I've run into valve issues on my truck's 69 302 that I'm rebuilding. I'm hoping you guys can answer a few questions for me. Hopefully you're not getting sick of me asking questions...I know I'm getting sick of asking them!

Can anybody tell me if the valve seats are at different heights within the heads? My valve stems are different heights intake/exhaust and I'm beginning to think that the machine shop might have put in valves with longer stems than stock. Anybody know a way to measure them without pulling the heads and then pulling the valves themselves?

Alternatively, does anybody know how much forgiveness a lifter will give you? Obviously I'm beyond that amount, but according to my engine manual I'm close...maybe just one pushrod step away. Thanks.

I've got less than two weeks to get this sorted out.

Thanks in advance,
Jim

 

Normally the machine shop runs the head (with all valves installed) thru a mill to equalize all the stem heights as a last step. Should be easy to measure with a caliper.

 

Sitting on my block, with the rockers pulled, the valve stems are pretty even...with intakes running +/-.030 taller than the exhaust.

I'm having problems with the new valves the shop installed staying open. They did new valves, seats, and springs and now stuff's all out of whack. I've double and triple checked everything from the timing set, to the distributor drop; searched for vacuum leaks, and even had a chat with Melling about the new cam to see if it was causing the problems. Everything checks out...except the valves...and unfortunately the guys at the machine shop had left for the day by the time I got to this point. If I can I'll get the part number for the valves they installed, but that still might not get me anywhere.

At this point I don't know if changing pushrods would be the right answer. Shorter pushrods might keep the valves from staying open, but might change the geometry and cause problems.

Thanks for the reply though.

Peace,
Jim

 

It seems to me I bought a "pioneer brand" set of nuts with set screws to make the 302 adjustable once.I believe all the hp versions were adjustable with screw in studs only.Yes they are different lengths.

 

After a conversation on the phone with a mechanic, the valve stems are supposed to be ground to the same length. The base circle on the cam is the same for intake and exhaust valves, so there's no reason for different lengths, and if they're not the right length (within a few thousands which the lifters can accommodate for) it'll cause problems. Right now the intake valves are close to the same, and the exhaust valves are close to the same, but between the two is .030+/- difference. It just wasn't done right.

Now I have to pull the heads (intake and exhaust too) take them down and convince them to fix it and give me new gaskets for free. I'm not looking forward to that.

Jim

P.S.>>>I've read stories of guys who tried to make adjustable studs out of these 5/16th studs and had them break off running down the highway. The adjustable studs were 3/8ths studs. Set nuts might be worth looking into before I tear everything apart.

 

I have never played with the stock parts but I think there are a couple or three lengths to correct this.That pioneer set was pretty reasonable if I remember right.

 

I don't think the rocker geometry will be correct unless the valve stems are the right length.

 

If I am reading one of your posts correctly, you think some of the valves are not closing all the way? If that is the case, a compression tester would confirm it as you would get no compression on a cylinder with a valve not closing.

 

dmack,
You've got it right. Valves aren't closing. The machine shop said not to torque them to spec, but to set them like adjustables. Their reasoning was two fold: a) the new, bigger cam caused this, and b) they had another 69 302 out of a mustang they did the same time as my motor and it ran great that way. So, with doubts, I lashed the valves as adjustable. When I did that I got 140psi on my compression test, but the rocker nuts wouldn't stay where I left them...reason being that 5/16ths rocker nuts are NOT self locking like the 3/8th stud's rocker nuts.

I had a little chat with Melling's tech service and they confirmed that the new cam (made by Melling) has the same base circle diameter as the stock cam, and it's the same for intake and exhaust lobes. Therefore all stock length lifters, pushrods, and valves are intended to be used with the cam I got. I know I've got the stock style lifters. I'm using the original rockers and pushrods. And I know the intake and exhaust valve stems are different heights. We'll see what the machine shop has to say today.

 

That pioneer kit is nuts with set screws so you can set and lock them in place.I think crane makes them as well.It was made to work with stock rockers,any local speed shop should stock them.Makes your stock set up adjustable.

 

If you go into garage sale items at speedway motors there is a set for 7/16 studs,I don't think these are right for you but check it out.The style nut you need to replace stock setup."Mr. gasket ford sure lock rocker arm nut"It will make your life easy.

