Oh great.. I`m putting in 2 new Clay Smith pumps and now I have to worry about the pushrod?

Tom,

The fuel pump pushrod, like the distributor gear, must be matched to the core material.

Am I correct, you are running a Crane Cam (copper colored between the lobes)? If so it is a carburized 8620 core and requires a compatible material for the pushrod. The Crane part # is 11985-1, available online.

Bob

Bob, what do you recommend for billet cores that you use? Same thing as for the Crane? I'm planning to run basically the same pump as the others are discussing.

I'm wondering if the stiffness of the spring in the pump is a factor in the pushrod tips mushrooming out. It would follow logic that the heavier spring puts a lot more pressure on the rod. I also came across someone discussing the two little "helper" springs that push the arm out to be in contact with the pushrod. Apparently if these are weak it could allow excessive play in the pushrod instead of holding it firmly on the cam lobe. If this happens then it would be easy to see if getting mushroomed out as it gets hammered by the lobe as it rotates. Anyone else encountered this?

Did the 800 and 900SC engines run a billet roller cam, or was it a cast core? If billet, what pushrod was Merc using?

i use the comp cams 4607 with no failure to date.the one bob posted is the same thing just crane,s version.

The 800sc used a flat tappet camshaft, and pushrod part #35377 , which listed for about 25 bucks.

The 900sc, used a solid roller camshaft, and pushrod part #848471, which listed for 66 bucks.

They both used fuel pump part #8M8024635 which listed for 270 bucks.

The fuel pump used on the 800sc, 900sc, was the above part number, but simply was a holley six valve self regulated pump. They still had the holley stamp on them. The 900sc was a 540ci, 8.0:1 static compression. It had a solid roller camshaft, brodix aluminum heads, 10-71 Mooneyham superchargers, LEE intercooler, with twin 1050 dominator carbs on top. It had a wot RPM range of 5600-6000RPM. They used a Thunderbolt capacitive discharge style igntion box on them.

The fuel system consisted of the fuel pump mounted on the block, then to a filter #35-848850A2, then split to the carbs. There was no regulator in the system, no electric pump, no return lines.

We run a pair of 900's with baker pumps. Anything over 5k rpm fuel pressure does drop off. Added electric fuel pumps with no regs and it maintains 12 psi with no issues. It's not a fuel supply issue, 5/8 supply lines with 1inch pickup tubes. If we didn't buy new pumps I would of bought a block off plates, reg, and Aeromarine A1000, no more thoughts of lack of fuel.

What carbs are you using that can take 12psi without flooding the engine?

While I personally have not had this issue, I have read about it, and want to mention. That is, that these mechanical style pumps can suffer from what they refer to as "cavitation" at high RPM. Hence the development of a lightweight carbon pushrod that weighs only 29 grams. I am guessing, that at high engine rpm, the pump spring can be too weak to keep up, and possibly a condition similar to valve float when an engine doesnt have enough valve spring pressure to control the valvetrain. I also guess that the lightweight pushrod, helps take some of the load off the pump return spring, allowing the pump arm to return to the closed position fully on each revolution, so that it can complete its next stroke in a complete manner. Not sure if I am explaining it properly.

http://www.competitionproducts.com/H.../#.VOvwqC7LpE4

Using a bronze-tipped Comp pushrod for one of of your cams, same p/n as used with my SBC cam from years before.