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Thread: Recommended strategy on a bad valve

  1. #1
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    Recommended strategy on a bad valve

    I have a 93 Previa Alltrac LE and I love it. It has been dealer maintained until about 3 years ago when I decided the dealer route wasn't really buying me anything more than a good mechanic with a solid knowledge of Toyotas could.

    About two weeks ago, it started running a rough, most notably at idle and the mechanic I took it to, who had had it about a year ago for a repair, seemed to think it was a bad valve. He gave it the once over, tuned it, cleaned the injectors replaced the distributor cap and the wires but really didn't fix the issue. Again, he felt the problem was a bad valve. I hadn't even opened the engine access under the passenger seat, or done anything more than a brake job on this Previa, even though I'd say I am mechanically inclined and even worked as a mechanic for a couple of years in the mid-1970's but things are WAY different now and although I could easily service my 79 Hilux, I never even thought about any engine work on the Previa.

    Local estimates here in San Antonio are $3k-$6k for a motor replacement and my dilemma is that I love this vehicle and don't want to give it up but don't want to drop $6k to get it fixed. 285k miles. New tires. Completely new A/C system about 3 years ago. Replaced the rack and pinion 4 years ago. So, the vehicle is in good shape, until this valve problem. Pretty sure that it is a bad valve. There is a distinctive "chirp" on acceleration. I can pull the #2 spark wire with absolutely no effect on idle (still very rough). The "flap" test on exhaust has the paper being pulled back and forth and the engine idles. Diagnosis: Bad valve on #2.

    So, here is the question: I don't have a lift rack (wish I did). I have basic tools, socket wrenches, torque wrench, other basic stuff, so am I nuts to try to drop the engine out and either have the head rebuilt, buy a head or just find a good used engine, if that is possible, and go that route? I read multiple posts here about head gasket replacement and it looks fairly gnarly for a casual mechanic. I have a two week break coming up and I think I can drop the engine in a couple of days, if it doesn't take special tools or skill. I can methodically disassemble almost anything, my concern is getting the head re-installed correctly and not missing something essential when I reassemble.

    I hate to give up my Previa but I don't want to get 1/2 through this process and find that I am stuck. Sorry for the lengthy post. I just need a go or no go here. You don't know my skill level (not sure I do) but I am will to give it a go if you feel someone with intelligence, some experience and perhaps $2k to invest could do the job in his own garage. I have jack stands and a floor jack (how high should they go?) and time...

    Go, or no go?

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    Re: Recommended strategy on a bad valve

    Go!

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    Re: Recommended strategy on a bad valve

    I replaced the engine myself early this year. It was the first time I ever attempted changing an engine. It took me 3 months to replaced the bad engine with a jdm replacement. I only worked weekends however. It was a big challenge, no exaggeration. Why not just purchase a JDM engine, instead of trying to fix your tired, high miles engine? Mine turned out fine, and is running great. Whole thing was $795 delivered.

    https://forum.miata.net/vb/showthread.php?t=630410

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    Re: Recommended strategy on a bad valve

    Quote Originally Posted by Kurtanius21 View Post
    Whole thing was $795 delivered.
    So, some questions about this. I have flip-flopped on the "whole engine" idea a couple of times. I don't mind doing it, it probably isn't a whole lot more work than dropping the engine and pulling heads, etc... but my concern has been the quality. You don't know what might be lurking in a "used" engine...I'll do some more research.

    So, a couple of questions: How much stuff did you have to transfer from old engine to new? Was the engine an exact match? How high do you need to lift the vehicle to clear the engine? What tools did you end up buying/borrowing? Were there any tools beyond the "standard" set of rachets, sockets, screw drivers, etc that you needed (a "specialty" tool)

    I am willing to give this a go, I just don't want to come to a dead halt because I didn't have something that I needed to complete the job. The plan is to do this in my garage (residential) so just trying to prep for the project.....

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    Re: Recommended strategy on a bad valve

    Quote Originally Posted by Kurtanius21 View Post
    I replaced the engine myself early this year. It was the first time I ever attempted changing an engine. It took me 3 months to replaced the bad engine with a jdm replacement. I only worked weekends however. It was a big challenge, no exaggeration. Why not just purchase a JDM engine, instead of trying to fix your tired, high miles engine? Mine turned out fine, and is running great. Whole thing was $795 delivered.

    https://forum.miata.net/vb/showthread.php?t=630410

    NICE!

