Wanted to make sure I correctly identified the timing marks for ‘79 308 GTB. Attached image of flywheel at PM-1-4 and cams in next post Also included valve clearances - seems all exhaust are just under min spec of .012” A few intakes are fair under spec min of 0.008”. Wondering if worth to change out all the shims to get them within spec? Thanks Steve Image Unavailable, Please Login
Cam timing is so far off it looks like Ray Charles set it. Comical. If you are not going to make clearances correct why did you open it and measure them?
This is first Ferrari I have worked on and wanted to get opinion on measured clearances and timing marks. The 0.012” min for exhaust is rounded up. My feeler gauge at 0.011” slides in fine but 0.012” does not. I assume the clearance is close to the 0.3 mm (0.0118) min. However, other threads have stated the exhaust should be loose and set at the high end of 0.014”.
In other threads they are wrong. I am factory trained and been doing this for over 40 years. Factory says 10-12 set it 10-12. They have very good reasons for saying that. Not really going to go into cam design here. Your big problem is that cam timing. Its a mess.
Duners, this is the page from my 308 carb WSM metric 0.20-0.25mm = 0.008-0.011" 030-035 = 0.012-0.014" use the feeler gauge as "go" "no go" and what goes is the reading. You do not need to worry about timing because those marks are not that far off such that all you need to make the measure is to be on the cam lobe base circle and that's a lot of degrees. You measure then pull cam shafts measure the shim, do some math and buy or swap shims to get in the range needed. Some use a dorky hold open thing to get to the shim but to me way more work than taking out shafts and I think you get better assembly and timing when cogs are loose and can be pinned in exact positions as needed when new belts go on. It's not the only way just my way. Your marks are off from the factory "assembly positions". We do not know why? It is possible that this is the cam timing or other reasons because we do not know who messed with motor in past. 308's work just fine when the assembly marks are used as "timing.". The more precise the mixture control, as in late model ferraris or the blast furnace that is the ferrari 355, the more important is mixture control and therefore real "cam timing" with a degree wheel and dial gauge. You can do that if you want for more precision. Yes there are those who think closer to 0.014 " is a better number but there is no discernible power advantage. Hope that helps... Image Unavailable, Please Login Image Unavailable, Please Login
My dad had changed out the timing belts previously and never pulled the cam covers. I assume he didn’t lock down the cams when changing belts and the off timing was due to him. He did the job on his own and recently passed. He did put it back together and couldn’t get it to run right. He assumed it was due to the carbs. It does seem the off timing was more likely the issue. Thank you for the advice and I plan to pull the cams, adjust valve clearance, and reinstall as close to assembly timing marks.
People are scared to remove the cam cog bolts and play with the pins. There are other pages on Fchat where I have gotten pretty heated with a guy who understand math but not how real world application can force you to pivot to get a job done well. Belts do not move nor do they stretch appreciably and they can't otherwise timing would be all over the place. So in theory if the belt comes off perfectly timed the next belt goes back same place perfectly timed. The rub is the real world of forcing a stiff new belt and get equal pressure over each belt span. Theory departs from reality. Your dad probably put the belt on right up to the point that the new belt stiffness caused him to guess because a cog tooth was 1/2 way between 2 teeth on the belt. Then that error magnifies its way over the other cogs and voila everything is off. That's why I advocate putting crank at TDC, pin cam shafts to their marks. Then place belts with free wheeling cogs, then tension the belt letting the pressure between all spans equalize then pining the cog to the camshaft in the best new location. That may sound like greek but if you study the car you will see it. I'm in palos verdes. If you get stuck contact me.
The introduction paragraph in your Profile suggests that you might have some serious sorting to do (thanks for including it). If this is a US version and the air injection system has been removed/disabled, it would be a little less risky to have the exhaust valve clearances slightly under the minimum, but, if you are sorting some anyway, would be best to get them all in spec. If the cam sprocket is off 1 tooth relative to the belt, that moves the timing mark on the cam a little under 5mm (relative to the fixed mark on the cam cap) -- based on that, I'd say that 3 of your 4 cams are off 1 belt tooth, but the 4th cam being off just a little would indicate that someone thought the factory cam timing marks weren't right, and someone messed with it before your Father's purchase (or a replacement belt had a slightly different pitch). As a starting point, you could just pick the cam sprocket to belt relationship on each cam (at PM1-4) that makes the minimum displacement at the cam timing mark, but you may eventually need to actually measure (and/or reset) the cam timing (if it doesn't run well). Good luck with getting it sorted!
The floating cam pulley makes sense and sounds like the best way to get timing dead on. Thanks for letting me know your local - always nice to have expert on speed dial.
I'm just a DIY guy but been working on Ferraris for 40 years and SCCA clubracing 20 years, so can fix most things.
I pulled the three cams and getting stuck with the front bank exhaust. The dipstick tube is in the way of removing. Do I need to remove the dipstick tube or head studs? Image Unavailable, Please Login
I'd remove the dipstick just for better access -- and to have an easier job putting the 5-8 camcover back on.
From reading other threads about dipstick removal it seems to be a pain. I still have the alternator in there - seems have to remove it to access the dipstick tube.
Can't recall for sure, but thought the 27mm nut of the upper dipstick tube was still accessible from sort of underneath the alternator from the forward-facing side of the engine when under the car. Since you are not removing the (usually bent) lower dipstick tube that should make things easier .
Was trying again since not wanting to get into dipstick tube right now. Was able to lift cam, move to right, rotate a bit and clear the dipstick tube. Thanks for the quick comments back.
I measured all the shims again and was wondering how close I can get to nominal clearance since they only make in 0.05 mm increments. I found the handy valve clearance spreadsheet in the forum and input my values. Ends up I am able to swap a bunch and some don't need a change. However, I need the following shim thickness': 3.80 mm qty 1 3.90 mm qty 2 4.00 mm qty 1 Just wondering if anyone has these sizes available.
Plugzit is in Redondo Beach. Ping him he might have. Dealers might have. Mail order ricambi or gt car parts or sundry others. There are a few local Indy shop who might sell a few shims
Just wanted to mention that it's OK to reuse a valve shim, but only if it has a (fresh) surface that has never been in contact with the cam lobe before. When in contact with the cam lobe, the surface of the shim gets work-hardened so it can't "adapt" to another (different) cam lobe like a fresh (previously unused) cam shim surface can.
