308 timing belts installation question...please help - Ferrari Life
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post #1 of 8 Old 01-07-2004, 07:42 PM Thread Starter
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308 timing belts installation question...please help

hey everyone...
i replaced the timing belts on my 85 308 GTS but i did not put everything in top dead center. i locked the cam pullies and crank shaft pulley in place before removing the old timing belts. so my question is, did i do anything wrong? im worried that i should have adjusted the cam pullies to be at TDC instead of just marking each pullies like i did...all help is greatly appreciated...thanks.

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post #2 of 8 Old 01-07-2004, 10:22 PM
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I would have thought this would be OK, but just a lot more risky.

Try turning the crank by hand (DON'T start!) until you get it to exactly TDC, and then check each of the cam pulleys. If everything went in as supposed to then the 2 cam pulleys should also have both rotated to TDC. Given the size of the belt teeth it should be pertty obvious if they are 1 or even 2 teeth out.

Hope this helps.
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post #3 of 8 Old 01-08-2004, 10:44 AM
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Yeah, you should have set everything to TDC before the job, but what's done is done. Let's move on. I think 4kids3fish has the right idea. Put it at TDC and check the marks. Turn it over BY HAND 2 crankshaft revolutions, the marks should still line up.
Let us know how you make out!

Capt. Pete
'79 308 GTS, '82 Jeep CJ7 Jamboree
"Time is what prevents everything from happening all at once."
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post #4 of 8 Old 01-10-2004, 10:22 PM
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If everything was locked in place, you should have no problems, although, it probably will be a good idea to check the marks if they line-up.

When doing the belts on my car and using the marks (not locking down), one cam had a tendancy to shift off the mark after doing the required "two-revolutions-by-hand-before-tensioning" procedure outlined in the manual. Thus, I had to re-align the cam pulley by unbolting and selecting a different dowel hole to bring it back up to the mark.

For utmost precision and performance, use a degree wheel than relying on the cam marks. Its known that they can be off (but we're talking minute inaccuracy - minutes rather than degrees). When doing so, set the valve clearance to the timing specification, not operating spec (eg: 308 2-valve: 0.02" instead of the normal 0.008-0.012"), return to operating spec when complete. The reason for this is to remove the gradual ramp-effect of the cam under operating clearance. Timing clearance causes the dial-indicator to show a defined point of valve opening.
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post #5 of 8 Old 01-12-2004, 01:10 PM Thread Starter
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thanks for the help guys....when i get a chance, i'll do what you all have mentioned and let you know how it comes out....thanks again
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post #6 of 8 Old 01-12-2004, 03:55 PM
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All I can say is I admire you guys for having the courage to DIY a Ferrari. :-?
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post #7 of 8 Old 01-12-2004, 04:29 PM
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Like Peter said...a degree wheel is the most acurate. When I did my TR the plan was to use the engine builder's marks on the cams/caps as my guide. During this time I consulted other enthusiasts on "other" messege boards and was given tons of conflicting "advice" on what the proper or best technique was. Many said not to trust the builder's marks and use a degree wheel. So I did, but it wasn't totally necessary because when I had everything set, the builder's marks lined up perfectly. Peter is also quite correct in that the marks can be slightly off, but not enough to worry about. Just for fun I measured the degrees from one edge of the mark to the other....but still keeping them overlapping, and it amounted to just over 1 degree of crankshaft rotation. These overhead cam engines are quite forgiving and you can be off by 3 degrees and still run fine. Another difficult issue is setting up the dial indicator parallel to the shim bucket travel. I had to make a special offset indicator point, and a plate to mount the indicator to the head at the proper position. But once done it's kinda fun dialing everything in. You have to check valve operation at 0.5mm clearance. Rather than swapping shims into the bucket to get this clearance, simply install another shim to take up all slack, then "zero" the indicator on the shim bucket when the cam lobe is 180 degrees away or pointing outwards from the bucket, and then read the degrees once the indicator moves by the magic 0.5mm or .020" of an inch. Lastly if you do time the cams with a wheel, be sure you use the correct spec.s for your car, don't use Euro spec.s for a U.S. car, etc. Sorry to ramble on here......just wanted to share my experiences.
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post #8 of 8 Old 02-27-2004, 08:37 AM
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:P Actually, just to stir things up a little, I have heard that to get a little more horse power out of a US car, namely the detuned 78',79' and early 80' 308's a person can re-index the cams to European specs.

The results are positive for the intake side but unfortunately the results aren't as much as expected on the exhaust side because the lobe configuration on the US cam is more conservative in duration and valve timing is different due to US emissions criteria.

I am contemplating trying that when I do my timing belts in the future. In order to get a good idea what the effect will be I will be putting the car on a dyno next week to establish a baseline. Should be fun to see what a carb rebuild and cam tweeking will do.


308 V-12 Conversion click here.
"Oh yes, that is one of the very best ways to break these and it is also pretty dangerous. You really shouldn't do that". - mk e.
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