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    Re: Recommended strategy on a bad valve

    For the money's worth, I'd just get an engine replacement.

    I'll have to find my thread, but I rebuilt my engine from the ground up. Everything in the Engine is new. I spent a few thousand, but the motor and transmission run great and I have not issues. But I probably went the most expensive route.. and my outlook was that I am keeping the Previa forever, so I didn't shortcut or cheap out... Everything is Toyota OEM.. which was forced onto me because many of the guys on these forums are OEM purists.

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    Re: Recommended strategy on a bad valve

    So, I got the 1993 Previa manual on Ebay and that, plus the other videos I have seen, have helped me to feel a little more secure about the whole process. I have about 6 full days available to me and I hope that, plus a couple of weekends will allow me to get it all done. I still have unanswered questions that I could use some help with. I plan to start this whole shindig in a few days....

    My biggest concern isn't with disconnecting everything and even finding a replacement engine, it is getting the engine out, once everything is disconnected. From what I have seen, it looks like you need to raise the engine a bit in order to get the engine mounts off but what I can't quite tell is if it is a straight shot down from there. I have seen a couple of pictures that show the engine/tranny at an angle (front to back) and resting on a floor jack. I also saw one that had a hydraulic lift in the vehicle and then lowered it with straps. I looked through the lift options at Harbor Freight for ideas and it looks like a motorcycle lift might work or a transmission lift but I'd have to see where I could rent one. But, getting it down and then getting it back up is my biggest worry. How is this accomplished? And, is it a straight drop down once everything is disconnected and the motor mounts are removed?

    But going back to my other questions that went unanswered:

    How much stuff did you have to transfer from old engine to the replacement? Was the engine an exact match? How high do you need to lift the vehicle to clear the engine? What tools did you end up buying/borrowing? Were there any tools beyond the "standard" set of ratchets, sockets, screw drivers, etc that you needed (any "specialty" tools that were absolutely required)

    I'd love to get some answers on those questions.....

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    Re: Recommended strategy on a bad valve

    Special tools arenít really needed. Just a crane, engine stand, tie downs, and maybe a scissor jack to help stabilize the engine and transmission while you are lifiting it. Get some dowel rods and plywood sheet so you can roll the engine out from underneath the van. That way you only need about 20 inches clearance to roll the van engine out. Youíll have everything youíll need ultimately. You may want to get the Intake and exhaust gaskets. Typically the intake and exhaust need to be swapped on a Japanese engine.

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    Re: Recommended strategy on a bad valve

    I think the best advice you can follow is donít rush yourself. If you are rushing to get a project like this done, your odds of succeeding diminish. Like I said, it took me 3 months. Really consider if you have the time to do this. That being said, it only took me 2 weekends to drop the engine. A little tricky, but doable.

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    Re: Recommended strategy on a bad valve

    Peteh - as far as swapping "accessories" over to the "new" motor.
    You won't really know till they're both sitting side by each.
    JDM engines do come in more configurations than they do here so it is possible to get unicorn motors ..... but generally the basic long block is the same.
    The worst I have run into was needing to swap int/exh and oil pan/pick-up tube, but generally its all pretty straight forward.

    I tend to prefer going with the original accessories, unless there is strong reason not to.
    Had a Celica once that I did a JDM replacement, it came in with a twin carb set-up, obviously, I did not delete that.

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    Re: Recommended strategy on a bad valve

    So the "rest of the story" is this:

    After spending quite a bit of time watching videos, reading posts, and identifying all that I would need to do the job, I decided NOT to replace the engine and instead donated the Previa to Habitat for Humanity. If I had had the time, the tools and a garage that could handle having all that stuff laying around for a month or so and could face the frustrations with finding parts and reassembling everything correctly, I would have done it. But, I weighed all the "costs" versus the return and decided it was time to retire the old girl. If I could have found a competent garage here in San Antonio that could do the work at a reasonable cost, I would have. But I got no takers.

    I love my Previa! Best vehicle ever! But it was time to let her go and she's gone.... :-(

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