Ok so this is my first post but I have been reading everything I can.Here's my problem.I recently blew a head gasket on my 87 Regal w/307 v8.I got everything together and I am having problems getting it to run.I pulled the carb. off and took it to get rebuilt.That's when I found out that I have a 1985 Oldsmobile 307 in the car. Now my problem is,I asked for a head gasket kit for 87 307.Now naturally 87's had 7a roller heads.So now I am faced with a 307 with 5a non-roller head's. Now this is what the car is doing.It won't start unless I treat it like it's flooded.Foot to floor and hold the key until she runs.Then it won't idle.I can hold the engine to 1,000 rpm's and it will run for short periods.It doesn't run very good/at all at anything above 2,500 rpm's.I am thinking that maybe the 7a intake manifold gasket is impeading the flow of the 5a heads. please someone help me.........thanx in advance Richard
I've got this feeling you have a really bad intake leak. It sounds like the intake has to come back off and the correct gasket installed. The 7a heads had small intake ports so the gasket mismatch could be a big part of the problem. Good Luck Tom
The head gaskets should be the same--just the intake runners were diff. like tom said..If your afrad of the geadgaskets being wrong just give it a compression test and you'll know forsure---Sounds like a bad vacuum leak to me Brian
thanx guys you pretty much confirmed my fears.I already checked and the head gasket's should be the same and are probly fine.I am certain I don't have a roller motor in the car.It could be a good thing,5a=better flowing than 7a's.I just wish I would have known before I put it back together.Oh well at least it's just 12 bolts and the intake comes off.I will probly start on it again tonight.I had to take a day away from it so my back could recover,lol. thanx again.
Hang on a second, are you SURE about the year on the engine? If it's really an 85 motor, it should also have 7A heads with the smaller intake ports, UNLESS it came from a 442 with the Vin "9" engine. All 307s with the exception of the vin 9 "HO" motor switched to the 7A heads and roller block for the 1985 MY. The vin 9 "HO" engine switched for the 1986 MY. If you've decoded it as an actual 1985 MY engine, you might have the slightly better HO camshaft in it. Also, I've used intake gaskets for earlier model Olds V8s on a 7A headed 307 and didn't have an intake leak. I usually use the Mr. Gasket 405G fiber gaskets and trim the factory intake gasket down to just the turkey tray.
The head number and block numbers on small block Oldsmobile engines are easy to spot. The head number is located in the lower left hand corner of the heads. The block number will be on the flat area behind the water pump to the right of the oil fill tube. Engines with 5A heads will have the cast iron exhaust manifolds and the 7A heads with have stainless steel exhaust manifolds. The differences in sizes of the exhaust ports are incredible with the 7A being half the hieght. Since the Rochester Quadajet are the same for a number of years the carb may have been swapped at an earlier date. Hope this information helps
Plus, from my experience, a 7A headed engine will run just fine with the earlier carb. However, the 5A headed engines don't much care for the later carb and tend to run lean with it. Later carbs have an integral rich stop while the earlier ones have separately adjustable rich and lean stops. It might be possible to calibrate the later carb to run on the earlier motor but I've never tried.
