lifter preload
- Thread starter gsbuick65
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turbofabricator
Well-Known Member
- Joined
- Mar 7, 2004
.032" of pre-load is ideal. Next time, instead of buying new pushrods, you can just install .016" or .032" washers under the rocker shafts. Real cheap way to adjust pre-load. Just stack them as needed to get the pre-load right. Roller rockers are even easier, and a better way, too. There are alot of Buick engines running today that have up to 100 hp hidden in lifter pre-load. If you have .090" or greater, the engine will be WAY down on power. The above post was correct, in that .020"-.060" id target pre-load. I shoot for .030". I adjusted pre-load on a virgin 30,000 mile stocker many years ago and he picked up 3 mph at the track, with all else being the same. Even from the factory, the pre-load is off on many cars. Production tolerances.
johnnyttype
Active Member
- Joined
- Apr 18, 2007
hi, i was just wondering if it is possible to check preload without pulling the intake off and what tools you would need to do so? i was just wondering what mine is if you have .090".
turbodave231
Moderator
- Joined
- May 24, 2001
I don't think shims under the rocker shafts is a great way to adjust preload. Yes it will work, but it will also cause unwanted geometry problems between the tip of the rocker and the valve tip. This will side load the valve and cause guide wear.
One of the problems is incorrect valve installed height. Grinding valves and seats causes the valve installed height to change (grow). This adds to the lifter preload. The tips of the valves can be ground about .020 to adjust. After that the valve or seat needs replacement to restore valve installed height.
Decking the block or milling the head also adds to lifter preload. If valve installed height is correct, and lifter preload is still a problem, it should be corrected with different length pushrods. This keeps the rocker/valve tip geometry correct.
One of the problems is incorrect valve installed height. Grinding valves and seats causes the valve installed height to change (grow). This adds to the lifter preload. The tips of the valves can be ground about .020 to adjust. After that the valve or seat needs replacement to restore valve installed height.
Decking the block or milling the head also adds to lifter preload. If valve installed height is correct, and lifter preload is still a problem, it should be corrected with different length pushrods. This keeps the rocker/valve tip geometry correct.
IT would be hard, but you could get a pushrod checker (adjustable pushrod)and adjust it where you just have drag on it. that would be zero, get a pushrod ..040 longer.
Thats exactly what you would do and its not very hard either. Just be sure your on the base circle of the cam when checking the length. Then just get a set of pushrods that are .030in longer +or-.010in.
turbodave231
Moderator
- Joined
- May 24, 2001
You can buy pushrod length checkers from Diamond Piston's sister company Trend Products ( and lots of other cam vendors too). The checker is a threaded 2 piece pushrod that extends .050 for every full turn. They are easy to use, accurate and fast. A full set of custom pushrods costs less than $100
This beats shimming the rocker shaft and keeps your geometry correct. I'd be very hesitant to shim the rocker shafts. I've seen problems breaking rocker shafts and that shim can't give proper support to the shaft.
Here is a great article to read on valvetrain geometry and how to check for the correct length pushrod
A Pushrod Length & Rocker Arm Geometry "Must Read"
This beats shimming the rocker shaft and keeps your geometry correct. I'd be very hesitant to shim the rocker shafts. I've seen problems breaking rocker shafts and that shim can't give proper support to the shaft.
Here is a great article to read on valvetrain geometry and how to check for the correct length pushrod
A Pushrod Length & Rocker Arm Geometry "Must Read"
johnnyttype
Active Member
- Joined
- Apr 18, 2007
Cool, i actually have a pushrod length checker from Crane and i just ordered a slide caliper so i could measure the checker.
I suggest you go to COMP Cams - Performance Camshafts, Valve Train, & Much More and read their tech info on how to measure a pushrod (or pushrod checker) to make sure you get the length you think you will.
ESP Products
Banned
- Joined
- Feb 27, 2002
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I agree. You also run the risk of cracking/breaking your rocker arm mounts. These cast pedistals are sized exactly for the rocker shafts. If you add shims you run the risk of side stress and you can break the mount. Spend the time and look up the proper size rod length(s); we do it all the time.
Hope this helps you.
I have to disagree with the statement that raising the pedistal with a shim method should never be used. The shim material must be quality material that is hard, and perfectly flat. With that said, putting a washer under it is not advisable. The correct geometry must be verified, which tends to limit the amount you can raise the pedistal to around .015-.020 in. My point is this. It can be used, if done correctly, with reliable results.
Danny
Danny
turbodave231
Moderator
- Joined
- May 24, 2001
I personally would never do anything to intentionally move the geometry in the wrong direction. IMO, Shimming the rocker shafts is a bandaid fix to correct a bigger problem.
I've never seen a curved, hardened shim, .015-.020 thick? The shim would have to go between the saddle in the pedestal and the round shaft!! I don't think the rocker shaft can sit in full contact in a half round pedestal bore with a piece of .020 shim stock in between. Think about it! The shim reduces the "diameter" of the saddle by double the thickness of the shim. The clamp load exerted on the pedestal by the shaft and shim would want to crack the pedestal.
Dave
Dave, you burned me man! Bandaid is a very good way to describe what I was talking about. If I was building an engine, that method would not be used. I don't like to cut the valve tips unless there is no other option. Maybe instead of band aid, we could call cutting valve tips an antiseptic spray or ointment for a bigger problem. Ha ha! I should not have started my reply with "I have to disagree". I am sorry for that, and I would have no problem at all trusting you to build my Buick's engine if I became unable to do so myself.
Danny
Danny
Crammysauce!
New Member
- Joined
- Feb 23, 2007
So, I read the reccomended Comp Cams tutorial. Is it seriously just a matter of looking at the valve tip surface contact area, and making sure that it's hitting the required front middle and back? I've never had to do this before, so if someone can spell it out, that would be great. I have ordered a pushrod length checker already.
Edit: Is the "base circle" the valve tip surface, or a specific part of that surface? Thanks again!
Crammysauce!
New Member
- Joined
- Feb 23, 2007
Great - that makes much better sense. Thanks for the reply!
Lee Thompson
New Member
- Joined
- May 24, 2001
With shaft mounted rockers
As our Buicks have, the only way to change the geometry is to raise or lower the shaft. I tried to shim the shaft ONCE--broke the pedestal as I am an idiot sometimes. After breaking the shaft it dawned on me that the shim would need to be tapered as Dave said. Com Cams catalog leads you to believe by changing pushrod lenght you can change the geometry and you can if you have individual rockers as a Chevy does. Best of luck.
As our Buicks have, the only way to change the geometry is to raise or lower the shaft. I tried to shim the shaft ONCE--broke the pedestal as I am an idiot sometimes. After breaking the shaft it dawned on me that the shim would need to be tapered as Dave said. Com Cams catalog leads you to believe by changing pushrod lenght you can change the geometry and you can if you have individual rockers as a Chevy does. Best of luck.
