40K Elise: Changed My Lift Bolts /
By moremonkey’s Stan
I had a chance to pop my valve cover today. I wanted to look things over and check out my lift bolts. Here are some pictures and comments.
I can do a lift bolt changeover write-up if folks are interested. Basically they are a wear item in the cam changeover gizmo and sometimes they break. Once your valve cover is off (10 minutes or so, a trick or two but easy) they just unscrew and you load in the new ones. They cost me 98 cents for the two you need, one bolt per cam. The valve cover goes back on easily, there are a few things to line up, you need a dab of glop near the chain cover and you reuse the rubber gasket.
Here is the head with the valve cover yanked...clean as a whistle, synthetic oil baby.
Here is a closer view with the lift bolts unscrewed.
New versus old bolts...see the wear pattern? There is a ridge and the wear goes all the way around the bolt.
I am glad I changed the lift bolts. If the bolt breaks off it is a pricey repair and you can't hit the big cam in the mean time.
Underside view of the valve cover. Note the lubrication plumbing designed to aim at the high cam lobes and keep them alive.
A closer view; The tube lives in the corner near the trunk and oil fill cap.
Some high cam lobes have the ? appearance. No pitting or scratching if you test with a fingernail. Maybe that is some remaining coating (see lobe sides). Also note the roller VS slipper concepts. The low cam uses a low friction roller lifter...they are undemanding lubrication-wise due to the rolling and not sliding/rubbing action The high cam slipper sees very high rubbing loads, which requires some extreme pressure (EP) functionality from the oil. Note that such additives have been reduced several times as the API certifications SL, SM, etc have progressed. See: http://www.monkeytuner.com/forum/viewtopic.php?t=554. I'd want to use a proper oil to protect the high cam if I was on it a lot... The API has capped such additives because they suspect that catalytic converters will get coated in about 8-12 years of normal car mileage. Your converter still flows, it just cuts pollutants less. The additive issue is more of a concern for non-roller cams and for piston rings in certain cars.
Here is an overall view:
Our motor uses the lightweight shim under tappet approach. Little lash caps on top of the valve stems. The roller and slipper are height matched such that both clearances are set when the tip clearance is set. The wear is low, it's a PITA to set as the cams have to come out. But especially if you'll have the cams out reset it all. You check clearances with everything together, writing it all down. Then you disassemble the works and measure the shims, calculating what is needed. After doing any needed, you reassemble and confirm clearances. Some cars use pop out disc shaped shims weighing about an ounce apiece...which are much easer to service...but those weighty shims and their buckets affect high rev operation and required spring rates.
“Why are they called lift bolts?”
They are commonly known as
lift bolts by the Celica guys.
I've run mostly Mobil 1 0W40 oil, first in the API SM version, and subsequently in the latest SL version. Both API specs have reduced ZDDP compared to prior specifications. It also appears that some of the Mobil 1 weights are fully synthetic only in the legal sense. Now I'm running Mobil's (legal and actual 100% synth) Delvac 1 5W40 API SL for now along with a Mobil 1 #209 (larger than stock) oil filter Delvac 1 has much more of the proven cam protecting elements in it. This may be healthier for our high cam and slipper along with parts of the cam switchover mechanism.
Here is a TSB writeup about them...a how-to in case one snaps:
If I had to do this I'd yank both cams and reset the shims to perfection based on a hot engine clearance. It's much easier to just change out the bolts from time to time.
“What Causes the
When you hit 6200 RPMs, a solenoid valve (near the oil filler cap end of the head) opens. This sends high pressure oil down both rocker shafts. The high oil pressure overcomes the spring holding the Rocker Arm Pin in the low lift position. The pin is forced under the slipper follower which activates the high cam. While on the low cam, the high cam's Slipper Follower pulses up and down, following the high cam profile but producing no useful action.
There are 8 of these rockers to be switched over. Each rocker handles a pair of valves. The tip of the Rocker Pin and and bottom of the Slipper Follower experience switchover wear as previously noted and diagramed a few posts up... I'd guess they'd prefer EP oil additives...
“Improving the Lift Bolts”
Here are some closeups of the
Our lift bolts wear in the
place shown. When they break, the troublesome failures tend to occur in the
area of the nearby threads. I am unaware of any Lotus failures,
the Celica crowd has experienced failures over time.
The tweaked bolt benefitted from about 2 minutes of 1000 grit hand sanding: note the improved surface finish. This would favorably affect wear factors. A further tweak, not shown, is to polish the first few threads. The roots of the thread are the area to concentrate on - use a dremel to polish down there. This would double or triple fatigue failure life by reducing stress risers which lead to the PITA breaks in that area. As you can see the surface finish of the threads and wear area is not so hot. Of course this IS a 49 cent part with a reasonable lfe span, ha!
I think that a polished, latest design/build lift bolt would be a better tweak than cryo treatment if one wished to do so. Since friction and fatigue life factors are both inherently improved by the better surface finish. The latest silver bolts seem better than the gold colored bolts the engine came with. I'd have to research the oil flow through that area but it could turn out that a dab of cam assembly lube with EP additives could remain in place long enough locally to assist with lift bolt break-in.