| Author | Message | ||
| Phil Hughes (Ferrarifixer)
New member Username: Ferrarifixer Post Number: 23 Registered: 7-2003 |
Cam timing is moved by 12 deg for every sprocket tooth misalignmnet. Depending on which cam and which direction the misalignmnet, the effects differ enormously. For peak power and torque figures, timing is not super critical. The rpm at which it is all achieved is the greater variable when experimenting with timing and overlap, and the feelable difference from the seat of your pants. In controlled category racing, and when engines are all identical, gains can be made from tweaking timing and overlap to better fit the power delivery to a given gear ratio. | ||
| Philip Airey (Pma1010)
Member Username: Pma1010 Post Number: 333 Registered: 7-2002 |
Are the factory specs for compression posted somewhere. As part of the cam work, the technician ran a compression test and I'd like to compare nums with factory specs. Thanks Philip | ||
| Dave Helms (Davehelms)
Junior Member Username: Davehelms Post Number: 94 Registered: 5-2003 |
If I would venture a guess, I would bet better than 1/4 of the 308-328 cars are running with the same conditions you have. Maybe not as far off, but close. As long as the emissions are in the ball park, and it is running well, you are fine for now. If you are close to the service interval (5 yrs on the cam belt) use this for an excuse to get it done a little early. If your not close, leave it be, and if the belts were done properly it will be OK until the next time they are needed. So often an owner thinks that their car is running very well until they get a chance to drive another that was serviced correctly, with the cams timed. Setting the timing is a fairly labor intensive operation compared to just slipping the belts on. With all the hipe about what a rip off the cost of a correctly done service costs the customer, you are seeing this "slip the belts on" type service done far more often. The marks on the cams only mean the valves wont hit, and the timing is in the ball park and ready for timing, thats all. When at the factory for 360 training, we watched cam timing being done. I can tell you there is one 360 out there where the cam marks are off by about 1/16" from the correct timing, after we had them recheck and reset the timing on one bank. They had already stamped the cams for the incorrect timing. A simple matter of "consumer acceptable VS exotic". | ||
| Mike Dawson (Miked)
Junior Member Username: Miked Post Number: 116 Registered: 2-2001 |
Another possibility that I haven't seen mentioned yet is that one head (the higher compression one) has been milled sometime in it's life. I have seen the same compression difference before on an American V8 from just such a "repair" after a head gasket failure. | ||
| Andrew A. Illes (Andyilles)
Junior Member Username: Andyilles Post Number: 181 Registered: 10-2002 |
Mike... yeah, a timing belt change is a wonderful opportunity to bump timing, if done carelessly.. wouldn't take much to get your readings. On the bright side, it's hardly fatal as any misadjustment seems minor, from your descriptions. How far are you from Tucson? Bob Wallace there is a fantastic "natural" wrench... started with the Lambo factory before my wisdom teeth came in, and he builds "exotic" engines now. Sure he'd help, though be prepared.... he's old, cranky and anal these days... a bit of a curmodgeon actually... and you can tell him I said so, lol. But you'll NOT find better work anywhere!! | ||
| Mike Procopio (Pupz308)
Member Username: Pupz308 Post Number: 470 Registered: 10-2002 |
Uggh... I'm in way over my head--there's no way I can do this. Lots of info on this in the archives... Here's one procedure... http://www.tedgage.net/ Ferrari of Central Florida last changed the timing belts June 2001. Would they have set the timing wrong during a timing belts / tensioner bearings change? | ||
| Mike Procopio (Pupz308)
Member Username: Pupz308 Post Number: 469 Registered: 10-2002 |
Thanks for the clarification, Andy--and to all for the help. I'll look in to this--I don't know how to set the cam timings, but I've got some contacts who do. In the mean time, are overlapped cam timings something to cause damage and/or excess wear on the engine? | ||
| Andrew A. Illes (Andyilles)
Junior Member Username: Andyilles Post Number: 179 Registered: 10-2002 |
Mike... What David is basically saying, and others suggest, is that the cam overlap is different on your banks, and I'd agree. To have those readings, something has to be a common denominator for a whole bank, and that can only be the cam timings. Do you know how to degree them? If so, I'd suggest doing that... if not, find someone who does. Best regards, Andy | ||
| Dave Helms (Davehelms)
Junior Member Username: Davehelms Post Number: 91 Registered: 5-2003 |
With the emissions in the ball park, it is not a full tooth off. When that happens, the car lopes at idle like it has a race cam. Has is right with the cam timing though. It is most likely off by a few holes on the cam gear. The 150 readings at 5K altitude is not too bad. That would lead me to believe the high compression bank either has advanced intake, or retarded exh. timing (better chance the intake is off) Usually the sample tubes (exhaust)on the early cars are either plugged or broken, so I drill a 3/16 hole in the exhaust pipe after the collector, and take a sample of the exhaust at that point. That way you are looking at a whole bank and not just one cylinder. The exhaust sample will show one side or another that has high levels of HC (unburnt fuel). This will be the side with the wrong cam timing (IF the carbs are all set up properly already). Weld a couple of nuts over the holes drilled, and put bolts in them to seal up (you will need them again some day, usually for emissions setting) Taking a compression test on the 308-328 cars before a major is std practice. The compression test will show which cars need the cams degree'd, rather than set by the marks every time. | ||
