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So, the 5MGE in my 86 is pushing 240k miles. It's still running fine and isn't anything wrong with it...yet.

I'd assume with this kind of mileage the engine will soon start having problems. I want to get it rebuilt before anything major goes wrong.

Would it be a bad idea if I just get the head rebuilt? New valves, springs 3 way valve job, new everything and completely cleaned for 650.

Is that a fair price for that type of work?
Would only having the head done cause problems with the bottom end?

Would you guys recommend just pulling the whole motor and having the block done also? Not even sure how much that would cost.

  1. Any input would be appreciated.
 

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It will be big bucks to the the entire rebuild. NO,don't do just the head work-the extra compression will kill the bottom end.
Been there,done that.
It's probably an oil burner/leaker by now.
The down time to wait for your NEW engine will be hell.
I've seen FREE engines. I gave one away a few years back. That may be a better option for you.
The old one had 211,000 miles and it was really TIRED. Also a suspected BHG.
Figure about 2-3 K for a rebuild with your CORE.Give the re builder at least 4 weeks,minus parts delivery issues.
 

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For small airplanes, there's rules that you MUST rebuild your engine typically every 1,000 to 2,000 hours depending on the model and it has to be done by a certified professional. Of course you can't just safely coast off the side of the road when your airplane engine quits, but its all about statistical probability of failure increasing as running time increases. At 240,000 miles, if your Supra were an airplane, it'd have already been rebuilt about ten times by now.

I'm usually in the camp of "if it isn't broke, there's enough risk of error in repairing it that you shouldn't fix it", particularly when its amateur DIY. But in this case I agree with Dave, that the risk associated with the high mileage outweighs the risk of user error. Consider if something finally disintegrates in the block at 270K, you're going to do the head over again to clean shavings out of it. Therefore if you're going to do any of it, go ahead and do all of it.

I haven't priced a 6 cylinder rebuild in 20 years, but there's really no standard anyway. It depends what the machine shop finds is out of tolerance and they can give you a lot of options like porting and polishing, lubricity coatings, etc. Don't forget to take the timing chain covers with you to the machine shop as if they deck the block, they need to shave that too.
 
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