Dear Friends, My friend Martin has his yellow gt4 and is doing a valve adjustment, water pump and timing belt change. I told him that if i had it to do over again I would have plugged my camshafts when I had them out. He ordered the correct plug from gt car parts and a set of the durable cam seals, to have both just in case. He had to leave on business for a few days and asked me if i would post this as he has a dilemma and was hoping that when he got back maybe someone would have some suggestions. The durable plugs he said when installed in the cam shaft are the same size as the spline drive assembly so when inserted there is no room for the spline drive???? The Ferrari parts from gt car parts are 20 thousands of an inch to big in diameter so he is considering having his spline drive machined out so that they will fit. I was hoping that one of you that have done this proceedure would offer some support or suggestions. I thought that the aluminum plug seals were just somehow tapped in the cam shafts and the spline drives were inserted after them but I guess I was wrong. We both have the FNA bulliten and it is as usual not as descriptive as one would like. I would like to do this myself some day so any help would be appreciated. I have been away for awhile as I am still recovering from a FCA event last spring, my car has not been the same since, we were taken on gravel roads and crossed 4 rivers, I will never do that again..............trust is a hard thing to come by......(Kurt Russel in "The Thing") Here is a picture of Martin's car he calls it Tweety, he is a good guy so please chip in, Rob Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
Rob -- The "plug" from durable1 REQUIRES removal of the stock distributor drive coupling so really is only useful when also going to another type of ignition system (Kermit should clarify that point). I must tell you that you're wrong when you say that the installation information is not given in TB N321 -- it clearly says "fit" -- which means (or used to mean ) that you machine the Aluminum plug down to match the bore of each splined coupling (since the splined coupling was not originally designed with a tight tolerance for that bore, they couldn't make a plug that work in all cases just in the as-supplied condition). Rework the (soft, non-structural) plug, not the (hardened and structural) splined coupling.
I have the Norwood ignition conversion which eliminates one distributor. Norwoods suggestion to grind down their supplied softplug and weld or epoxy it in place seemed a little "iffy", so i purchased Kermit's nifty cam plug. The po had given me a couple of the aluminum plugs but i liked the idea of a roll pin secured cup seal. I got the conversion up and running with an MSD6AL - sweet. So I pulled the back valve cover to do the plug and couldn't even find the roll pin that secures the cam drive to the cam. The pdf shows the cam cross section, what it doesn't show is that the roll pin securing the spline drive to the cam is located in cam support bearing. The factory appears to have gotten around this time bomb by making the pin god awfull tight. I tried to remove the drive pin by loosening up the cam bearing cap nuts to let the cam come up off its bearing enough so that the pin might be driven out, just above the surface of the cam bearing mount. It is necessary to pull the cam cap mounting studs to get a shot at the pin. I couldn't even get the roll pin out of the camshaft. it is so tight, i was afraid to tap any harder for fear of breaking the cam. I could see no way to get any kind of puller or press on it while it was in the car and have decided to wait for the belt replacement this winter to pull the cam so i can drive out the pin and fit the plug. I will use kermit's plug on the unused back cam and try the aluminum plug on the front cam. chris
Steve, That is what I thought, It would seem that since the aluminum is softer than the spline shaft an the part would be a tapered plug that could be tapped in place, however I looks like it has to have a hole drilled for the roll pin also. I assume you would turn the plug down on a lathe, It still seems strange to me, since you are not plugging the cam shaft oil could still leak around the spline drive perimeter where it is inserted in the cam shaft and still come out, even if the drive was properly sealed?? On a side note I have been just using the o-ring and it was a very slim affair I could never figure out what size it was, well I am working on getting my sun machine rolling and wanted a bunch of distributor o-rings so I ordered some from several different sources and they all seem to be much thicket than the original ones I was using for the last ten years? I am concerned that the too thick of one will roll on installation and cause premature failure. Does anyone know the actual size and composition of the correct o-ring size so I can but them in bulk? Thanks, Rob
I agree with you that a good leak-tight seal at the plug would seem best (I'd opt for a few tenths of an interference press-fit, if possible, and use a Loctite 518-type sealant whether a press-fit or slip-fit), but it could be that the plug's primary goal is more to ensure that, if the o-ring does fail, you just don't lose all of the engine oil so quickly (rather than trying to take the o-ring out of the picture completely seal-wise -- i.e., you can note that the TB doesn't say to not use an o-ring). If you can you measure the OD of the o-ring groove in the distributor shaft and the ID of the bore in the splined-coupling where the o-ring contacts I think you could deduce the right "ID mm x cross-section mm" o-ring (I'd be very surprised if it wasn't a standard metric o-ring).
