Find answers to Frequently Asked Questions for First Generation Firebirds that have been asked and answered on FGF. Special thanks needs to be given to all the FGF members who took the time to respond to other member's questions.
Engine - OHC Specific
Reference:
- 1968 Dealer Service Information Bulletin 68-I-68
- 1967 Dealer Technical Bulletin 67-T-13
Q: OHC Meaning
I keep reading OHC for engine descriptions. What does this mean?
A: OHC – Over Head Cam which correlated with the 6-cylinder.
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Content last modified: January 16, 2014 at 2:55 pm
Q: OHC-6 Buildup
I am starting to get ready to rebuild my “rebuilt” (so said the previous owner) OHC-6. I know some of the problems these engines have with oil and wiping out camshafts, but I was wondering while I have the block torn apart, are there any special machining operations I should have done? I am concerned about the cam bearings, since I have already lost a few 1-bbl cams (or actually have housings from wiped out cams).
The combination that I am planning on running is:
– 1968 1-bbl head (9.5:1 Compression ratio) fully machined with new valves and springs (single)
– 196? Block (I plan on putting in new bearings and rings, pistons if needed)
– 1968 Sprint Cam (found NOS from Internet… long story)
I plan on getting new oil pump gears and a new timing belt as well. With a lot of money involved in this engine, I would like to make sure it will last. I am planning on pulling the engine out in the next few weeks, and would like to be finished for next spring. I have put 25 miles on the car this year, due to moving and other projects (1968 Catalina).
I also have two other questions:
Where did you get your exhaust made? Do they have a pattern for it? I have asked several “custom” exhaust shops about doing this and they have all said it cannot be done. I saw it done on the Fitchbird, and personally I want the splitter exhaust tips.
AC was not available on the Sprint? Why was this? My car is originally a 1-bbl, but came with AC. I am making this into my dream Sprint (does this answer your question on options?), and will keep my AC. I am just curious about not having it available and the why.
A: I ll try and answer a few questions on the OHC rebuild. A properly built motor will not wipe out cams. Especially with todays super lubricants. The cam housing is made of aluminum and has no replaceable bearings.
It is important to pay close attention to the upper oiling system as this is what I see screwed up the most. Next is to pay attention to the valve setup. DO NOT tip the valves. You will get interference between the follower and valve spring retainer. Lash adjusters will compensate for the change in stem height. I will say this again… get a factory service manual… In the case of the OHC-6 get a 67 manual as well as the year of car you have. The 1967 manual has more OHC-6 info than any other year.You will need the year of manual for your car because they made some changes over the 4 yrs of producing this engine.
If your year is 1967 (you didnt state) then you save money on manuals.67 Firebird Sprints were avaliable with factory a/c as was the Tempest /LeMans Sprint for 66-7. However in 68-9 it wasnt avaliable as an option for any Sprints. Reasons are not clear but I suspect the following: compressors were dying right and left on these engines (try and engage a a/c compressor clutch at 6500 rpm and see what it does.) sales of the a/c equipted Sprints were very low (i know of only a handful and 2 are here), Like the R/As Sprints were built for the hot rodder who didnt neccessarily want extra baggage.
You can successfully convert a 1bbl car to a Sprint and retain the a/c but there are some parts that are peculiar to the a/c equipted Sprints. As for the duals on a Sprint Glenn took a little different approach than i did. I personally think that his is too loud the way its done and he uses tailpipe extensions that protrude beyond the bumper to help with the cabin noise level. The approach I used for a dual conversion is this. Buy over the counter dual exhaust for the V-8. get the crossover muffler and the front resonators dont buy the front pipes for the V-8.
Use V-8 tailpipes(here comes the dual splitters you wanted) install all of this on the car with proper dual exhaust hangers drive it to a muffler shop that can custom bend pipe and have them make the front two pipes (maximum size of 1-7/8 in dia) to make up to the front resonators.this system is large enough for the Sprint but isnt terribly loud.
We have experimented with just resonators or just the cross flow muffler, and they are both too loud. You can subsitute small mufflers in place of the resonators if you want to further quiet down the system. If you are going to run single valve springs make sure they are to the same specs as the DUAL springs that the Sprint had. With the 1bbl head and valves you are pushing it as far as lift and coil bind on a 4bbl cam.
