7MGE compression too high...now what?

[rbutton]

86.5 NA. Second HG replacement in only 138,000 miles. Bought a refurbed head from Clearwater Cylinder Heads, a 1.2mm HKS MHG, and 85ft-lbs ARP bolts - hoping to be the last HG that I have to replace.

Once everything was back together I measured the cylinder compression. They ranged from 155 on #1 to 180 on #5. Most were 175psi. Whoops!!

Once back together and the plug wires installed properly idle was a little rough around 10 degrees BTDC. Increased to about 18 degrees and the idle was smoother, but on the road the engine lacked power. Also seems to be some exhaust detonation, especially when getting off of throttle. Still running on the full tank of 87 octane gas that I put in 7 months ago.

Thinking I need to have the 25 year old injectors cleaned, leak checked, and balanced. Any other thoughts?

 

[AJ'S 88NA]

Run 91 with the higher compression it will help. My compression i was around 190 last time I checked it, 175 -180 isn't bad, but why the difference?

Did you use a timing light and jumper wire?

 

[rbutton]

Run 91 with the higher compression it will help.
Did you use a timing light and jumper wire?

Once I get some fresh 91 octane gas in the car, is there anything I need to do to speed up ECU re-learning?

Yes, of course timing light and jumper wire when the car was warmed up.

I do need to double-check that the harmonic balancer is still aligned with TDC. Apparently ran with it loose for years and the crank key slot is a little munged-up, so the balancer is able to rotate a few degrees if the bolt isn't tightened down enough.

 

[AJ'S 88NA]

Won't affect the ECU.

Why the difference in compression if everything was new?

 

[rbutton]

Why the difference in compression if everything was new?

Didn't do anything to the bottom-end, so I suppose the rings could be affecting the compression differences between cylinders. Also, I may not have cranked the engine as long on cylinder 1. I wasn't watching the gauge on that one while cranking - so that could be the odd man out. All others were 170-180 psi.

 

[hvyman]

Also could be the timing cover if it was flush with the block. A mhg really needs the black and timing cover machined to be done properly.

Id also back the timing down to 10. 12 max.

 

[rbutton]

Went back to check timing alignment and looked to be one tooth off (cam marks too far left). So I just adjusted that.

I mentioned earlier that my crank key is munged up from probably running loose for years. There's a BIG gap on the left that allows the harmonic balancer to slip counter-clockwise several degrees. I'm going to try to "fill-in" the gap with something like JB Weld to see if that helps keep things aligned.

Anyone seen something like this? Any other thoughts?

 

[AJ'S 88NA]

Buggered up key way happens a lot actually.

 

[hvyman]

Might want to fix that. Either buy having it welded in or replacing the crank. If that balancer comes off motor is going to be toast.

Also if you were putting the engine to tdc based of the crank pulley better pull no1 plug and make sure its on tdc.

 

[rbutton]

Update.

Had time this weekend to get the crank and cams aligned by taking off the harmonic balancer and aligning the key way perfectly vertical. Dropping stick in #1 spark hole is too subjective. Everyone knows the derivative of a sine wave at 90 degrees is zero - this means near TDC the stick is barely moving vertically even as the crank position changes by +/- 5 degrees. I was off by one tooth, so I fixed that.

Re-checked the cylinder compression - this time cranking 8 times for each cylinder. Here's my new results -
1-190, 2-187, 3-192, 4-193, 5-194, 6-194. MUCH BETTER! Gauge doesn't go to 0psi when all pressure released. Starts at about 9-10psi.
Added bottle of octane booster to my full tank of 87 gas.

Used JB Weld to "fill in" the gap in the crank key way. Put a little extra on and carefully slid the H.B. onto the crank and let it set over night. Installed H.B. bolt the next day and really cranked it down using a ginned-up SST. My H.B. had two holes on the surface, so I used a 6" by 36" piece of 5/8" plywood, hole saw near the end for the 19mm socket and two smaller holes for screws aligned in the right place. I was able to really torque that bolt down better than I ever had.

Re-assembled everything and started the car up. Was running rough and there was no mark when I went to adjust timing. Found #1 and #2 wires were swapped. Duh! Keep forgetting that #1 wire is longer than #2. Got that straightened out easily enough and started the car.

Ahhh! My smooth N/A Supra is finally BACK!

Set timing to about 10-11 BTDC and drove it around. The car pulls way more than it has in years! Power is really good starting around 3000-4000rpm.

Thanks for all the advice.

 

[hvyman]

Ugh. Sticking te stick in no1 and watching it hit the top most part is by far the most accurate way other than putting a dial caliper on it.

Also the crank pulley bolt is supposed to be torqued to 198 ft lbs.

 

[AJ'S 88NA]

Glad you got her running. Probably have to eventually address the crank pulley, definitely keep an eyeball on it.

 

[BlackDynamite]

I had the same problem with my 87....My key way was damaged, so i centered and got this industrial locktyte. Worked fine for me. The head and block were milled down at a minimum of 10 thousandths on both head and block. i used a stock head gasket, ran 93 octane, 14-15 Degree timing, no cat, and a 2.5 exhaust. I had a slight backfire after the first few shifts, after a cold start up during winter...it ran great the whole time i had it. It would barely run on 87 and would get a little detonation until it warmed up.....at the same time, this was a 700$ car and i beat this shit out of it everyday for 2 years...never letting up on it....one of my favorite supra's I've had....though i wish it had a LSD....LOL

PS: It was an automatic before i switched it to manual. It ran off a automatic ECU, and was basically in park all the time.....Which caused it to run richer....even while driving....Cold, damp nights were sweet at high RPM...

 

[rbutton]

Ugh. Sticking te stick in no1 and watching it hit the top most part is by far the most accurate way other than putting a dial caliper on it.

Also the crank pulley bolt is supposed to be torqued to 198 ft lbs.

I found I could turn the crank back and forth about 10 degrees and not detect any vertical movement in the stick. Too little movement of the pistons at the top. I found aligning the crank keyway to work best. I suppose the stick will do in a pinch if you didn't want to pull the harmonic balancer.

198 ft. lbs !!! Holy crap, I'm going to need a longer pipe!!

 

[hvyman]

Thats because there is no oil pressure. You wouldnt get that with the engine running.

Torque wrench would work better as well.