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Discussion Starter #1
Head and block work are done, finally, so I lowered the head onto the stock gasket on the block and the front couldn't seat. The piston was all of the way up and the valves were fully extended, resting on the piston. I rotated the crank and extended the valves on all the other cylinders and #1 is the only one to have interference.

The top of the piston in cylinder #1 is marked like this:

< 1
3
the other five are like this:
< 2
2

I assume that #1 is an oversized piston but the valve relief cuts on it are ~3/16" from the edge, while the valve relief cuts are ~1/8" on the five other piston tops. The dish is the same on all of them and the piston raises to about the same height at the deck as the others.

When I got it, the JDM engine had three cylinders with bhg and the head gasket was deformed in other three. The gasket was of the "new" design, suggesting that a previous repair had been done- improperly. I think that the original #1 piston had been replaced with the one now in the engine but the head was not milled so the valves did not hit the replacement piston.

I had about four thousands removed from the head and also lapped the block. This apparently removed enough material to allow the #1 piston, but none of the other pistons, to contact the valves.

I do not think that this is a NA piston because the dish is like that of the others. The only difference is the spacing of the valve relief from the edge.

Is it OK to use the dremmel to cut the valve reliefs properly or does someone have the correct piston to replace this one?
tom
 

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Dr Wheelspin Rh.D.
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N/A piston


turbo piston


There are no 7m pistons that won't clear the valves, turbo or n/a doesn't matter, even oversize should clear the valves since you cannot change valve spacing. Cutting your own valve space is a bad idea, if the piston doesn't clear you need to replace it with the correct piston.
 

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agreed, dremeling will be bad. you dont want to change the weight of a balanced assembly.

Are your shims adjusted correctly for your valves? You may be pushing down too far.

Or, DID YOU MACHINE THE TIMING COVER WITH THE BLOCK? Maybe its holding it up.

What is the piston to deck clearance? A straightedge and a feeler gauge should tell you the answer to that with the piston at TDC. Hopefully, your JDM engine deck wasnt already machined beforehand.

Last but certainly not least, be sure to take accurate measurements of all required components and calculate compression. Find an online compression calculator that considers HG thickness and HG bore diameter, the standard engine measurement stuff, piston dish volume, cyl head volume, piston deck clearance. Dont get a sucky calculator with only a few, standard variables. You may have to correct your compression with an aftermarket MHG. I wouldnt put a stock gasket back on anyway.
 

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I've had four JDM and two USDM 7M-GTE's apart and all of them had the Pistons with "2" on them. HTH.
 

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Discussion Starter #7
Nice pictures, Bishop.

As things stand, I am disinclined to replace the #1 piston, though it is anomalous. I think that I will cut the valve reliefs to clear the valves.
Here is my reasoning: 1. After the piston in question was installed the engine was run long enough to seat the rings, and hard enough to blow the head gasket. This suggests that the piston was within spec except for the location of the valve reliefs.

2. Grinding the existing reliefs approximately 1/16 of an inch will not remove sufficient material to unbalance the mass at near-stock performance levels.

3. Because the stock removal will be only in the horizontal plane there is no danger of weakening the piston- this piston will then be identical to the other five.

4. The rings are already seated so a new set will not have to be seated.

Here is what can go wrong if I do as I intend: failure to cut sufficient valve relief may result in bent or broken valves and possibly a rebuild or replacement of the motor. Slightly out of balance piston could result in rapid wear of the bearings, shortening the useful life of the motor.
 

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Dr Wheelspin Rh.D.
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I wouldn't bet on 1/16" not affecting the motor. We're talking about a part that spins at thousands of RPM, just a little bit of inbalance is all it takes to mess up the equation. You will probably feel extra vibration or in the very least it will rattle the motor to pieces eventually.
 
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