You didnt say what combo block ,crank and pistons you will use but its good to keep the CR just under 10:1 for the street. However if you increase the CR to 11:1 or higher it really wakes this motor up. I have tried about every combo of head ,cam,crank,pistons and find that the 68-9 4bbl head is best on the 230 If overbored.But a killer combo is the other way around and use a 66-7 4bbl head on a 68-9 short block. Hope this helps
A: Reagarding the exhaust, I had a friend who worked in a shop with a bender, and he still had the pattern cards for 1967, 1968, and 1969 Firebirds, we copied the factory axle tubes, but with 2-1/4″ pipe. We used resonators with 2-1/4″ inlets and outlets, same for the muffler and for the tailpipes. (Remember my muffler went away with the rear suspension mods.) We made 2 engine pipes from 2″ stock, the manifold outlet for cylinders 1-2-3 went to the left resonator, with most bends resembling the factory 1-barrel pipe, then the manifold outlet for 4-5-6 had the pipe make an S-turn under the transmission crossmember to connect to the right resonator. Both pipes needed to be enlarged at that point to fit into the 2-1/4″ resonator. It is not difficult for a pipe man with a BRAIN!
On the engine, there are NO cam bearings! The cam rides right on the surface of the housing, and I’ve never seen a housing wear out, even after 200,000 miles or more! You need to make sure the oil restrictor in the head is not damaged, so you get the right amount of oil pressure and volume to the top of the engine. Also, the height of the valve stems is critical on this engine, I think Gary has a spec on that. Many machinists grind off some valve stem after grinding the valve face and seat, and do this to compensate, but most never measure it, they just guess how much, Also, there are differing valve lengths depending on the chamber size, so you can’t mix and match from different heads unless they are same application. The block is the simplest one on the planet, it holds crank and pistons, and the oil pick-up tube, everything else was on the accessory drive housing or on the head!
Let me know what your plans are regarding cam followers, there’s some stuff to beware of.
A: is right on the valves. I had two heads done and both times the supposed machinist ( owner’s brother ) ground the tops down by eye. You could look down the row of valves and see that they all were different lengths. According to a good source the following are the lengths:
66 1bbl 4.9 67 1 bbl 4.9 67 4 bbl 4.99 68 1 bbl 4.8 68 4 bbl 4.9 69 1 bbl 4.8 69 4 bbl 4.9
I am sure someone will correct me if these are wrong. If you have someone do your head, make sure they know that the clearance is critical. I guess the SOB that ruined both of my heads thought he was working on a tractor. The valves were so far off that the cam cover would push up during preliminary testing.
A: the weird pipe is the Y-pipe from the dual outlet manifold that the factory used on all Sprints.
Any proposed updates, changes, pictures, and/or corrections, please use our comment section below (may need to click on permalink to access comments feature). Information is subject to change and offered as is without any warranties or guarantees. Please review our Term's Of Use for more information.
Content last modified: January 16, 2014 at 2:57 pm
Q: OHC Conversion to V-8
OK gang I really need some help here. I’ve been looking for a 1968 convertible 400 car for about a year now, however I’ve not been satisfied with the condition/options of the cars for the $. Consequently I’ve entertained the idea of just building my own. I am somewhat of a purist so I don’t want to screw up a nice/clean original example. So I found a reasonably clean six cylinder convertible, non matching #’s OHC six. It does have a four barrel, but its not a SPRINT option, 3 speed manual on the floor. No PS, PB, manual top. I’m planning on building the car and keeping it forever, so I will not try to pass it off on anyone else. Here’s what I want to do/ am consiereing. 400 or 455, streetable that will run mid to low 13’s. Engine cam intake carb ect I’m fine with questions I have are: Will the existing 3speed work with either engine?(I am not a total idiot but just figured I’d ask) if not which manual trans, should I use? Where to find and how much? I haven’t ruled out going to a 4speed auto( like the one in HPP 1967 Goat) opinions on this welcome if anyone has tired it. IT has manual drum brakes(recently rebuilt/lines cylinder ect works great) are they sufficient or will I need to upgrade to account for extra weight of V8 trannie ect. Suspension: new front/rear springs? I know some guys like 6 cylinder springs for weight transfer. Suggestions? Or other issues I have not considered any and all advice is greatly appreciated.
