Hi, another question about my 7MGE straight 6 engine. The valves are adjusted with shims. I am familiar with this system since my Fiats had the same thing. About 10 years ago I had measured the clearances, and now they seem to have tightened about .001". Is that normal? I guess the valve seats are wearing a bit? Anyway, here is my main question: If the allowable range is say .025"-.030" (I am going from memory here), would it be better to be at the smaller end of the range or the larger? Also, how significant would it be to be .001" over or under the limit?

Thanks,

Mike

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

Hi,

I hate to be a thread bumper but I really need an answer to this question. I suppose I could just post a valve adjustment question over in tech. But it is a Toyota so I put it here. Any info would be appreciated.

Thanks,

Mike

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

I would rather keep them on the looser end of the spec than tighter end, the straight six is Yamaha designed and follows the same pattern of shim under buckets like the Yamaha 750 engine I had on my FZR-750.

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99 Gurkha with OM616 IDI turbo

2015 Gurkha with OM616 DI turbo

2014 Rexton W with OM612 VGT

I have been told that the shims are interchangable with the Yamaha 750 shims. But they are both too expensive!

Thanks,

Mike

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

Just curious - on an engine with shim-adjusted valves, do you have to loosen/remove the camshaft to insert/remove the shims?

No. They make a tool to depress the "puck" (tappet/or shim holder). Basically it just presses the valve in a bit. I suppose you have to make sure the piston is not TDC. Then you fish out the shim with a little screwdriver, or some people use compressed air to lift it up a bit. The Toyota tool looks sort of like funny pliers. The Fiat tool is hard to describe. Basically you turn the engine until the cam lobe is pressing in the lifter, then you insert the tool which has like a finger on each side of the cam lobe, and then you turn the cam so the lobe is away from the lifter but the tool still presses against it keeping it down, opening up a space to remove the shim. I suppose it is faster to do it than to explain it!

My exhaust are supposed to be .020" to .030" and a couple are at .031". Some that were at .031" before are now at .030". One is at .025". I am not sure if I really need to change anything.

I am guessing tight exhaust valves will lead to burned valves and tight intake will rob power?

Mike

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

The valve clearances I have seen for that engine are much smaller, somewhere around .010" and .012".
.020"/.030" seems not only way to much but too wide a tolerance. Valve clearances are typically +/- .001"

On a shim-under-bucket engine you do indeed have to remove the camshaft to change the shims. This is because the bucket must be completely removed to access the shim - it's _under_ the bucket. I rather doubt there are any automotive engines left using this design. I do know the "classic" Jaguar straight six used shim under bucket, hence labor for a valve adjustment was very high. This design is still common on high performance motorcycles. I owned a recent Kawasaki which used shim-under-bucket, and it was mucho work to adjust the valves and resync the cams. Accurate valve timing is rather important on an engine with a 14K redline.

I also owned a Ford sedan powered by a Yamaha designed and built DOHC 24 valve V6. It used the shim-over-bucket design as described earlier in this thread. The shim could be changed by using a special set of tools to slightly compress and hold the bucket. The camshaft did not need to be removed. But the valves never needed adjustment in the ~100K miles I kept that car.

- JimY

Some of the newer Mazda and Ford engines use bucket tappets of different size to adjust clearances.
The shim under tappet was used by Alfa and Maseratti in the Biturbo V-6.

Yes, the Toyota 7MGE is "shim over bucket". The clearance spec per the shop manual is exhaust .20mm-.30mm, intake .15mm-.25mm. This is measured cold of course.

Mike

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

I wouldn't worry too much about .001" too loose on an exhaust valve. Too tight I might, but not too loose. Everything swells and gets tighter when hot, and indeed too tight will cause burnt valves. Too loose will cause noise, but no harm.

Bear in mind, I'm talking about use as a daily driver, if you're planning something special for this engine I might try harder for the middle of the range.

MV

Well I double checked my specs and indeed I had them wrong, so I went back and edited my last post to show the correct specs: .20mm-.30mm exhaust, .15mm-.25mm intake !!

So that is about .008"-.012" and .006"-.010" I think.

Mike

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

That's much better. But you might want to get a second opinion if those figures came from a Haynes manual.