Hi all,

New here and hoping I could get some help replacing the intake and headgaskets on my 350. The motor is a recent replacement from the 307 smogger in my 86 Parisienne. I believe the motor is an 83? Thought it was older but when I replaced the oil filter it turned out to be the same size as my 307, not the older large size. I'll see if I can confirm the block #.

Anyways, I noticed a sweet smell out of the tailpipe along with dropping coolant and oil levels. Oil did not seem milky when I changed it. Nothing dripping under the car. So my guess is intake gasket, headgasket, valve seal leaks or a combo of all. I want to do them all myself and geth
get the rocket running clean and hope some of you guys could offer some guidance, since Ive never pulled apart a top end like this.

My first question.

How do I identify my heads?

Leo

 

All SBO heads are identified by a number cast into the cylinder head by the #1 plug. If they are SBO 350 heads I think there is only head gasket design. If you had the original steel shim (thin head gasket) you will want to avoid Felpro as their gasket is .040 compressed. There are gaskets available that are around .028 compressed, if you trying to keep your compression "up".

 

Confirmed 3A heads
I'm not sure if the stock metal gasket is installed, it looks like there's a noticeable gap between block and head. The intake is a edelbrock performer 350 and silicone is bubbling out of the front and back. This was definately taken apart, and I can see some coolant near the front of the intake where the silicone is.
If the heads have been milled before or if I mill them when I pull them off, will I need to find a specific intake gasket?
I have heard both ends of the silicone argument for intake manifolds, any thoughts?

 

3A heads mean is is a 77-80 olds 350. They did not use a shim gasket. If it has a Performer intake on it, it obviously had been changed as that is not stock. Changing the intake gasket is a "medium" job, head gaskets are a big deal. Plus, they really don't leak very often. I would investigate further, and if you need to replace in intake gasket, use the My Gasket Ultra-Seals. I bet it has the stock turkey tray (which I have used with no problem on Edelbrock intakes).

 

Do a compression test. If your compression is good, then you are not likely to need a head gasket.

- Eric

 

Use the turkey tray, very easy to install. I could not even get the bolts installed in my Performer intake with Ultra seal intake gaskets, bone stock 76 350.The composite gaskets are thicker and many have found warped flanges on Edelbrock manifolds. Put RTV around both sides of the gaskets on the 4 corner coolant openings and a good, thick bead on both end rails. I also use Permatex Aviation sealant around both sides on the turkey tray around the intake ports

 

I myself had a bit of a deal with my turkey tray on my 76 had to test fit it several times to get the tabs to go properly prior to RTV . As olds 307 and 403 says its not as bad as it sounds.

 

Thanks for the replies. I nervously did a compression test today (removed all plugs, fuel line and ignition wire. Cranked 4 revolutions and recorded final compression. I did not depress the throttle.) and found these results:
Cylinders 1, 3, 5, 7 all meet at 100.
Cylinders 2, 6, 8 were at 95 while cylinder 4 seemed to have great compression, jumping to 100 no problem.
I went back to the #2 cylinder (seemed to have the worst compression) and dripped a bit of oil in and did the compression test again, it didnt have any effect on the compression which makes me think that my rings are ok.

Is there a way to post pictures? I took a few and it really helps describe the situation.

Anyways the plugs all looked the same, there was a bit of oil on a few around the seal but no sign of coolant that I could notice. This was after I ran it this morning, and I havent noticed much smell or any smoke today, however my coolant level continues to drop.

I am noticing small coolant leaks around the intake seal, but nothing hitting the ground.

Anything else I can do to rule out head gaskets? I would rather not replace the intake seal if the head gaskets need to be done a short while down the road.

 

I have heard the turkey tray is not a good one to use for the aftermarket intakes. Not sure if that is true but throwing itr out there from what i heard

 

95-100psi is definitely consistent with a smog motor with a thick head gasket, and is a completely reasonable range.

It sounds like your head gaskets are good.

Also, if your burning coolant, that plug will look unusually clean.

- Eric

 

Have you pressure checked the cooling system and checked for external leaks?

 

The plugs looked dry, none of them looked unusually clean or wet at all. I'll pressure check the system, but I already know of a couple leaks around the exterior intake seals, so I'll be replacing the intake gasket anyways. I'll check out what's under the manifold and make my determination from what I see. The turkey tray sounds good if it will work, but I think I might want to go with a thicker gasket against the ports instead of the thin shim I see. And RTV should take care of the rest I assume.

 

Never had an issue with the turkey tray on multiple engines with aluminum intakes. Hopefully your Performer is straight. I had no issues with SCE composite gaskets other than the gasket moving on my 403 with a RPM intake. I would let the RTV cure on the head side with composites before putting on the intake

 

If it ain't broke, don't fix it
Always look first at the last item "fixed" for the trouble.

You know the intake is leaking coolant at the head, if I am not mistaken. That's probably all you need to fix.

I think RTV silicone is the wrong thing to use on the intake to head except perhaps at the water seal areas on the corners, and then only just enough to effect a seal. I have seen many an engine and radiator with strings of RTV blocking cooling passages after they broke away from where too much was applied. I feel that other substances are better at permanently sealing the intake fuel/air ports, e.g. Permatex 3H Aviation sealer.