A: You asked earlier about converting to a V-8 and stick. There are differences in the clutch setup between the OHC-6 and a V-8. The z-bar is longer on the OHC-6 since the block is narrower. Also a OHC-6 runs much better with the correct 4-speed, which will not last long with a V-8. They originally came with a Saginaw with a 3.11:1 first gear ratio. Most Muncies used a 2.55:1 first ratio. Going to a steeper rear will work well with both engines. The OHC-6 will rev higher, but it stops making real power around 4500 RPM.
A: I can tell you the transmission behind a six is a Saginaw 3-speed, very light-duty, not likely to hold up behind ANY V8! Also, the OHC6 has a different bell housing and probably different Z-bar than the V8 applications, so to do a 4-speed, you will need a Muncie to be period correct, or a Borg-Warner T-10 (I think the T-10 may be a little stronger), and most of the rest of a 4-speed change-over. The 700R4 Automatic is a good transmission, but only comes in a Chevy bellhousing pattern. The 200-4R is run behind VERY hot V6 Buicks in drag racing, but you’ll have to do some research to see how they do that, it does come with a dual-pattern bell housing. The 200-4R also fits better, Gary installed one in his 1967 Tempest Sprint with no chassis mods, just moved the crossmember back to an existing set of holes in the frame. There are no additional holes in the ‘bird, but it is still likely to be easier to make a 200-4R fit than a 700R4. The driveshaft even stayed the same in the Tempest!
Also, although drum brakes are, shall we say, adequate, there may come a time when you need MORE than adequate! You will NEVER regret changing to disc brakes! Especially after going through a puddle and having NOTHING! You’d have to be a bit of a daredevil to have drum brakes in a car capable of turning low 13’s!
By the way, I would probably be interested in aquiring the bell housing and Z-bar from your OHC6 after you remove them, as well as the flywheel, and any other six-specific related clutch parts.
Any proposed updates, changes, pictures, and/or corrections, please use our comment section below (may need to click on permalink to access comments feature). Information is subject to change and offered as is without any warranties or guarantees. Please review our Term's Of Use for more information.
Content last modified: January 16, 2014 at 2:59 pm
Q: Rebirth of OHC-6
I have a 1968 Firebird with a 250 O/H cam 1bbl carb. And am having some serious running problems, so am considering dropping the 400 pontiac engine I have (from a newer Firebird) into it. Will a 400 bolt up to 250’s stock tranny which I believe to be Pontiac’s 2-speed (automatic, no a/c) or maybe powerglide.(Did Pontiac put Powerglide’s in, in 68?
A: Tom Can I ask why you want to change the motor if the OHC-6 is repairable? You have alot of other things to consider when doing this swap such as,motor mounts,tranny cooler,larger radiator,rewire the engine section of harness, cooling baffles around the radiator. An a/c equipted car is easier to change as it comes with these baffles regardless of the orginal power train. Not enough of the OHC-6s left… This motor basicly revolutionized the industry as it is the basis of most OHC-6s(4 and 6cyl) today.
A: Fixing of Problem
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I would suggest first looking at the carb. The carb setup sometimes causes a vacuum leak towards the cam cover, due to the stud being difficult to reach. The idea of a steel gasket would solve this problem. The second area that I would look at would be the vacuum advance on the distributor. If it gets gummed up, it won’t release correctly. Just some ideas.
I don’t have the carb numbers with me, but I will try and get them for you. There were I believe four different carbs used: automatic, automatic with air, manual, and manual with air. The air condition carbs used a solenoid to adjust the idle while the air was on. If you need a carb, myself and several others on this list have a bunch laying around.
