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post #101 of 119 (permalink) Old 03-08-2017, 10:34 AM
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Correct, there is a small spring keeping the slipper pad in contact with the cam but the spring is too soft to allow valve actuation. Once the rocker arm pin slides under the slipper pad there should be a measurable "lash" in the system. I am just wondering if this is part of the problem but I don't know how one would go about trying to measure it.
I believe, when you say lash, you mean preload on the slipper... As mentioned above the slipper was designed for contact when the big lobe is disengaged as well....


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post #102 of 119 (permalink) Old 03-08-2017, 11:33 AM
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If the big lobe always has a preload on it, then how can you possibly shim the big lobe it correctly? I mean obviously if you use too big of a shim on the big lobe side, at a certain point it's going to affect the small lobe. But once you get the small lobe dialed in, wouldn't the preload on the big cam take away your ability to check the lash on the lift side?
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post #103 of 119 (permalink) Old 03-08-2017, 01:24 PM
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I guess that is my point, there does not appear to be a way/procedure for checking the clearances of the cam lobe/slipper pad that proves to be problematic.
This is a good point. Once the slipper is locked in place, the locking pin, the shaft of the slipper, and their locations in the rocker have all changed the tolerance between the cam lobe, the rocker and valve stem. Essentially, the clearance that was measured when the locking pin is not engaged is most likely different from when it is engaged. However, there is no way to set clearances on the low cam separately from the high cam unless you can vary the thickness of the locking pin or length of the shaft on the slider, so it's really up to trusting that Toyota set the relationship between the roller follower and the locked slider correctly.
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post #104 of 119 (permalink) Old 03-08-2017, 02:06 PM
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Once the rocker arm pin slides under the slipper pad there should be a measurable "lash" in the system.
That isn't how I am reading the schematic. With the pin locked, there can't be lash since the cam can now exert force.

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post #105 of 119 (permalink) Old 03-08-2017, 03:06 PM
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That isn't how I am reading the schematic. With the pin locked, there can't be lash since the cam can now exert force.
There's a good bit of add'l plunge once the locking pin is engaged. Again, the lash doesn't seem to be the main driver. It may not be a factor much at all.

Unrealistic people will call for controlled studies, etc. I've probably built and studied this motor as much as nearly anyone on the planet and the answer to this issue is not perfect and won't likely be perfect.

Oil temp, possibly oil supply, possibly the marriage of the two metals, possibly the initial run it, and perhaps possibly ski jumping or the basic lobe profile are at play in general --or valve float... As I'm mentioned before, the race cars tend to have fewer issues than the street cars. TEND to. They spend more time on the big cam and run more appropriate oil temps.

So what all changes with race cars. They usually don't run front mount oil coolers, so they don't have pump issues of moving oil down 20 foot of hose or over cooling. Some have built motors with aftermarket cams. Some have built motors. Some have stiffer springs. They all have baffled oil pans, but I doubt there's much to that.

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post #106 of 119 (permalink) Old 03-08-2017, 03:51 PM
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I believe, when you say lash, you mean preload on the slipper... As mentioned above the slipper was designed for contact when the big lobe is disengaged as well....
No, by "lash" I am talking about the amount of added clearance in the system, from cam lobe to slipper pad, to rocker arm pin, to rocker arm, to valves.

But as you have stated in other posts, lash does not appear to be the culprit. I would just like to know what the lash is on the high speed lobe when it is engaged.
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post #107 of 119 (permalink) Old 03-08-2017, 06:52 PM
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I believe, when you say lash, you mean preload on the slipper... As mentioned above the slipper was designed for contact when the big lobe is disengaged as well....
No, by "lash" I am talking about the amount of added clearance in the system, from cam lobe to slipper pad, to rocker arm pin, to rocker arm, to valves.

But as you have stated in other posts, lash does not appear to be the culprit. I would just like to know what the lash is on the high speed lobe when it is engaged.

If there is preload on the slipper pad, won't the lash also be zero?
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post #108 of 119 (permalink) Old 03-09-2017, 05:19 AM
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Yes, "lash" between the slipper and the cam is always "Zero" - they are always in contact, slipper engaged or not, which is why you need to measure valve lash between the valve stem (shim) and rocker arm. You have to pull up on the rocker with some force, compressing the slipper spring, to get the roller rocker to contact the cam to measure valve lash.

Phil is right about this issue - it is obviously a design from the factory that is on the edge of reliability - depending on a variety of factors it can occur or not occur. Due to the number of variables, even using a Six Sigma DOE it would likely take 16 or more controlled experiments in a lab environment to make a conclusion, and the conclusion would likely be a combination of 3-4 or more factors that contribute to the failure.

Given that the the root causes and all of the factors will probably never be truly known, we do know there are things you can do to prevent it / reduce the chances of it happening:

- Run a wide lash on the intake side - .015 - .020
- Use liberal assembly lube and the "correct" amount of break in miles (amount is still up for debate)
- Make sure your oil is up to temp before getting on big cam
- Delete sandwich plate in street cars
- Laminova or other oil cooling system (BOE system listed above)
- Aftermarket cams seem to fare better than OEM
- Use good oil and change it frequently
- still no guarantee it won't happen again

Honestly, it should be a manufacturer warranty issue, or at the very least a TSB should be issued to address the problem. Porsche faced a class action law suit for the IMS issue that affected only around 5% of their cars. The only reason I can think that this hasn't gotten to this point is the problem is relatively cheap to fix versus the IMS issue which grenaded the motor in a Porsche. (10k+ to fix).