 

Went to the shop this morning. They tossed out the idea of poly-locks, which they are sure they can get in 5/16ths. The question is, will the geometry be right? They gave me some Russian Blue to test and on the exhaust valves it looks fine, but on the taller intake valves there's very little margin between the top end of the valve stem and the top end of the rocker contact.

I don't know what the tolerances there would be. Anybody got an idea there?

Jim

 

Someone correct me if I am wrong but ford's three different height rods will correct this problem.Sounds like a shorter rod should "square this up".If your valves are hanging open.I think they come in 30,60 and std lengths.Longer or shorter I don't remember.

 

Jim,

I'll have to go down to my workshop and check a manual, but I have done a couple of non-adjustable 302's and the 351w in my F1. The assembly procedure calls for putting each cylinder in the firing position and with dry lifters, rocking the rocker back (with your fingers) to see what gap is there between the rocker and tip of the valve. The spec is really fat...like .100 or more. The lifter will take up all of this and more. If the gap is too tight, they tell you to put in a shorter push rod.

I don't think that the valves being 0.030 higher will change the geometry enough to cause a problem...other than you may have not enough gap or no gap at all, so the valves aren't closing. Higher than normal valves along with a little deck grinding on your heads may require some adjustment.

Here is a Melling spec sheet: http://www.melling.com/LinkClick.asp...U%3d&tabid=702

Use this with the application guide at Summit Racing or Jegs to find shorter push rods if you need them. The Summit listings don't state the length, so you'll need some other reference to see what length each part number is.

Since your lifters aren't dry, you'll need a lever to bleed down the lifter to see what gap is there...with some force, a lifter will bleed down slowly, so be patient when you do the check (patient yet forceful). Bleed-down tests on lifters are done with oily solvent in the lifter, so with motor oil in there, it will take some effort.

Dan

 

Ol,
Thanks for the leads. I've done some searching and found poly-loks from Crane, Pioneer, Comp Cams, and Mr. Gasket...the latter being the most affordable.

The Machinist says that the margin on the valve stem tip is good and that poly-loks won't cause a problem with the geometry. So I should be able to use the same push rods, and with the poly-loks I can set the rockers like they're adjustable and I should be good to go...and at no cost to me.

Dan,
An alternative in my engine manual is to set the valve to zero lash and then count the rotations to the positive stop. Between 3/4 turn and 1 & 3/4 turn is supposed to be within spec. My rockers tighten down 2 & 1/4 to 3 & 1/2 turns after zero lash. Last night I measured the vertical distance traveled for 1/4, 1/2, and 3/4 turns; roughly .010, .020, and .030 respectively. If you lash your valves 3/4 turn from zero lash, that gets me between .060 and .110 too long. According to the Machine shop the lifters have .150 travel, so that leaves .040 travel left (assuming my rough figures are accurate). But once the rockers are down on their stops, there's no gap between the rocker tip and the valve stem tip...nothing at all.

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It occurs to me though that all of this is something of a moot point. The motor had original valves, rockers, pushrods, lifters, and cam. The rockers were torqued down to the positive stop and it didn't have compression problems 15yrs ago when I got it. Now it has original rockers and pushrods, and stock lifters and stock BC cam. The valves are the only difference and they're hanging open when the rockers are torqued down to the positive stop.

Shorter pushrods would be one option, but I'm thinking they'd take the geometry further out of spec, rather than bringing it closer. Grinding the valve stems down to the same height as the originals would correct the geometry, but that'd require me pulling the carb, intake, exhaust, and heads; waiting on the machine shop to get the job done, then re-installing said pieces and then hoping they did it right.

At this point that's just not very appealing for a guy with no pnuematics and a 12 day deadline.

Raising the fulcrum (the pivot point of the rocker) is the solution that adjustable rockers use for this problem. If the poly-locks will give me that, it might actually improve the geometry (with the long valve stems) and I know for a fact the engine will run well with the rockers adjusted out. (They just wouldn't stay that way without locking nuts) Having tested the contact patch between the rocker tip and the valve stem with the rocker torqued I don't think I need longer pushrods too.

Not to mention it's about a 30min fix which is appealing I have to admit...just being honest.

Jim