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.
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Content last modified: January 16, 2014 at 2:57 pm