Valve clearance adjustment issue
 

Hi Folks

Perhaps one of the shops or someone that’s built their own engine can give me a indication if this is a common issue:

I’m in the middle of reassembling my engine, I’ve had the heads ported and the valve seats cleaned, the shop I use has reseated all the valves and I’ve kept all the original shims in their rightful place, I was expecting to have to make some slight adjustments so I reassembled the heads on my bench to check clearances, and then again on the block to double check. Always using the correct torque specs and sequence.

There were a couple on the limit or just slightly out so I bought the required shims to bring them back into middle of the clearance spec.

Again I mocked them up on the block and they hadn’t adjusted quiet to the clearances I was targeting (I have used the OEM calculation to allow for rocker arm factor)

Round2: Bought some more shims and got all into spec, so I proceed to build up the engine, checking as I go all looks OK but I notice clearances have dropped a little, I just put the variance down to re-torquing the cam cradle etc. (Just to note all Cams are freely rotating throughout)

I set the timing etc and rotate the engine by hand through a couple of rotations to check everything, then I go back to the heads to recheck the clearances and there are quiet a few out of spec, some have dropped quiet a bit!

So at this stage I have dissembled and reassembled the heads multiple times and the clearances vary every time, Toyota love me as I’m their best customer for shims but it’s getting frustrating as it feels like a moving target.

Any suggestions welcomed, I’ll be buying more shims and trying again, I can only assume the new valves are bedding and maybe I should target upper end of clearance spec across the board.

Sorry for the long post

Word on the street from experienced techs is that the engine likes it more with the valves on the looser side. Here's a jumping-off point.


http://www.ft86club.com/forums/showthread.php?t=125672

Thanks for the reply, yes I had heard of those stories alright, perhaps these motors are just a real pain to get correct.

I’m targeting 0.14mm Intake and 0.24mm Exhaust clearance so just above midpoint of the spec, that’s if I can get the bloody things there consistently.

I would set them as loose as the book says they can be to allow for the valves to seat.

I've always struggled with valve lash no matter what engine. My day will come with this one. Curious to hear about how it works out. Good luck!

Just to be clear, are you checking the valve clearances with the cam carriers properly torqued down?

Yes fully torqued down on the heads, to OEM spec, then checked again once I have the full timing set and after a couple manual rotations of the engine.

Very strange. I haven't adjusted the valves on this motor myself yet. I have done tons of bucket/shim motorcycle engines and never had that kind of issue. I wonder if the base circle of the cam is slightly out of round?

I think the cams are OK, and even if they were slightly out of round I would imagine it still shouldn’t really vary each time I reassemble the engine, I’m being quiet careful about ensuring the cams are rotated lightly by hand (as per OEM manual) either side of base circle when checking the clearance just to ensure I’m getting a true reading. The rocker arm set up can make it difficult to know that your measuring at the right point on the cam.

I’ve also taken a micrometer to the original shims that I’m adjusting away from and although they do appear to have reduced/compressed in size by -0.01mm this still doesn’t account for the changes I’ve seen between adjustments and reassembly.

By comparison I can verify that the new shims from Toyota are pretty accurate, I’m seeing about +\-0.004mm on those.

Are the numbers all changing approximately the same way? Can you make out a pattern?

No pattern unfortunately, I’ve poured over every bit of data I have,

The only conclusion I’ve come to is that the valves have seated in differently having rotated the engine by hand, the clearance range is only 0.10-0.16mm on intake and 0.21-0.27mm on exhaust so I guess it’s conceivable that coupled with some slight variance in lifting and torquing the cam cradle each time it’s causing the change.

To be honest I’m not surprised there are issues with the new engines and Toyota recalls for springs too, I could easily have sealed up the engine if I hadn’t double checked after setting the timing and I would probably be throwing codes right now!

Or the seats weren't cut concentric

Oooo! Would reveal itself with some prussian blue, no?

I have not done valve lash on this car yet, but I agree with the loose adjustment since the clearances get tighter with wear.

I used to tend to lean toward the tighter side when I do valve lash.. for the extra lift lmao. Not practical for people who cannot refresh their engines every other month. I just end up having to service the engine sooner than later for imperceptible gains. But then again, how often do these engines need to have the valve lash checked anyway?

Each time you check the clearances after rotating the crank is different? Or, does it change from the initial setting then stay that way? Do the clearances become tighter or looser when this happens or is it different each time? Maybe the machine shop messed something up when they did the port job?