PDA

View Full Version : Valve Clearance on 351


Laurel_Lake_Skier
04-07-2008, 09:53 PM
I'm in need of some info on checking valve clearance on my 351. Along with a new intake, I just replaced the stock heads with some GT40-p heads. The heads are new castings so nothing has been shaved off as would have been on rebuilt heads. The engine is nearly together (I need to bend a new fuel line) and I want to make the tappet clearance check before starting the engine which hasn’t been run since last fall.

I have a couple of problems. First off, I have three different sources giving three different specs. My Indmar manual lists the gap at 0.123-0.173 after collapsing the lifters but it shows a picture of a feeler gauge with a single blade between the rocker arm and valve stem......Another manual lists the compressed clearance at 0.060 and an instruction sheet that came with the set of shims I bought just in case I had to make adjustments lists 0.020-0.060 as the correct clearance.

I tried making my own lever-type tool to push back on the rocker arm and collapse the lifter (I had the cylinders at TDC on compression) without much luck. The handle is about 14 inches long and I could feel the lifters compress a very slight bit but I have nowhere near the Indmar spec (clearance is 0.020-0.030)....... How hard should it be to compress the lifters? How long is the handle on the “tappet bleed down wrench”? Is there another tool/method other than the bleed down wrench that will work to compress the lifters?

Any insight is appreciated.

rcnjson
04-08-2008, 01:51 PM
L_L_S,

I would take a step back before you set the rocker arms. If you replaced your heads, you have probably changed the push rod / rocker geometry. I think the first step would be to check your push rod length. That is not to say the engine won't run using the old push rods, although it may not, but you are certainly leaving some power on the table.

To check for proper push rod length with hydraulic lifters you will need the push rod checking tool and a solid lifter. The tool you buy the lifter you make. I made a solid lifter out of an old lifter that I wasn't going to run anymore, I pulled the retaining wire, pulled the plunger, pulled the guts (springs) out, replaced the springs with washers and replaced the plunger and retaining wire. Then you use the lifter with the push rod checker to get the geometry correct and then you can measure the checker to determine what length push rods you need. If the push rods you have are the same length as what you measured you can continue with setting the rockers if you need a different length, you need to buy those first.

Once you have the correct push rods, you can set the rockers. For Pedistal mount rockers (you have this type if you are talking about shimming) this is how I do it:
To install pedestal mount rockers:

1) For each pair (int/exh) be sure you rotate the engine so the lifters are on the base circle of the cam - this is very important. When you install the rockers, both valves must remain closed. Neither lifter can be on any part of the cam lobe - they MUST be on the base circle.
2) Remove the distributer and run the oil pump with a drill in reverse to pump up the lifters. Install the rocker and bolt it down to zero lash. Zero lash is reached just when you eliminate the gap between the pushrod and the rocker and the valve stem and the rocker. Tighten with one hand and 'rock' the rocker with the other hand. Just when you reach the point that you can't rock the rocker anymore you're at zero lash.
3) Now - put your torque wrench on it and tighten to 18-20 ft-lbs. while counting the number of turns it takes to reach that torque. It should occur between 1/4 turns and 1 turn. If it takes more than one turn, use a shim to raise the rocker. For each .030" shim you use, you'll reduce the number of turns to torque by about 1/4.
4) If all goes well on the install, crank it up. If some make noise let the car warm up completely. Then (unfortunately) go back through the install procedure with the components warm. That will usually quiet them down.

Laurel_Lake_Skier
04-08-2008, 05:38 PM
With what I've read, the "P" heads just have a different combustion chamber and spark plug location. The valve train geometry is supposed to remain the same between the two head types.

When making your solid lifter, did you base the number of washers on bringing the plunger up to the retaining wire groove? That seems to be the reverse of what the manual is telling me on applying pressure to bleed down the lifter and then measure clearance.

viabill
04-09-2008, 01:53 PM
Laurel Lake... You are correct. With the new Ford heads, you do not need to recheck the geometry. You don't even need to be concerned about piston to valve clearance since you did not mention anything about changing to a bigger camshaft.

You only need to follow standard valve adjustment procedures for Ford 351W or 302 engines built after 1980 (back in the 60's and 70's these engines had positive stop rockers (called bottleneck rockers) that only needed to be torqued down... no adjustment.)

Try Googleing 351W valve adjustment. Comp Cams has some good instructions on the web you can use for comparison.

rcnjson
04-09-2008, 01:54 PM
Yeah, I understand my method is the complete opposite, but it works. Here is the deal, if you check the push rod length and install the correct push rod then it is easiest to work with a lifter that is pumped up. You work to zero lash and the lifter pre load is then set when you torque the rocker arm.

As far as the home made lifter, I brought the plunger all the way up to the top. Again that way you are only dealing with pre load when you achieve your final torque setting and you can get everything set (push rod length, rocker / valve geometry).

I will offer this aside regarding the heads. The GT-40P's came from the factory on a 302 with a roller cam. Roller lifters ride higher in the lifter bores. So even on the same engine a 302 w/roller -vs- 302 non-roller, the push rod would need to be changed. Now we are talking about a 351w non-roller so my bet would be the push rod length is incorrect. Like I said before, the engine will probably run, but you are certainly leaving power on the table.

Jason

TRBenj
04-09-2008, 02:50 PM
I will offer this aside regarding the heads. The GT-40P's came from the factory on a 302 with a roller cam. Roller lifters ride higher in the lifter bores. So even on the same engine a 302 w/roller -vs- 302 non-roller, the push rod would need to be changed. Now we are talking about a 351w non-roller so my bet would be the push rod length is incorrect. Like I said before, the engine will probably run, but you are certainly leaving power on the table.
When going swapping from E7 to GT40p heads, it wont hurt to check pushrod length- but its not a given that you'll have to change them, especially if the P's are new castings. Dont confuse the issue with roller vs. flat tappet, 302 vs. 351- the valvetrain geometry is the same between the P's and E7's. You'll certainly want to set the proper lifter preload via shims regardless. LLS, just follow the comp cams instructions and you'll be fine.

Ive got a set of rebuilt P's on my 351w and I am running the stock pushrods. I promise that I am not leaving any power on the table!