'67 327 timing issues

[Dennis O.]

I want to thank everyone on the board for helping me. I have a '67 coupe with a 327/350 that I just had rebuilt. A "professional" rebuilt the engine to the tune of $5500. Since I was building the car to drive, he put in 9/1 pistons and a Comp Cams 262H camshaft. He ran it on his dyno, and it made 336 HP, which I was very satisfied with. However, after the engine was back in the car, it wouldn't run for ****. Turns out that I couldn't get it timed right. Nothing I tried worked; I couldn't even get the thing to run with the timing set to spec. First problem; even though it was a "pro build", he hadn't rebuilt (or even checked) the harmonic balance. It was the old original, and the timing marks had slipped. I figured, "OK, I can get it close with a vacuum gauge" so tried to set it up that way. I couldn't get more than 12 inches of vacuum or get it to run decent for anything. I went through the TDB, and came across the posts about the "dimple" on the distributor drive gear. I pulled my distributor, and sure enough, it was 180 degrees off. I punched out the pin, turned the gear 180, and now everything is fine. I'm sure he ran the engine on the dyno without the shield/coil mounting bracket, and was able to twist the distributor enough to get the readings he got. (I should have known, because when I got the engine back, the plug wires were off one hole on the distributor.) Oh, by the way, this was after I had spent $475 on the local garage that has a very good reputation and all of the "proper" skills and equipment.

This was a problem that seems to be very specific to C2's, but nobody outside of here seems to know about it.

I do have one question; This whole thing has been a real time consuming mess for me. I'm up here in Minnesota, and would really like to enjoy this car the rest of the summer. Am I taking a chance on running the rest of the summer with the current harmonic balancer? I'd hate to have it come apart and tear up my car, but I'd really like to enjoy the rest of the summer and send the balancer out to be rebuilt this fall. Outside of the slipped timing marks, it seems fine.

Again, thanks for information that seems to be available nowhere else.

[Timothy B.]

Re: '67 327 timing issues

Dennis,

Did you verify the TDC mark as slipped by installing a piston stop and CAREFULLY turning the motor by hand to find exact TDC. How did you time the engine when you installed it in the car..

On C2 corvettes there is not much room to work with the vacuum advance between the coil bracket and intake manifold. I am helping someone with a 65 350hp engine with correct ground reproduction cam and we had to turn the bottom distributor gear opposite correct orientation to set the timing..

There is some info in archives about aftermarket cams and how the gear in the rear is not indexed like OEM cams.

I think lowering compression with HP camshaft is a big mistake because the late closing intake valve bleeds off cylinder pressure until higher RPM. The engine becomes very soft and week at low speed with low torque and does not run as good as the original camshaft and 11-1 compression. It will not idle as well either because of the lower cylinder pressure.

[Duke W.]

Re: '67 327 timing issues

Well, at least it will run on regular unleaded.

Duke

[Dennis O.]

Re: '67 327 timing issues

As I said, I built this car to drive, and want to be able to run on the premium unleaded, non-oxygenated gas we have commonly available up here. As I understand it, the 262H is a relatively mild camshaft. I am satisfied with the 336 HP on the dyno run, and since, I've switched the distributor gear, I am quite satisfied with how the car runs and drives. I'll be pulling the balancer in a couple of months to be sent out and rebuilt.

[Timothy B.]

Re: '67 327 timing issues

Dennis,

The 336 hp number sounds good, I am not trying to question your good intentions with the engine or the machinest as he probably builds enough of them to know where to stay safe.

All I am saying between members here is that the engine will run fine with the stock camshaft and 262H camshaft with the factory spec dome pistons. The 262 is probably seat to seat duration figure..

I apoligze if I sounded harsh. Good idea with the balancer repair.

[Dennis O.]

Re: '67 327 timing issues

No apologies needed. Just to get to the bottom of this, are you saying that with a 151 camshaft and stock 11/1 pistons, I could run with non-oxygenated (no alcohol) premium unleaded straight from the pump without retarding the timing? I've had this car a long time and before I had the engine rebuilt, it need race gas every other fill up to run without pinging. It was a pain in the ass to get and twice as much as premium unleaded. That's what I wanted to avoid.

[Donald O.]

Re: '67 327 timing issues

No apologies needed. Just to get to the bottom of this, are you saying that with a 151 camshaft and stock 11/1 pistons, I could run with non-oxygenated (no alcohol) premium unleaded straight from the pump without retarding the timing? I've had this car a long time and before I had the engine rebuilt, it need race gas every other fill up to run without pinging. It was a pain in the ass to get and twice as much as premium unleaded. That's what I wanted to avoid.

Dennis,
I have a stock 1967 327-350 with the original pistons, rings, cam, lifters, bearings, crank, con rods, push rods, rockers. I use the normal 93 premium hell or BP (and around here near Chicago, ALL stations sell ONLY the 10% alcohol), I also use the factory timing. I have no pinging or drivability issues and I do not use racing fuel or aviation gas.

The only mechanical issues have been a broken exhaust valve in 1986 and replaced the clutch in 1997 and faulty vacuum advance units in 1987 and again in 2005.