I'm done talking about it.
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post #109 of 119 (permalink) Old 03-09-2017, 10:19 AM
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Once the rocker arm pin slides under the slipper pad there should be a measurable "lash" in the system. I am just wondering if this is part of the problem but I don't know how one would go about trying to measure it.
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There's a good bit of add'l plunge once the locking pin is engaged.
Coincidentally I just checked this the other day while trying to diagnose an absolutely crazy high cam mechanical issue. I was able to lock all the rocker pins for the high cam with air pressure. There is a lot of travel in the pad when the pins are engaged. The pads appear to move as much as 0.10" when the pin is engaged, though this is only a guess I did not measure it. I can measure it next time I run this test.

The procedure is to remove the cams from the engine as well as the oil pressure sensor from the OCV housing, the one above the flywheel. Replace it with an air line fitting, it's a standard pipe thread. Reinstall the double cam cover (the one on the timing side of the cams) to cover the two oil ports. There is one more oil vent port to temporarily plug or cover with your finger, then you can apply 60 psi to the rockers. This locks all the pins in place and allows you to push down on the pads.

The issue with my engine was that two of the exhaust rocker pads would travel all the way down even when air pressure was applied.

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post #110 of 119 (permalink) Old 03-09-2017, 12:00 PM
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There is a large body of people who believe a proper break in, or marriage between the lobe and the follower is important. So maybe assuring we do that, and then carefully look over the lobes and look for defects before flogging the beast? What should the honeymoon look like, and how long should it last?
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post #111 of 119 (permalink) Old 03-09-2017, 12:16 PM
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There is a large body of people who believe a proper break in, or marriage between the lobe and the follower is important. So maybe assuring we do that, and then carefully look over the lobes and look for defects before flogging the beast? What should the honeymoon look like, and how long should it last?
That's been largely debunked; at least anecdotally plenty of failures have happened with cars that never were flogged at all.

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post #112 of 119 (permalink) Old 03-10-2017, 03:47 AM
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Rob Dietsch of Dietsch werks believes very strongly in the break in theory, they spec out a 1000 mile break in period after a cam change - and he lives/breathes lotus every day. Not saying it is or is not a major issue, just saying that there are some very knowledgeable people who believe it is a big factor.

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That's been largely debunked; at least anecdotally plenty of failures have happened with cars that never were flogged at all.
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post #113 of 119 (permalink) Old 03-11-2017, 09:24 AM Thread Starter
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100 miles in. So far so good.
The new oil thermostat I got did not improve oil temps. Going to move forward with my original plan of removing the sandwhich plate completely and see where that leaves me.
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post #114 of 119 (permalink) Old 03-11-2017, 10:10 AM
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My car is in transport back from BOE. They plugged the plate. I had one cooler covered, but instead of covering the 2nd, they said to plug it.

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post #115 of 119 (permalink) Old 03-22-2017, 09:05 PM
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Ok just to add my experience with this.

After pulling my valve cover to inspect the cams, all of them were pristine except for the third cylinder(second from the driver's side). It's not that bad but it's starting to build a ridge so it's only a matter of time. The car drives fine and no error codes. You won't even know a thing unless you pulled the cover.

However, I'm starting to think that valve lash might not be the major culprit in this. I measured the lash on all of the lobes and they were all on the limits of the high side according to Toyota specs. I did two sets of measurements using both the Celica and Matrix method. Below is what I got.

Celica method (measuring at the valve shim/rocker)
small lobe/big lobe: 0.010"/0.010", 0.010"/0.010", 0.010"/0.010", 0.009"/0.009"

Matrix method (measuring only the small cam where the lobe meets the rocker)
0.006", 0.006", 0.006", 005"

I was actually very surprised to find that the lash was already on the high end of both methods and that they were actually very consistent in lash across the board. Only the third cylinder cam lobe is starting to wear. I'm thinking that this is more of a oil temp issue so I'm going to run without the coolers after I replace the cam.

By the way, has anyone had any luck with swapping in the new rockers/cam and having the lash not change much? If I have to change the shims then so be it, but was just wondering what your experiences were and if I'll get lucky.
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post #116 of 119 (permalink) Old 08-28-2018, 05:13 PM
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OK had some hesitation and stumbling on acceleration on Sunday. Similar to this
Well I pulled valve cover and after 30K miles and 20+ track days the lobes are still good. Some signs of wear but nothing to be concerned with. All smooth! It turned out to be a cracked O ring on MAF. So simple. Anyway here are the pics of high cam cam lobes. So It may seem that some cars are more susceptible. All valve clearances were .01 and up. This is a VF1 MP62 running 7.5 lbs boost. Tommy
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post #117 of 119 (permalink) Old 08-28-2018, 05:22 PM
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Pics are not best but be assured there are no divots or irregular surfaces. 3rd cylinder looks weird but still flat and smooth. So still unsure what the consensus is on cam wear. I use redline 10W40 every year with 4 OZ redline break in additive. This car is tracked once a month. 3, 20 minute sessions. Tires seem to be my biggest wear item. Replacing valve cover gasket as it is 13 years old. Along with small O ring on cam cover lubricant tube. Tommy

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post #118 of 119 (permalink) Old 04-15-2019, 06:35 PM
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Just finished replacing my intake cam and rockers last weekend. I was at full throttle at about 7k RPM when the car went into limp mode with a p1302. #1 and #3 cam lobes were REALLY badly worn and #3 rocker was broken. Car has 35k miles, of which I've done about 3k.

This was a pretty painless fix. I went with the MWR cam in the hopes that it'll last a little longer. Everything aside from the rockers and camshaft looked pristine. The lift bolts, VVT screen, and rocker shafts were fine. I find it odd that the vast majority of failures are with the 1st and 3rd cylinders. Seems like it must be a balance/harmonic thing with this engine that causes this, no?
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post #119 of 119 (permalink) Old 04-16-2019, 07:55 PM
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What kind of rockers did you purchase?
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