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post #1 of 8 (permalink) Old 03-31-2019, 11:18 AM Thread Starter
 
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72 pontiac 350 improvement suggestions

Hi,
I have a 72 Lemans convertible with a 350 2 bbl auto with about 75K on the car. Have to go into the engine as every seal is leaking.

Any suggestions on changes that will improve fuel economy or driveability? It is a 49 state vehicle. Not looking to do a major overhaul, but thinking camshaft, carbs, electronic ignition, emission stuff that can be disabled, etc.

Any stuff that I should do while I have the engine out?

Thanks!
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post #2 of 8 (permalink) Old 03-31-2019, 04:15 PM
 
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Originally Posted by oskarm View Post
Hi,
I have a 72 Lemans convertible with a 350 2 bbl auto with about 75K on the car. Have to go into the engine as every seal is leaking.

Any suggestions on changes that will improve fuel economy or driveability? It is a 49 state vehicle. Not looking to do a major overhaul, but thinking camshaft, carbs, electronic ignition, emission stuff that can be disabled, etc.

Any stuff that I should do while I have the engine out?

Thanks!
Hmmmm, every seal is leaking and you are going to have to totally disassemble the engine, yet not rebuild it. Hmmmm, not making sense to me. Have you done a compression test to see if the engine is low on compression and will need rings?

If you just reseal it, I assume not including the head gaskets and you are leaving the heads in place. Is the rear main seal leaking?

If you pull the engine, you might want to take the car to a muffler shop and let then heat up and loosen your exhaust pipes to make it easier for you. If you don't already have dual exhaust, you want to add this to aid in engine performance and can add a little gas mileage.

When you replace the pan gasket, clean out the pan and install a new oil pump/screen - that's a no brainer. Install a new aftermarket hardened steel oil pump drive to go with it.

With engine out, replace all freeze plugs on the block.

1972 350 2 bbl is rated at 175HP and 8.0 compression. You can go with a Competition Cams grind having 110 LSA to boost cylinder pressure, but in doing that, if your rings are worn, you could wind up with excess blow-by or burn oil. Get matching springs to go with the cam but keep lift under about .450". Install new valve seals, but if the valve guides are worn, the higher lift/heavier springs may accelerate it more and you will be burning oil.

Install a new timing chain & gears.

Swap out to a 1972 factory Q-jet intake with Q-jet carb. This will help with fuel mileage running on the smaller primaries and give you an extra kick with the larger secondaries. You don't get fuel mileage from these older cars as you do the newer cars. If you can get 18 on the highway at steady speeds and flat roads, you will be doing good. Open element air cleaners can help a little with this and then dialing in your timing can maximize gas mileage. If an automatic trans, an RV converter with less stall can improve gas mileage as does a shift improver kit to give you fast/crisp shifts of the gears.

Electronic ignition is a personal preference. Points work fine, but todays Chinese stuff can be a problem. I have used the Pertronix conversion for points and had no issues. You can use a factory or after market HEI which many like. Then there are complete aftermarket plug-and-play electronic small cap distributors.

Don't know what emissions crap you have on the engine, so can't help you on that.

So that is for starters.
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post #3 of 8 (permalink) Old 04-01-2019, 06:15 PM Thread Starter
 
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Thanks

Compression is good. Front, rear mains leaking. timing cover is leaking. Pan under intake is leaking, oil pan is leaking.

Basically the car was driven for about 300 miles every 2-3 years for the last 6 years or so, so not enough to keep the seals lubed up. Was going to try and replace the rear main without taking out the crank. I see there are some aftermarket alternatives instead of putting in another rope seal. Never been a fan of rope seals if you don't plan on driving often, however the materials today may be better than the 60's-70's stuff. Didn't plan to pull the heads or the exhaust manifold.

Just trying to figure out what changed 70-72 engine wise. 71 HP was less than 70, 72 was less than 71. figured most of it was probably cam, carb, and emissions stuff. They use to detune and depower to meet emissions back then.
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post #4 of 8 (permalink) Old 04-01-2019, 08:24 PM
 
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"...what changed 70-72 engine wise..."


Compression was decreased in all Pontiac engines, after '70. Most Pontiac engines were reduced even lower, to 7.6, later in the '70's.

