem to detect, but if the intake gaskets have been in place for awhile they maybe compressed and this is how the oil makes it way to the intake runner.chevrolet had a service bulliten in the mid 80's on this problem. if you see oil puddling on the top of intake around those center bolts left or right , crankcase pressure will push the oil upwards around the threads of those bolts.

[Joe C.]

Re: 70 L46 engine problem

I agree with Ed on the muffler and/or heat riser theory.

FYI: A dual plane intake, such as the one installed on your engine has intake runners/plenum/ main jet config as follows:

Driver's (left or low) side venturies/main jets/plenum half feeds cylinders 1-4-6-7.
Passenger's (right or high) side venturies/main jets/plenum half feeds cylinders 2-3-5-8.

Inefficiencies in dual plane manifolds sometimes cause mixture imbalance which is not dependent on BANK, but on the above groupings. Dual plane manifolds, despite this fact, provide better drivabiliy at low/midrange than single plane intakes. Stagger jetting is used in extreme cases, but is very often not necessary, even with dual plane intake manifolds.

If you have not already installed a fresh set of R45 plugs, then it would be a good idea to do so at this time.

[Patrick H.]

Re: 70 L46 engine problem

Mike, really never heard of exhaust flowing out more on one side than the other , with the exception of when the heat riser is shut on cold start, is it possiable that one muffler is different that the other, or one baffle is missing in one of the mufflers.

The oil burning may just be valve seals as it is the most common problem with small blocks and big blocks , and have I seen where the two center bolts on the intake on left and right sides will push oil up the threads of bolts and the oil will make its way into the intake manifold runners causing smoke after the cars been running for about 30-45 seconds after start. this is a hard problem to detect, but if the intake gaskets have been in place for awhile they maybe compressed and this is how the oil makes it way to the intake runner.chevrolet had a service bulliten in the mid 80's on this problem. if you see oil puddling on the top of intake around those center bolts left or right , crankcase pressure will push the oil upwards around the threads of those bolts.

Ed,

Do you have a copy of that service bulletin?

Patrick

[Paul J.]

Re: 70 L46 engine problem

Mike:

The wife's Bridge club is here and I've had too much to drink (not because of any enjoyment on my part, I think I just saw Bea Arthur!, HELP!).

Joe and Ed are giving you some good advice, but your air flow observation is puzzeling. If you have a bunch of time to waste you might want to pull the muffler on the right side and run a snake up to the exhaust manifold. If there is an obstruction it may be from mice. Also beat the muffler to loosen any thing in it.

This is uncommon but you said the car sat a while. My guess is Joe and Ed are on top of it, but WTFDIK, where's the bourbon?

Paul

[Edward J.]

Re: 70 L46 engine problem

Ed,

Do you have a copy of that service bulletin?

Patrick

Patrick, I don't have a copy of the bulletin , I use to have a box of old Chevrolet TSB'S, one my wife was doing a cellar cleaning one year and decided to throw out all my old magazines, all my training materails and TSB I had collected for years.

I can tell you that it was a common problem with GM small blocks, the heat cross over did a number on the gasket and when the bolts loose there torque engine oil would be drawn into the intake,the end result was using oil smoke on start-up. those center bolts on the intake are tapped through into the engine block crank case pressure cause the oil to travel up the bolts, thats why those bolts use a sealer.

[Patrick H.]

Re: 70 L46 engine problem

Patrick, I don't have a copy of the bulletin , I use to have a box of old Chevrolet TSB'S, one my wife was doing a cellar cleaning one year and decided to throw out all my old magazines, all my training materails and TSB I had collected for years.

I can tell you that it was a common problem with GM small blocks, the heat cross over did a number on the gasket and when the bolts loose there torque engine oil would be drawn into the intake,the end result was using oil smoke on start-up. those center bolts on the intake are tapped through into the engine block crank case pressure cause the oil to travel up the bolts, thats why those bolts use a sealer.

Ed,

Do you recall if GM had anything particular for a fix other than replacing the gaskets and using new sealer on the bolts?

Patrick

[Edward J.]

Re: 70 L46 engine problem

Pat, GM pipe thread sealant, but the threaded hole needed to be clean, no oil, I can tell you that the non harding permatex sealant works to( brown colored and in a small bottle with a small applacator brush affixed to the cap). Most auto parts stores carry.

[Craig B.]

Re: 70 L46 engine problem

If your old sparkplugs look the same 1-8 then I would say your oil burning problem is common to all cylinders. The backpressure apparent on the left exhaust maybe explained by the car sitting for a year and a half and a rodient finding your exhaust to be an ideal home or a young child finding your exhaust an ideal receptacle for their ball.

[Paul J.]

Re: 70 L46 engine problem

If your old sparkplugs look the same 1-8 then I would say your oil burning problem is common to all cylinders. The backpressure apparent on the left exhaust maybe explained by the car sitting for a year and a half and a rodient finding your exhaust to be an ideal home or a young child finding your exhaust an ideal receptacle for their ball.

Right side, Craig. Read posts #3 and #9.

[Mike T.]

Re: 70 L46 engine problem

Got a confession to make. I said I did a compression check, but I only did it for the left side. That was the only side that was a problem. It had the high exhaust pressure, and was burning oil. The right side exhaust was low pressure, very smooth, no oil burning, and no miss was detected.
I have since done a vacuum test, and it violently fluctuated between 0 and 22 lbs. Everyone told me that a valve must be stuck. Sure enough, I took the right valve cover off and the #6 intake valve was stuck open. The rocker had even slid off of the valve. The valve was stuck solid.
My mechanic buddy suggested filling the intake full of a 50/50 mix of Marvel Mystery Oil and Berryman's B12 and let it soak for a week. I did that, but the valve was still stuck. Over the subsequent week, I took the spring and retainer off the valve, so that I could spray some PB Blaster on the valve stem and guide. I tapped carefully on the top of the valve with a small hammer. No luck after several days. I eventually noticed some orange liquid squirting out of the valve guide as I tapped on it. I suspect this was rust, that the PB Blaster was working on in the valve guide. Long story short, I finally got the valve to move and I am in the process of reassembly.
I think my theory is going to prove right. The previous owner ran it with water in the gas. He shut it off and left it for over a year. The left side of the intake showed some rust in the inside. The #6 intake valve that was stuck is fed from a runner on the left side of the intake, so the water laid in the #6 hole and rusted the valve stem to the valve guide.
I wish I had soaked the motor with the 50/50 Marvel Mystery Oil and Berryman's B12 before I tried to start it. I hope there wasn't rust in the cylinders that damaged the rings. Time will tell I guess.
Thanks for all the help guys! I'll keep you posted.