Hi All, Just checking on cam timing marks for a 308 gt4. When I have cylinder #1 TDC and PM1-4 on the flywheel I have my camshaft marks lined up with the cam bearing cap marks on bank 1-4. Then when I look at the cylinder 5-8 bank the cam marks are 180 degrees from the cam bearing cap marks on this bank. Hope this makes sense, does this sound correct for base timing of the cam shafts? Would have posted some pics but had trouble posting them sorry. Cheers George
Was it running like this or did you change the belts or something? On my 308GTSi both the 1-4 & 5-8 cams are on the cam cap reference marks when #1 is tdc on compression stroke and lined up on PM 1-4.
YEP. Mine too. On my '81 GTSi. All 8 marks on the cams(4) and caps(4) pretty much line up with the PM 1-4 mark on the fly wheel. I am not even sure you can arrange the cams like the OP says and not have "valve meet piston" issues but do not quote me on that.
All the marks on all four cams should line up pretty close at number 1 TDC. They are assembly marks, and that is how they engine is assembled.
Is there any chance someone can post a picture of the cams in bank 5-8 when cylinder 1 is at TDC and the 1-4 bank cams line up with their cam bearing cap marks? If I can see how the lobes in bank 5-8 should be placed when cyl 1-4 cam marks are lined up then this will confirm if I have these cams in the right place. The cams are aftermarket performance items, not factory and have a red marks on them from original installation which lines up perfectly on the 5-8 bank cam caps when the 1-4 bank is set to Cyl 1 TDC, PM1-4. The reason for the work is due to an exhaust cam drive failure on the cyl 5-8 bank, with bent valves.
If the cams are truly 180 out (360 out at the crank) you won't crash valves but the distributor (rotor) would need to be 180 as well for the cylinders to fire and is possible. It would be an odd firing order and I imagine the engine would vibrate more or feel less balanced but it should be possible to run that way. I wouldn't recommend it though. All four cams marks should align within a few degrees of the cap mark. PM sent
A. Rotor cannot be installed 180 off B. Why would it vibrate? It is just 2 4cyl motors on a common block.
Remove the distributor from the cam/engine Hold body of distributor Grab rotor with other hand Spin rotor 180 degrees (rotor shaft will spin with it) Slide distributor back into cam shaft Not trying to be a smart *** just trying to help visualize it.
You don't need a picture -- just watch the order of action of the valves as you rotate the crankshaft in the direction of normal operation. For example, rotate the crankshaft until the #1 intake valve is fully open (#1 intake lobe pointing straight down pushing the bucket down to its lowest position), then rotate the crankshaft another 90 deg in the direction of normal operation, if things are right = the #5 intake valve should be fully open (i.e., the valve action should be following the proper firing order of 1-5-3-7-4-8-2-6); if things are wrong = the #8 intake valve would be fully open (and that would be the wacky firing order of 1-8-3-6-4-5-2-7). Yes, on the dual distributor models, it is possible to get this wrong as you described, and still have all cylinders fire and run, but it would vibrate a tad more than normal (because 1 and 8 are on the same side of the engine's cg; whereas, 1 and 5 are on opposite sides of the engine's cg), but the bigger negative is that having the two cylinders on the same crank pin fire adjacently = about doubles the instantaneous load on the nearby main bearings = not a good thing...
Thanks Steve, this is the information I am looking for. The CAMS are not factory items, they are after market long duration cams. I can't be sure the marks on these aftermarket cams are set up the same as factory cams, I believe I have the cam timing correct as there are some red marks that line up on both of the 5-8 cams and cam caps that lined up (at least on the 5-8 inlet cam) before I removed the 5-8 head for repair. Repair was required as the 5-8 exhaust cam pulley failed, the cam stopped but the motor and other 3 cams kept going. Result was 4 x bent cylinder 5-8 exhaust valves and 2 bent 5-8 inlet valves. All valves have been replaced and the head and cams have been checked for damage/cracks. I'm away from home at the moment so I can't verify what is happening 90 deg after Cyl 1-4 TDC but will in the next day or so. The engine does not use distributors, it has coil packs and fuel injection managed by a haltek ECU.
It sounds like someone set up the alignment marks on the new cams so 5_8 was at the cap mark when #5 was at TDC. The factory cams have all marks lined up when #1 is at TDC.
No. When 1 was at TDC overlap instead of TDC compression. We used to see it all the time when 308 servicing was still a big part of the business. The running is indiscernible from a properly set up motor.
Can't you just compare your new cams to the old ones, surely only the profile has changed. Can't imagine any aftermarket manufacturer actually changing the firing order. Regards Bell
Yes that would make it easier, but I don't have the old cams. Oh and also the flywheel and clutch are aftermarket so no factory marks on them, just paint marks from the previous engine builder all of which i have verified using the piston stop method.
Using Steve Magnuson's method of checking that the intake lobes follow the firing order i can confirm that i have installed the cams correctly. The manufacturer of the cams had marked the cyl 5-8 bank cams 180 degrees out.