In '72 they began using some sort of "net" hp rating, which meant that a '72 engine which was almost identical to a '71 engine would have a lower hp rating.

https://www.hagerty.com/articles-vid.../13/horsepower

http://www.city-data.com/forum/autom...gross-net.html

Use this link to check the difference between a '71 & '72 350.

http://www.wallaceracing.com/enginesearch4.htm

Last edited by bigD; 04-01-2019 at 08:46 PM.
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post #5 of 8 (permalink) Old 04-02-2019, 06:02 PM
 
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bigD is correct on the HP change - a compression drop and how HP/Torque was rated. I posted this somewhere before. 1971 was a change over where engine HP ratings went from HP at the flywheel without accessories to net HP with all the accessories like PS, AC, Alt, exhaust system, etc..

Ok on the re-seal. I did this once on a 350CI I had in a '67 Firebird as it was an oil leaker. Pulled the engine and installed new gaskets and problem solved. I cannot recall if I replaced the rear main, but I don't think so.

Again, I would not mess with the cam/lifters and leave things alone for the reasons stated. I would however install the new timing chain & gears and oil pump/pick-up/oil pump shaft.

You will also be installing a new timing cover seal. Look at the harmonic balancer snout. Old seals will dry up and then cut a light groove into the balancer snout. They make a repair sleeve that can be inserted onto the end of the balancer to provide a new surface IF you re-use it and it has a groove. I have used these and never had any problems. Did a web search and found this at Summit. Some versions seem to have a flange and a "cup" tool to help installation, I used this type and you have to be careful when tapping it on, it is by Mahle and the only one I could find. Here is Summit's version. https://www.summitracing.com/parts/m...SABEgJmYfD_BwE

I did find a sleeve at Advance Auto that has what appears to be the "cup" to help knock the sleeve into place. It is by National, Part No. 88186 https://shop.advanceautoparts.com/fi...r-sleeve.c8019

HOWEVER, a better solution all around would be a new balancer. Many times, due to age, the rubber bonded area will be dry rotted or be cracked and can cause the outer inertia ring to slip or separate completely (worst case scenario). This is one of those items best replaced. You can get an aftermarket replacement for about $50 and it is insurance in my book. Example here - https://butlerperformance.com/i-2445...tegory:1234723

I use Summit on my parts because anything after a $99 order is free shipping unless otherwise noted. So you could work up a list of parts and make your order over $100 and save on shipping.

Last edited by PontiacJim; 04-03-2019 at 05:58 PM. Reason: Asleep at the wheel.
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post #6 of 8 (permalink) Old 04-03-2019, 03:00 PM
 
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PontiacJim,

Doesn't the timing cover seal rest on the balancer, and not the crank snout? I have a '69 400, I thought they were the same.


Joe
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post #7 of 8 (permalink) Old 04-03-2019, 05:16 PM
 
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PontiacJim,

Doesn't the timing cover seal rest on the balancer, and not the crank snout? I have a '69 400, I thought they were the same.


Joe
Yes! My bad. You are 100% correct. Edited my previous post to reflect this. The balancer slips on over the keyway on the crank, so the timing cover seal does indeed rest on the balancer.

Also went back and had to do some digging, but believe I came up with the correct repair sleeve - one has the flange and "cup" to make installation easier and one that does not which just takes a little more care to install (which I have used). So if anyone reads this post at a later date, the info should be correct.

Last edited by PontiacJim; 04-03-2019 at 06:01 PM.
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post #8 of 8 (permalink) Old 04-06-2019, 02:30 PM
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I have installed several BOP Viton Rear main seals on Pontiac 389's and 400's. Zero leaks after years of service and thousands of miles. Both one and two piece seals. You need to pull the engine and pull the main caps so that you can lift the crank an inch or so to install the seal. Well worth it. At this time, replace the core plugs and all other gaskets except the head gaskets if you aren't doing the heads. I performed this exact same operation on my '67 GTO 23 years after I had overhauled the engine. It was leaking oil out of every possible area. A new rear main, new gaskets and core plugs, and it's been bone dry since 2011. Driven thousands of miles since. Well worth the effort, and very easy to refresh the engine bay with the engine out. Pulling one of these engines takes me 45 minutes.
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, LeMans & GTO Engine Tuning and High Performance

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