Change timing belt w/o open cam cover???

I don't recall seeing any markings on my 328. It sounds like the mechanic let a camshaft rotate a tooth on him.

Many years ago I was changing the timing chain on a V-8 Merecedes of mine. I let one of the cams slip one chain link. As it was getting late and I was very tired and needed the car for work the next day, I took a wrench and rotated the crank to convince myself there was no interference. I drove the car for a few days until I had the time to correct the out of time cam. The difference in engine power/torque was quite noticeable with one camshaft off one chain link.

 

I would almost be willing to bet that the 5/8 exhaust cam is no longer in time. As soon as you remove the 5/8 belt that cam will rotate about 1-2 teeth on it's own.

 

GET a NEW MECHANIC! That guy has no idea what he is doing. These is another one of those things that screw up ferraris and give a bad rap. You need to properly time the mechanicals by at least using the proper Ferrari timing marks. Bringing the #1 piston to TDC and then pin the camshafts on their marks on the cam journals. The lock pins must be removed from the cam cogs and then the belt placed and tensioned before the cam gogs are reindexed and secured. That is the right way to do it.

For the super anal use a dial guage etc...but that is more complex.

 

There are alignment marks on the back of th cam gear mounting flanges. They are made to be aligned with marks on a a factory tool that sits on the cams of the 2V cars. w/o the tool, the marks are very hard to use. There are much easier to use marks on each cam that align with matching marks on the cam journal cap closest to the cam gear end of the cam. You can see the rear bank intake cam's mark & corresponding journal mark thru the oil filler hole in the cam cover when the engine is on TDC. (Flywheel is on the PM 1-4 mark).

It is possible to change belts while preserving the original timing. This should only be done IF YOU KNOW THE CAM TIMING WAS SPOT ON TO BEGIN WITH, and are extremely careful to keep the cam gears from rotating.

I & several other Fchat members have done it. You should NOT have to change the cam gear pins if everything is kept locked down & the original positioning is preserved. It's done routinely on a lot of other twin-cam cars, but most of them have provisions for locking the cam gears in place while doing it.

Sure sounds like your mechanic is off by a tooth on at least one cam. Or possibly managed to be off a tooth on the drive gear, making both cams off by a tooth! Most likely the front (5-8) bank inlet cam as it does want to rotate on the least pretext. Also, remember that 2 of the cams drive the distributor points, so changing cam timing also changes ignition timing.

A noticeable power drop is grounds to take it back to him & demand he correct it.

 

Verell wrote:"I & several other Fchat members have done it. You should NOT have to change the cam gear pins if everything is kept locked down & the original positioning is preserved. It's done routinely on a lot of other twin-cam cars, but most of them have provisions for locking the cam gears in place while doing it."

Verell,

We had a similar discussion under the FC super ferrari section on F40 engine rebuild don't do this at home. My statement then as well as now is yes you can do this with the cogs in the pre-belt removal position but just because you can do it does not mean it is right. Additionally, it is more difficult to make sure the other guy was spot on than to just make sure it is spot on yourself. Reinexing pins on cogs make up for wear, belt stretch, blah blah blah...and properly tensions the belts. It does make a differnece in a car that runs o.k.. as Dave Helms puts it "consumer acceptable" vs, the way it should be to run at peak performance. The key to reindexing cam cogs is the it PROPERLY tensions belts. By doing it the way you suggest you cannot properly take up the slack between cams and tensioners. Try it my way you will see that there are very few camshft degrees between the pin hole that fits and the one that can be forced to fit. In fact it is really easy to do it with precision. Look at this mechanics mistake. He either did not have the time to do it right the first time or he did not know how to do it right the first time. Under those conditions when is he going to have time to do it right the second time and I bet he does not understand this thread we are discussion or he would have done it right the first time.

 

Patpong,
The same happened to me. Just take it back to the mechanic and tell him to check the timing, and tell him you lost performance. Rifledriver is probably right on with his assumption.

Jim

 

Nothing is more irratating than when you know your car well, someone f's up the way it runs and then tells you its fine. A good mechanic returns a car that runs far better not one that runs worse, attention to detail is everything.

 

That statement sure hits home with me! When I used to have a mechanic, I would always pray he didn't screw up the car fixing whatever he was doing, but it almost ALWAYS had a new problem caused as a result of his solving the old problem. I am now my own mechanic, and maybe I have to do things 2 or 3 times as I'm learning like the pro, but my time is cheaper than his!

Ken "I can screw up my car for a lot less money than my mechanic, and fix it better too" Butler

 

It is absolutely correct to re-index the cams of course. (And if you're going to index them, then you should really use a dial gauge in case the marks are not right!!). But on a carburettor car you can check the ignition timing BEFORE doing a "belts only" change. Make a note of it, then replace the belts (if that is the owners request), and then re-check the ignition timing.

This will show you exactly in CRANK degrees (which is at least twice as accurate as cam degrees, and probably more due to large radius of flywheel) if the timing has altered due to the new belts being "different".

In my experience, if the old belts were just old and not worn, the ignition timing will not change AT ALL. So as long as you know the car was right before, IT WILL be afterwards. If the igntion timing moves at all, it will most likely advance itself 1 -3 crank degrees as the new belt may be less stretched than the old. If this happens you know the cam timing has moved too, but only by 0.5 - 1.5 degrees. Now ask yourself, "When the cams were dialled in previously, were they done on an old belt or a new belt...."

Advancing all 4 cams by 1.5 degrees, (3 crank degrees) typically move power and torque peak figures approx 25-50 rpm lower.

Owners are not obliged to remove the covers for every belt change. Some cars cover only a few km between belt changes, or a car may be sold and the new owner insists on fresh belts being fitted. There are many legitmate reasons to do belts only, more so than to remove covers every time.

It is absolutely not necessary to remove the covers every change, AS LONG AS YOU KNOW THE CAR IS RIGHT TO BEGIN WITH AND THE TECH PUTS ACCURATE MARKS ON.

To replace the belts on a 308 takes approx 6-8 hours with A/C. It can be done quicker too if everything is like new in there. But to remove the covers and dial the cams in will take up to 40 hours to complete.

Now, I make a living on an hourly rate, but it is in the customers interest to give accurate advice based on known facts and experience.

This new 430 thing is really going to bugger some mechanics...hydraulic valve clearances, chains...oh dear, how are we going to make any money now!!

 

hopefully after he "opens up" your valve cover(s)
you won't be left with additional problems

like leaks