History of Engine
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The OHC-6 engine is often misunderstood. The belt was the part that worried most new car buyers between 1966 and 1969. Unfortunately, the belt holds up very well, it is the oiling system that needs work. Oil starvation of the top end (i.e. camshaft) causes many camshafts to be wiped out. The engine came in two versions, a 1-bbl base engine with a 9.5:1 compression ratio and a 4-bbl “Sprint” version. The Sprint version included a 10.5:1 compression ratio (determined by the cylinder head), dual valve springs, a 4-bbl Quadrajet (the first production use of this carb), a high-lift camshaft, and dual exhaust manifolds. The Sprint version was rated at 215-230 HP depending on the year. The engine was 3.8 litres (230 CID) in 66-67, and 4.1 litres (250 CID) in 68-69. The best engines to build up are the 1968 blocks.
Hot-Rodding
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Most OHC-6’s that are still around are 1-bbl automatics. I believe this is due to the fact that these cars were not beat on as much as the 4-bbl/manual transmission versions. With an advertised redline of 6500 RPM, the manual versions tended to be abused and have the oil problem noted above. The ideal engine to build with today’s gas is a 1968 block with a 9.5:1 cylinder head. A Sprint intake and exhaust complete the package. Finding the correct carb can be a “challenge”. It seems that most of them have disappeared, with the exception of a few expensive NOS pieces. A standard Pontiac (fuel inlet on the front, not side like Chevy) Q-jet can be modified to work with the OHC-6, I will be doing this soon, and will let you know the details.
If you plan on converting to a manual transmission, the four-speed, the z-bar and the transmission are different then the V-8 version. The z-bar is longer to accommodate the difference in engine width, and the transmission uses a 3.10:1 first gear. This is very important in getting good performance from a standing start with a Sprint. The automatic that is used with the OHC-6 is a Super Turbine 300, which is closer in relation to a THM350 then a PowerGlide (from what I have been told). There are two versions of this transmission, an air-cooled used on the OHC-6, and a water-cooled used with the V-8’s. The transmission was also used in various Buicks and Oldsmobiles, and it is getting a little difficult to find anyone knowledgeable about these transmissions, or to get parts.
There are a few companies that offer speed parts for the OHC-6. The most notable is Clifford that produces camshafts, headers, and Weber carb kits. Although the engine will rev to 6500-7000 RPM, the usable power of the stock setup is closer to 3000-4500 RPM, as it runs out of breath any higher (although neat noises will happen !!!).
I hope this information has been helpful. I don’t want to get a reputation for ranting (although this one is a little better organized!), but a healthy OHC-6 is a beautiful thing. The folks on this list will have tons of information about this engine, as well as anything else you will need for your car.
Any proposed updates, changes, pictures, and/or corrections, please use our comment section below (may need to click on permalink to access comments feature). Information is subject to change and offered as is without any warranties or guarantees. Please review our Term's Of Use for more information.
Content last modified: January 16, 2014 at 3:09 pm
Q: More OHC6 Rebuild Questions
OK, I think I have an idea of what to check, but still have some questions:
1.) The valve height should be from the top of the head to the tip? I would think that this is done without the valve springs. Is that the best way to measure?
2.) What is the oil restrictor? Where is it located? How can you tell if it is bad? I lost two camshafts (worn lobes) due to low oil pressure, so I want to make sure that my 230 HP Sprint cam will survive.
3.) Where is the 30 vs. 45 mentioned earlier? Valve angle doesn’t sound right, since they are perpendicular to the head. I have one ’66 head, two ’67’s, and one ’68; are they all the same in terms of performance and oil flow? Numbers don’t matter much, since very few people even know what the numbers are to be.
4.) What type of work do the cam followers require?
5.) What type of prep work should be done to the lifters? I know they can be disassembled and cleaned, and was planning on doing that, but is there an easy way to check the leak-down rate?
6.) Are rings and pistons still available? I know that one of the three engines that I have needs new rings. I was going to use the best parts of the three to make this new engine. What is a safe overbore? Does this cause any overheating problems like the V8’s?
7.) I am converting from an automatic to a four-speed. I have found the correct transmission (3.11:1 first) and all of the clutch parts. Someone asked about the Z-bar being a different length, that is correct, to compensate for the different width of the engine. Will the driveshaft have to be shortened? The manual for 1967 shows that they have the same “stripe”, so I would think they are the same. How about the yoke. Is there anything I have to worry about here? The transmission I have doesn’t have the yoke, so any ideas on where to find one?
