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I'm planning on doing my first engine swap in the next couple of weeks and want to get some advice/info on the used Pontiac 350 engine. It came out of a 1974 Lemans. The PO said it was a running/functional/unmolested engine that has never been cracked open before. I am swapping it into a 1977 Grand Lemans that has a 301 in it. The 301 has blow-by and leaks oil/coolant all over the place and I'm hoping to get it running before winter sets in. The questions i've run into already are:

1) What is your "go to" replacement routine in terms of seals/hoses/sensors when buying a used engine? Is it best to just throw it in and if something is messed up, fix it after installation? Some guy was telling me to replace the head gasket, oil pan gasket, and front and rear seals? Everything that didn't come with the engine I am hoping to get from the 301.

2) Will my distributor from my 301 work on the 350? I was told by the PO to get a new electrical one but a quick google search led to a black hole of options... May just be easier to use the 301's?

3) In image one, it looks like some plastic sensor/port snapped off the top of the engine. Comparing it to the 301, I'm not a 100% what it is?

4) In image two, there's a hole in the 350 on the top of the engine that is not on the 301. I was hoping to use the 301 for any routing/connection guidance but it seems like alot of **** is different (Vac lines, maybe for emissions?). Any ideas what goes here?

5) In image three, looks like some weird gasket goo was used for this piece on top of the engine. This area looks different than the 301 and maybe I need to replace it with the correct gasket?

Thanks again for any tips/tricks/information. This is my first engine swap and my end goal is just to learn how to do it. I know this isn't going to be a big racing machine, but it'll be nice to not be intimidated by engine swaps anymore.

If I posted wrong or did something I shouldn't, please inform me and I'll delete this post.


8,211 Posts
#1 look it over. I would check for any freeze plug that looks rusty enough to leak, or has an obvious trail from a leak.

Don't worry about the seals. The rear main is a rope seal, and unless it is real wet back there, chances are its holding fine. They are a pain to change.

I like to turn the engine by hand to feel if there is slack in the timing chain and I also turn them over by hand to listen to each cylinder as the piston is rising . as each piston is rising ,you will be able to hear air bypassing the rings. Also as the piston rises and the air is compressed the engine will provide resistance to turning. both of these can be checked to give an idea if an engine has a weak cylinder. If they all seem about the same and you get a pretty good resistance to turning the engine over as the piston rises, you should be good to go. You will hear the air escaping past the rings (slowly) as you perform these tests by hand.

Also a quick presumptive check for timing chain slack is a good idea.

Turn the engine forward to TDC. With the distributor installed ,and the cap removed, watch the rotor. Turn the engine over Backwards slowly and watch for the rotor to turn. If the crank can be turned farther than 12 degrees before the rotor begins to move, then the timing chain is loose.
They are easy to change , even in the car. so if you aren't sure, just move on for now.

Image #3 is the choke heater tube. Don't mess with it.leave it alone for the time being. It does have one tube that is broke and stuck in it, but it doesn't hurt anything.IIRC your 77 will have an electric chke so don't fool with it unless you like exhaust leaks.
Also in image #3 is a home made plate to block the EGR valve passage ways.Also a good place for an exhaust leak.Leave it alone for now.Concentrate on getting the motor ready to install .

Image #2 is the place that a PCV valve slips into.You still have the grommet intact, so just shove a valve in it.You may have to lengthen the hose to get to the place where it connects on the carb. Small potatoes.
You could pull the intake manifold and use the 301 valley pan, but I wouldn't. Note the 301 intake will not fit this engine, so don't even try to swap it.

Image #1 is a vacuum switch. It is operated by hot water. when the water heats it switches the applied vacuum from one to the other port openings .

They are used for several different things, like switching the vacuum source to the distributor advance from manifold to ported as part of a warmup strategy for emissions. I would have to reference a chart to tell you exactly what that one does. For now lets move on.

Pretty much just do a visual check for any obvious signs of leakage and install the thing.
Be sure the flex plate is correct. ( Big starter gear thing on back of motor)
Make sure the gear is good and has all its teeth.
Use the one supplied with the engine , not the 301 plate. There are differences and it may cause a vibration problem .
Be sure you have the correct motor mounts as well. You will see there are 5 possible places to bolt them on also ,on the 74 block.(That is a good thing)
as some of the early engine were missing a few LOL

Its nice that you have a 4 barrel intake.thats a plus.

NOW.That all being said do one last check. Back on the engine behind the passenger side cylinder head, is a cast in number, like say 500577 or maybe 500810. This will tell you what engine You have.Look for it and post the number. Here is a link to read about it.

How to identify your Pontiac engine

You may have a 400. :cool: You should check.
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