Head Pins

**smestas** · #1 (**permalink**) 07-08-2005, 01:21 AM

Has anyone here ever seen head pins like this?

**smestas** · #2 (**permalink**) 07-08-2005, 01:22 AM

Here's another shot.

Jim K. · #3 (**permalink**) 07-08-2005, 07:55 AM

No, and they're probably too darn small! Whats on the head side?
Jim K.

73gtv · #4 (**permalink**) 07-08-2005, 10:48 AM

These look more like restrictors for oil flow control to the head to increase supply to the mains.

**smestas** · #5 (**permalink**) 07-08-2005, 11:41 AM

Quote:

Originally Posted by Jim K.

No, and they're probably too darn small! Whats on the head side?

**GTV4EVR** · #6 (**permalink**) 07-08-2005, 12:07 PM

I couldn't find the thread quickly, but this was discussed a while back. Someone was selling roll pin replacements designed to restrict oil flow to the head.

dwc · #7 (**permalink**) 07-08-2005, 01:47 PM

I can't comment on the benefits or disadvantages of restricting the oil flow to the cams, but the pins do serve another function, which seems to be missing from what's pictured. They hold the o-rings in position, which is why Alfa began installing the pins in the 2-liter engines back in the mid-'70's. There are several options available, although I'm partial to the type sold by Alfa Parts (Jon Norman). Avoid the ones sold by IAP, which are split pins with razor-sharp edges, as they will cut the o-rings (first-hand experience). Not sure why a vendor would sell such a thing.

Dean
Lutz, FL
"74 & '87 Spider Veloce's

**italcarguy** · #8 (**permalink**) 07-08-2005, 10:16 PM

I spoke with the OS Giken guys today and they did this to give the bearings more oil. The hole is big enough to where the cams get enough oil, and still give more oil to the bearings.

Jim K. · #9 (**permalink**) 07-09-2005, 06:33 AM

Thats great, there's actually someone who knows exactly the bearing and cam oil quantity requirements, in order to come up with the proper size restrictors...not bad!

Experimentation never hurt nobody anyway.
Jim K.

**smestas** · #10 (**permalink**) 07-09-2005, 01:22 PM

Quote:

Originally Posted by Jim K.

Thats great, there's actually someone who knows exactly the bearing and cam oil quantity requirements, in order to come up with the proper size restrictors...not bad!

Experimentation never hurt nobody anyway.
Jim K.

Jim K. · #11 (**permalink**) 07-09-2005, 04:30 PM

Alfa always prescribed oil pressure limits with a hot engine, but never flow.
It would make for a very interesting experiment to try and find out. One would require a decent size drill press turning at about 2500rpm, some means to immobilize the pump on it, about 2-3gallons of HOT oil and a means to connect pump output to a restrictor and a mechanical pressure gauge. You would then start the drill and adjust the restrictor so the gauge reads about 60psi. Stop there, return all HOT oil just expelled to the container and restart, this time with a stopwatch. Run for, say 5-10 seconds and stop everything. Measure how much oil left the restrictor and there's your flow! Its all nice and dandy talking about it, that HOT oil (100*C or 212*F) is what makes things difficult! Anyone out there interested AND brave enough ? Not that this knowledge is worth anything, but what the hell! (It may actually help someone looking to dry-sump their pet!)
Jim K.

Greg Gordon · #12 (**permalink**) 07-09-2005, 04:43 PM

I don't understand what's going to hold the o-ring in place.

**GTV4EVR** · #13 (**permalink**) 07-09-2005, 06:28 PM

The O rings stayed in place (usually) without roll pins for years!. My 1750s never had them. Shouldn't the head gasket be enough?

**italcarguy** · #14 (**permalink**) 07-11-2005, 10:48 AM

I spoke with the OS Giken techs this weekend and they said they haven't had any issues with this moditication. As for the o ring, it fits in the opening in the head gasket and doesn't move when the head is in place.

vsharp · #15 (**permalink**) 07-12-2005, 06:31 PM

If you crunch the numbers, working on the factory cam bearing clearance of .0016" or .04mm, you can work out that each cam bearing has a bleed off gap area of 3.1sqmm per end (6.3 per bearing, or 18.9 for all three ). A single stock 4.75mm feed hole (no roll-pin) has a supply area of 17.7sqmm....ie you could feed all three bearings with virtually no pressure loss at the cam bearings with just this one hole. Of course you don't actually need full oil pressure at the cam bearings, because the the loadings, surface speeds and heat generated here are minimal compared to the bottom end bearings, (these are what the oil pressure/ flow requirements are designed around.)
If you now take the T/S motor and look at it's cam oiling, you will find one feed hole with a roll-pin and a hole size of 3mm dia/ 7sqmm area, at the front bearing only, (the others are fed by this via a drilling along the head) . So a T/S can supply both the cam and the variable timing device with just a single 3mm hole. Obviously the three 4+mm holes per cam in 105 type motor is not necessary. If you use 1.75mm as an option for instance, three holes of this size works out to 7.2sqmm, or about the same as a T/S, and we know this works.
I would however be a bit more generous on a turbo engine where a lot of heat is generated, especially on the exhaust side, because the cam oil also feeds the lobes and buckets and cools the valve springs.
The other hole that can be restricted is the intermediate idler sprocket feed. This can be reduced to 1mm dia.
VS