Should the plug be tapered to sip in easier, I also assume that a hole must be drilled to faciltate the roll pin. Martin said he had quite a time removing the pin and had to drill it out!
Robert, Is is possible that the plug sits inboard of the splined drive?? My guess is thatthe plug needs to be "fitted" tapped im place then the cam drive goes back in and the roll pin is reinserted to secure the drive. dazed and confused - again, chris
Can someone explain what the purpose of this plug your discusing is? Did you put on a different ignition and you're trying to remove the dist. and put a plug into the end of the cam to seal it up?
Sean, The early 308's had hollow camshafts if the o-ring breaks the oil will spray out the distributor at 80 psi. It is thought the wise thing to do is remove the camshaft at a major service and plug the part that sticcks in the end and drives the distributor with a aluminum plug (see pdf in my first post). My friend Martin said that he had a terrible time removing the spline drive from the shaft and had to use a mill to get the pin holding the drive out. He said if he knew what he knows now he would not have attempted this as it is too easy to mess up the whole shebang. Of course :-( I suggested it as I always wanted to do it. If anyone has any experience doing this now would be the time to speak up. Chris the plug goes inside the drive as it is hollw also. Seems it would be easier to plug the camshaft..........but hey thats why we love Ferrari's!!! Rob Martin said he will post some pics when he is done
Well I finally installed cam plugs into the distributor drives. The factory plugs were about .020" bigger in diameter than the hole that they are supposed to press into. And that simply wont work. So I had a local shop custom machine two plugs from a piece of aluminum. Same basic configuration as the factory plugs. Because there was a variation in hole size between the two distributor drives (.461" and .460") each plug was custom machined to size to achieve an exact .001" interference or press fit. I then smeared some "Yamabond" sealant in the holes (seals the tool marks left behing by the distributor spline broaching operation) and used a large abor press to press in the plugs. There was a surprising amount of resistance. Those plugs are in there to stay. They would not have been able to have been hammered in. It simply would have mushroomed teh plug about 1/4 of the way in. I then hand drilled the 7/32" holes for the cross pins into the plugs, about half way in from both sides to allign, and then all the way through. Finally I heated up the end of the cams with a propane torch, and with a block of wood hammered the distributor drive assemblies onto the cam, being carefull to allign the cross pin holes. The factory cross pins followed (also hammered in) and the ends peened and mushroomed with a punch. You have to be extra carefull not to damge the cam bearing surface when doing this. So all this was completed successfully. But when you look at all the work and aggravation the end result,- an extra seal so that the O-ring seal on the distributor shaft is not "loaded", it simply is not worth the effort of a DIY retrofit, even if it follows the factory upgrade bulletin. There are also way to many opertunities for things to go wrong and damaging the camshafts. It is much easier to (periodically) change out the little O ring on the distributor shaft. Martin Jansen 75 308 GT4, Agoura Hills , So Cal.
Sounds like I am a bit late to the party, but we did the plugs in the cams. Machine shop. $70 incl materials in 2002. Later cars (79 on I think) had the plugs from the factory. Philip
Alternatively, you could replace the whole ignition system with an electromotive system (distributorless system) and silver solder US dimes over the ends of the cams (as my father did on his 308gt4) for a very tidy installation that's absolutely sure not to leak. You get the benefit of a much better/modern ignition system with no need to pay $700 for caps and rotors every 2 years.
