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1989 7MGTE Ice Blue Pearl,
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Discussion Starter #1
Back in Jan I bought an 89 Turbo parts car for $1,500 for the R154 and diff. Engine was not running at the time. After a few weeks of messing around found the TPS was not right and was the reason it would not run. Car ran good and strong after that. Long story short my plan was to take this engine and do a rebuild and put in into my 89 NA. During the tear down process we discovered that cylinder 5 and 6 had some damage on the top of the pistons and to the head. The worse seems to be the head for Cyl 5. I have pictures attached that are not the greatest since everything is not cleaned. What do you guys think my next course of action should be. Am I looking at needing another head? Pistons I know are going to need replaced. First picture order cyl5,cyl6, head 5, head 5 and 6 Thanks,
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I would save that by first cleaning ALL the carbon from it, then taking a small flat punch, and peening the high points of dimples back flush.
Maybe a light lapping, or even having .010" cut by a machine shop.
Don't forget to take any sharp edges off the squish area.

A performance mod would be to take most of that squish area out, which actually shrouds the valves, restricting flow.
You don't see any of that in a JZ, or RB engine.
Especially if going to larger valves.

One of the many Group-A heads that I had brought in from Japan
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My head
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I don't see the piston damage on 5, though I see a few pings on 6. That surface can be repaired on the piston and the head. Looks like a spark plug electrode got loose? On removing the material from the head, I'd be concerned about two things. 1 - you are dramatically lowering the compression by removing that material. 2 - The A head seems to be a race motor tuned for power very high in its RPM band. That could make it a dog in every day driving unless you're flogging it. The usual reason for those shapes in a production engine like the 7M is to promote cylinder swirl for good lower end torque and fuel mixing. Grind it out and you may end up with a peaky motor that's no fun as a daily driver. So unless someone has done this and dyno'd it to see what the impact on the power curves (torque/HP) is, I would counsel against. Now if you're doing a full performance rebuild with pistons that will make up for the lost compression, some professional porting and polishing - different matter. What I'm seeing is a build on a budget asking about re-using stock stuff here. Hope that's helpful to the discussion.
 

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1989 7MGTE Ice Blue Pearl,
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Discussion Starter #4
Thanks for both of your input. The plan was going to be machine head and block and re ring and new bearings. but now after this I'm looking at forged bottom end. Main concern for me was ( and I know until I take it to a machine shop ) if the head would still be usable. I could always use the head off my NA but really dont want to do that. Not sure if it was from a plug or not. The plugs I took out looked fine but I would agree that's what it looks like.
 

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Wait, what? You have an engine that ran fine, so you decided to tear it down and refresh it with a conventional rebuilt and a machine shop machining the heads and block then new bearings. Great plan. You found some damage from a prior incident that two of us said is no problem - proceed with your plan. Now you're saying "after this I need a forged bottom end"? So you want a forged crank and forged pistons? I think you are WAAAAAY overthinking this. Stick with your plan or quadruple your budget needlessly, I say.
 

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So, just curious about what you are thinking, CRS? I have a 7M block in the stand right now and wanted to see your plan and progress as well. Updates?
 

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1989 7MGTE Ice Blue Pearl,
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Discussion Starter #9
Well right now I took the block and head to a local machine shop.... Kinda had questions for you guys about that. Unfortunately I do not have any shops that I can find within 2 to 3 hours of where I live that knows much on imports. (All Domestic Focused shops). I have read sixpack say somewhere in a post before to not let a shop do what they do to chevys to a 7m because it will not be good enough. I have found a guy that is a big Mitsubishi Starion (inline 4) guy. When talking to him I told him I am going Metal / MLS head gasket. He made the comment well I will not be able to get mirror finish but thought he said it would be good enough for a MLS. I am worried it will not be good enough for what I am looking to do. My whole point in getting head and block decked is for the better head gasket / having to bore over STD. Going to call him in the morning and see if he has the device to read RA rating. What do you guys think I should do at this point? Kinda thinking I may need to pick it back up. but like I said I do not have any options...
 

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I think a good shop is a good shop and you're not having much highly demanding stuff done - though the boring to oversized pistons I must have missed, or that's a new part of your plan. On the finish, any competent shop should be able to achieve a metal finish so I'd be leery if he said something like that to me on ANY engine.
 

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1989 7MGTE Ice Blue Pearl,
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Discussion Starter #11
So talked to the machine shop today. Says the head front and back are .011 off from the center. Does this mean I need a new head? Can not find anywhere that lists how much can be taken off the head before its a paper weight. Does anyone have a list of tolerances that I seem to be unable to find? As far as I know the head has never been machined before. If at this point if I do need a new head does anyone know a good place to get one? Really dont want to take the head off my good running GE.
 

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I believe my machine shop told me .010. they cut like .012. should be fine.
You should be fine if the head hasn't already been cut before.
 
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