| Hans E. Hansen (4re_gt4)
Intermediate Member Username: 4re_gt4 Post Number: 1595 Registered: 4-2002 |
My carb 308 showed 165-170 on every hole. | ||
| Mike Procopio (Pupz308)
Member Username: Pupz308 Post Number: 459 Registered: 10-2002 |
Stacy, Interesting. What altitude (elevation) are you at? Very curious that we're getting a 25psi difference in the front bank vs. rear bank... Like yours, my car is running really well. I think I might have to invoke some "I bought from a dealer" priveledge and call Ferrari of Central Florida and speak to one of their from-the-factory Italian mechanics about it... See what they say. If there's a property coming up on two carb 308s, it could probably be seen on others, too!  | ||
| stacy o'blenes (Stacy)
Junior Member Username: Stacy Post Number: 71 Registered: 8-2001 |
Mike, I don't know if this helps or not but I did a compression test on my 77 308 this spring. On my guage I got compression readings of exactly 150 on all cylinders on the front bank and exactly 125 on all cylinders on the rear bank. The car is running well. I am going to do a valve adjustment this fall and will check the timing marks on the camshafts at that time but like you I am a little puzzled. | ||
| Mike Procopio (Pupz308)
Member Username: Pupz308 Post Number: 458 Registered: 10-2002 |
Have not checked cam gears... Is this different from getting the "timing marks aligned" (which I think you do when changing belts)? Somewhere, there's three or five little marks (depending on year) that have to be just right... | ||
| Joe Craven (Rscapri2600)
New member Username: Rscapri2600 Post Number: 17 Registered: 7-2002 |
One or both of the cams might be a tooth off. Have you confirmed if the cam gears are installed properly? | ||
| Hans E. Hansen (4re_gt4)
Intermediate Member Username: 4re_gt4 Post Number: 1591 Registered: 4-2002 |
Supposedly......... I'll defer to others as to how this might get out of whack. | ||
| Mike Procopio (Pupz308)
Member Username: Pupz308 Post Number: 457 Registered: 10-2002 |
Cam timing... This is something that's not normally "adjustable", right? That is--there's one correct position based on the timing marks? | ||
| Hans E. Hansen (4re_gt4)
Intermediate Member Username: 4re_gt4 Post Number: 1588 Registered: 4-2002 |
Just a guess: With numbers similar on each *entire* bank, it must be cam timing. I can't think of what else would affect all cylinders equally on one bank. | ||
| Mike Procopio (Pupz308)
Member Username: Pupz308 Post Number: 456 Registered: 10-2002 |
Right. Front is 5 through 8. I should add that I'm at 5000ft, where atmospheric pressure is approximately 83% the value of that at sea level. So normalizing this rougly to sea-level standards, I'm getting 150/.83 = 184psi in the lower cylinders. Again, this is will the accelerator down all the way to the floor for each cylinder--I'm assuming that the throttle plate was all the way open under these circumstances. Of course, absolute compression PSI measurements are not meaningful in this case, as a variance of even +/- 20% among different gauges, human readers, is possible. The relative measurements (with the same gauge) across the cylinders are meaningful, though... Has anybody seen results like these--or could explain the consistent but different readings across the two banks? | ||
| Phil Hughes (Ferrarifixer)
New member Username: Ferrarifixer Post Number: 7 Registered: 7-2003 |
Just to clarify, the rear bank (right hand) is at the rear of the car, seems obvious, but is No.s 1-4. 5-8 is the front bank (left hand). The throttle should be held wide open when doing this test. Your 150 readings are too low, it could be the cam timing/overlap being incorrect. The far better test, as always is a cylinder leakage test, not compression. Do this and you're looking for no more than 15% leakage, with as little as 3% being perfect, and 10% is still healthy. | ||
| Mike Procopio (Pupz308)
Member Username: Pupz308 Post Number: 455 Registered: 10-2002 |
I recently did a compression test with my mechanic. Here's what we did. 1. Remove all spark plugs. 2. Disconnect coils. 3. Attach guage to each cylinder, one at a time. 4. Clutch in, accelerator pedal floored-- 5. Start car, about 5 seconds, take reading We got some very interesting results: FRONT BANK: 1:170 2:170 3:175 4:175 REAR BANK: 5:150 6:150 7:155 8:150 We tested twice--going back and forth across banks; we always got these same results. I know enough to know that consistent readings are good, say, +/- 10%. What I don't know is, what the difference between the two banks means, and what could case it... Should I be worried about this? The car is running very well now, decent emissions, though we did recently replace one plug on each bank for fouling--one was oil, the other was wet w/gas. Now on 8 cylinders after having opened up each distro cap, snipped the ignition wires, replaced and used some dielectric grease. 1978 308 GTS, Carbed, ANSA exhaust Thanks all... --Mike |