DonO

[Dennis O.]

Re: '67 327 timing issues

How long have you owned your car? I have had mine since 1987 (It had 61,000 miles and looked it when I got it). How many miles does your car have? Everyone I've talked to about this (and I did quite a bit of research) says that today's pump gas and 11/1 doesn't work very well at all. (BTW, our unleaded premium with no alcohol is 91 octane.)

[Donald O.]

Re: '67 327 timing issues

How long have you owned your car? I have had mine since 1987 (It had 61,000 miles and looked it when I got it). How many miles does your car have? Everyone I've talked to about this (and I did quite a bit of research) says that today's pump gas and 11/1 doesn't work very well at all. (BTW, our unleaded premium with no alcohol is 91 octane.)

I bought it through a Chicago Tribune ad on June 20, 1985. The Vette had just less than 52k miles. It has about 82k miles now.

Just remembered another mechanical issue, had to replace the original plastic coated timing gears around 1989....or so, and the front seals.

IMHO the majority of persons who claim to have all these timing/compression/pinging issues are not the persons I'd let tune mine. Then again, maybe I'm just dumb and lucky

[Joe C.]

Re: '67 327 timing issues

Don't fret Dennis, the camshaft that was installed is milder than the original "151" cam, and was designed to operate with somewhat lower static compression ratio than your original cam. Without complicated dynamic compression ratio analyses, it is safe to say that your "supposed" SCR will do nicely.

I can tell you, with certainty, that if your engine builder had built your mill with (actual, measured/calculated) SCR of 10.5:1, using that X-Treme Energy cam, that the engine would not tolerate it without detonation using pump premium.

Although the 262H is a "nice" cam, closer in character to the 929 than to the 151, the camshaft I would have used in your build, in order to emulate and improve upon the original 151, would have been the Comp "N + L79H", in which case, I would have built in an actual (measured/calculated) 10.5:1 SCR.

Compare the specs on these cams, paying particular attention to the event timing of the inlet valve closing:

http://www.compcams.com/Cam_Specs/Ca...x?csid=85&sb=2

http://www.compcams.com/Cam_Specs/Ca...?csid=110&sb=2

[Dennis O.]

Re: '67 327 timing issues

Finally, a reasonable answer. I think you're telling me that a 151 cam and 11/1 pistons wouldn't be drivable on 91 octane unleaded premium. I don't want to win any drag races, I just want a car that's peppy around town that doesn't need hard to get fuel or any fancy additives. I will tell you this; after the engine was put in the car (after the dyno runs), if I idled it for longer than 2 or 3 minutes, the temperature would start climbing past 200. I talked to the engine builder, and he said that it was just tight, and to give it a few miles. After a while, that problem went away. It will sit and idle for as long as I want and not get past the 210 mark or boil over. I believe the engine is finally starting to get broken in, and would probably pull 350 on the dyno now that it's "loose". I am now extremely happy with the combination I have, and believe I have made the right choice in cam and compression. All I wanted to do was thank the folks on here for making me aware of what I believe is a very rare situation with C2's that I was able to correct and solve my problems. Looking back, I find it hard to believe that I was taken to task for not building my engine to standards that would have resulted in an engine that would not have functioned for the purposes that I needed. Again, Thanks for the cam gear orientation information. It was very useful, and probably not obtainable anywhere else.

[Timothy B.]

Re: '67 327 timing issues

Dennis,

In reading your post about the 262H comp camshaft I assumed the cam specs were similar to the stock L-79. Looking at the actual figures Joe posted on the camshaft the valve timing is like the 929 camshaft.

Again, I apologize if my comments led you to believe I was being harsh. I helped build a L-79 with stock domed pistons and 151 camshaft. Distributor curved to 12 inital and 26* centrifugal all in at approx 3000RPM, vacuum advance 15*@ 12". There is no ping, engine runs strong..

[Dennis O.]

Re: '67 327 timing issues

Again, I will ask; what are you using for fuel? Easily available premium unleaded or something a little more exotic (race gas), or additives? I have an early hemi in my dirt track modified with 12.5/1 compression and an Engle roller cam that doesn't ping either, but it requires leaded premium at near $7 per gallon. I don't want to drive half way across town every time I need to buy fuel.

[Duke W.]

Re: '67 327 timing issues

Dennis,

Looking at the actual figures Joe posted on the camshaft the valve timing is like the 929 camshaft.

Not even close! Most Comp Cams cams are ground with a 110 degree lobe separation angle, so with .050" duration close to the L-79 cam, it has much more effective overlap than the L-79 cam and will certainly not idle like a 929 cam.

I've been applying the principles I use to design the Special 300-Horsepower and McCagh Special camshafts (which you'll read about in the fall issue of The Corvette Restorer) to the L-79 camshaft, and so far I haven't been able to improve it significantly, but I'm not done trying.

Bottom line is the L-79 cam is tough to beat in a L-79.

Duke

[Timothy B.]

Re: '67 327 timing issues

Dennis, He is using pump premium here in MD. Octane is 93 I believe..

I agree Duke, the L79 set up is hard to beat, I am trying to talk brother into wide ratio transmission with his 370 gear..