For the end rails, sure, lay down a fat bead of silicone just before the final install of the intake. It won't get pinched so far that it will lead to breakaways inside.

TEST FIT DRY again and again until you are sure the install will go smoothly, THEN apply your sealers. Have ALL the bolts cleaned and oiled and ready to go, and the torque sequence posted nearby, or memorized. I like to go in 2-3 steps- real light, snug, then with torque wrench to the prescribed figure, then again until all fasteners click the torque tool before turning.

 

Your compression looks fine, all cylinders within 10%, I'd just change the intake gaskets with whatever gaskets your engine calls for, don't try and out think GM and no matter what stop stiffing the tailpipe in your driveway or the neighbors might call the fuzz.

 

The same GM that states that .0007 is adequate main bearing to crank clearance???

Normally I agree, but keep in mind he is NOT using the factory intake. That said, I also have used the turkey tray with aftermarket intakes with no issues. I also have had good luck with the brush on aviation sealer that the others mentioned.

 

"I did a compression test today... Cranked 4 revolutions and recorded final compression. I did not depress the throttle. "
=========================

Probably not the best method to fill the cylinders with air. The throttle is supposed to be propped open.

 

Damn, I missed that. Serves me right for reading posts on my phone.

That test is completely invalid.

- Eric

 

I wondered why the directions called for throttle, I assumed it was for a fuel injected system. I couldnt locate a fuel pump fuse to pop out and I didnt want gas spraying everywhere so I just removed the gas line to the carb. I suppose I will re-test tomorrow and see what readings I get when I depress the throttle.

 

You have a mechanical fuel pump, no worries about a fuse.

 

Gas won't spray everywhere. Where would it spray from? There's no need to disconnect the fuel line.
No need to remove the ignition wire either.

And you can go more than 4 revolutions - you want to go until the gauge reading stabilizes, which is probably 5-6 revolutions.

- Eric

 

Would there be any difference in max compression with wide open throttle versus no throttle? Or would it just take longer to achieve max compression..

 

Numbers should be higher, it is difficult to compress the air if there isn't any to compress.

 

Ah. Now you're invoking the Universal Gas Law.

Yes, in theory, if you crank long enough with the throttle plates closed, you will draw enough air in through the idle jets that you will reach peak pressure, but that assumes that you are not losing pressure through the ring gaps with every cycle, which you are, and this loss could reach a stasis point in terms of how much can be drawn in through a small space, and give you an inaccurate reading.

Throttle plates must always be fully open when checking compression.

- Eric

 

I zip tie my throttle wide open and put a big screw driver in to prop the air door open. Simply unhooked the big red power to the HEI and you are golden. Make sure your motor is warm too.

 

Just finished retesting compression with the engine hot, wide open throttle. Measuring the max recorded compression after turnover I found the following:
Cylinders 1, 3, 5, 7 were all within 3 degrees with 99, 98, 97, 100 respectively.
Then my battery started to get weak as I went counter-clockwise around the engine.
Cylinder 8 measured 99.
Cylinder 6 measured 94.
Cylinder 4 measured 92.
Cylinder 2 measured 80.
By cylinder 2 the starter was barely turning over, I would think that this caused the lower compression reading. Especially since I didnt read anything below 95 on that side of the engine when I tested yesterday with the engine warm and closed throttle.

Side by side numbers for that head, yesterdays numbers with closed throttle and todays numbers with WOT and low battery:
8 - 95 - 99
6 - 95 - 94
4 - 100 - 92
2 - 95 - 80

The engine may have been a bit warmer today as I tested immediately after warm up, but it was warm yesterday, tested after maybe a half hour after a good ride.

 

I love to pick nits, so:
6 revolutions is three compression strokes...

 

Curse you, you fiend!!


And, Fox, charge your battery and repeat the last two or three.
If the starter was going as slowly as you say, those numbers look good.

Also, get a new battery - that one's shot.

- Eric

 

I checked out what kind of gaskets autozone had today, none had the turkey tray that I would like to get. But he did have a Fel Pro set that was composite, I think that's what I will go with and add a turkey tray if it will fit with the aftermarket performer 350.
And I should toss the front and rear seals provided and use just Permatex? Sounds like aviation sealer is the best recommendation, didnt see any at the parts store. There's so many RTV sealers I wouldn't know which to choose from.

 

Yes, throw out the front and rear rubber seals and use RTV.

Everyone will have a different opinion, but I have used high-temp black RTV for the gaskets with no problems. It's what's included in the box with the Fel-Pros.

- Eric

 

X2 no need for rubbers.

 

Thanks for all the help guys. I installed a new turkey tray and noticed that the old one had been installed incorrectly. All 4 tabs were squashed as if they were never lined up. Seems to be holding together well.

My only remaining concern is if I missed a corner of one of the rails with RTV, would I see any oil or lose oil pressure?

 

You wouldn't lose any pressure, but you'd begin to see some oil oozing after a while.

- Eric