A: Okay, I’m now back to the top of your letter after answering all your questions, and one theme runs through all those answers: INFORMATION!! Our experiences are always mixed with good documentation from Service Manuals and other forms of the printed word and number! We would not likely have learned so much without finding way more info than we could just looking at parts, so EQUIP yourselvles with a small personal LIBRARY regarding your car and automotive knowledge in general!
Albert Einstein said something like “Why bother remembering that which you can alway look up?”
1) Yes, from the top machined surface that the cam cover gasket sits on to the tip of the valve, but WITH the valve springs installed at the completion of the valve job. This info MUST go to the machinist who does this work!! If he is not willing to listen to your input regarding this stuff due to pride (“I’m not having some stupid customer tell me how to do MY job!”), FIND ANOTHER MACHINIST!
2) This is where the 1967 Service Manual becomes valuable! It describes, in words and pictures, how this system works. There’s a passage through the head with the restrictor, it’s between cylinders 2 and 3, and it is a piece of tubing about 2 inches long with an hourglass-shaped crimp in the middle of it that is about 1/8″ internal diameter. It then has an .080″ hole drilled in the side of the crimp, and the sizing of both the drilled hole and the hourglass crimp are critical to the flow volume and the pressure of the oil being fed to both the camshaft AND to the lash adjusters (lifters). Sometimes when poking around the holes and passages of a head being cleaned, these are damaged. They are also a bit fragile to try to remove from a head that hasn’t been hot-tanked enough to let it come loose.
3) Numbers MATTER ABSOLUTELY! The cylinder head numbers (to I.D. heads) are listed in Pete McCarthy’s first book, written for drag racers around 1981, including the NHRA minumum cc’s for racing, gives a good idea of which heads are which for mix-n-match engine building! I’m sure they’re in the parts books as well, send me your numbers, I’ll help you choose a head. The 30 degrees and 45 degrees refers to the valve face and the valve seat; when the machinist actually grinds on your head and valves, he’s cutting a surface that is angled. The only heads that are 45 degrees are the second design for 1969. All previous heads used the 30 degree valves. If there’s any doubt, give me your head casting dates as well. PS Ever heard of a 3-angle or 5-angle valve job? That helps shape the valve seat area for a smoother flow from the port through the valve. You cannot see the angle with head assembled, the valve need to be removed!
4) The current replacement followers have a rough and uneven surface that rides against the camshaft, and need to be machined smooth. I did mine on a veryfine knife sharpening stone, one-by-one, by hand. That takes a lot of cutting oil and from 1/2 hour to 45 minutes per follower. Jerry Woodlad describes this in more detail in his literature.
5) I use new lifters, they are a slightly different design, meaning they don’t have that little pin in the top hole, and you can’t mix-n-match with these.
6) Pistons for a 230 I believe are still available, but for 250’s have been difficult to find for some time. Safe overbore depends on the casting quality of your block, this applies to ANY engine! Usually try to stay at .030″, if you can find them, you might be able to do .040″, and I have done .060″. The rings are standard sixes to the industry, even the 6-cylinder Chevy used the same ring size, and even the same rod and main bearings! In my 250 inch engines I have also used modified pistons from a 307 Chevy V8, and there’s a piston in the 4.0Liter modern Jeep engine that may be usable. Its standard size is .005″ larger than our stock piston, 3.88″ instead of 3.875″. I haven’t got one in my hands for comparison yet.
7) Your driveshaft and crossmember should be the same. The only different crossmember was for the THM400, all others used one member, that covers all 3 years, 67-69.
Any proposed updates, changes, pictures, and/or corrections, please use our comment section below (may need to click on permalink to access comments feature). Information is subject to change and offered as is without any warranties or guarantees. Please review our Term's Of Use for more information.
Content last modified: January 16, 2014 at 3:10 pm
Reference:
- 1967 Dealer Technical Bulletin 67-T-13
- 1968 Pontiac Service Manual figure 6-18
- 1968 Dealer Service Information Bulletin 68-I-68A
Content last modified: September 15, 2023 at 11:15 am