Need Valve Train Help - 425

J

JZRIV

Member
I am rebuilding a 66 425 and am working on the heads. The guide clearances are in spec as well as valve stem diameters on the original valves.

The valve guides look original. Any sure 100% way to tell if they have been replaced?

The rocker shafts are worn on the bottom to where there is a noticeable step at the edge where the rocker pivots. The original aluminum rockers are worn about .010 on the diameter. How bad is that?

This engine might see 10,000 miles in the next 15 years at best. What is my best route? I don't mind spending money if its necessary but I am one who doesn't spend it "just beacuse" and like to have facts to back it up.

Here is what I am considering;
1. Buy new rocker shafts and reuse the original rockers as-is
2. Buy new rocker shafts and steel reproduction rocker arms? Are these steel rockers any good? CARS has them for $210 set.
3. Buy rebuilt shaft assemblies with bronze bushed rocker arms for $400.
4. Open for other suggestions

I am also trying to determine if the valve seats have ever been cut in the heads. The stem heights are running about .030 over the shop manual spec of 1.540. That makes me think they have been cut but since this is my first nailhead rebuild, I'm not sure the spec in the book is correct as the manual has been in error before. If someone could confirm from experience either way I would appreciate it.

Thanks in advance for any help.
 
In my experience any of the guides that are available today are JUNK!!!!. If they have been in there for 40+ years & haven't moved LEAVE THEM ALONE!!!! I have rocker shafts in stock that I make a small mod on for better oiling for "My Rockers" as well as the stock rocker arms. DON'T use the iron/steel rockers. They increase valve train weight & hence add extra stresses to the valve springs which is NOT needed or Nec. in my opinion, especially in a stock situation. The replacement "Repro" rockers are also JUNK!!!!! Use the originals whenever possible. The bushing in the rocker takes material away from the area that is MOST important for strength. I have many used rockers that are in good enough condition to be re-used. Specs on installed height are 1.540"-1.590". You could go as much as 1.630" but may need adjustable pushrods or custom length pushrods to get your lifter pre-load correct. One other reason I designed the Variable Ratio, Adjustable Roller Tip Rocker Arms. Right now on one of our engines we have an installed height of 1.750" & have the option of going to 1.900" when the proper valve springs become available, if ever. This also depends on the type of head gasket you will be using. Shim steel originals are about .015"-.016" compressed. Whereas the composites (included in most ALL gasket sets) are about .036"-.040" compressed. This brings the head "UP" higher with a resultant loss of compression to about .44 lower. Even the stock rating of 10.25 was very conserative. The pistons normally sit in the "Hole" about .040"-.050" below the deck. They usually fall into the area of around 9.6-9.7 originally from the factory. With the "Pent Roof" combustion chamber design we can run up to about 10-1 with today's fuel. With one finger I could type ALL night & not have given you enough info.

Tom T.
 
Tom,
Thanks so much for the detailed response. I was concerned about the extra weight of steel rocker arms and you substantiated that. Figured there was a reason they used aluminum to begin with. I will email you soon off the forum to check on new shafts and original arms.

It sounds like I'm OK with the 1.570 stem height then. Was it normal for stock stem heights to be anywhere in the .050 range you mentioned or was the factory more consistent and kept them towards the 1.540 min spec?

Thanks
 
I have NEVER had the opportunity to pull apart original, unused virgin heads. But, in my experiences, again, I have seen them off by as much as .030"-.040" higher between installed heights on the same head from a fairly low mileage engine. But they are usuallly pretty close.

Tom T.
 
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