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Thread: Replacing a Previa head gasket.

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    Administrator timsrv's Avatar
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    Re: Replacing a Previa head gasket.

    If you lost the position of the sprocket on the chain I'd probably just pull the timing cover and set it up from scratch. Better yet, since you're in that far why no put a new timing set on. When I did my head gasket the timing chain started making a bunch of racket shortly after. I ended up going back in and doing a timing set. Tim

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    Re: Replacing a Previa head gasket.

    Thanks Tim , looks like it lost enough coolant to get overheated..... the valves are shot and head warped, with 260,000 miles I'm looking at a japanese replacement for 700,00. Wish you could put the diesel version in it ! 45 mpg sounds pretty good !!
    DOnny






    Quote Originally Posted by timsrv View Post
    If you lost the position of the sprocket on the chain I'd probably just pull the timing cover and set it up from scratch. Better yet, since you're in that far why no put a new timing set on. When I did my head gasket the timing chain started making a bunch of racket shortly after. I ended up going back in and doing a timing set. Tim

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    Re: Replacing a Previa head gasket.

    The Looking for a timing chain kit and I am glad I came across this.

    I clicked on that ebay link and the seller has some kits available.

    I was looking at those Evergreen kits on amazon, but I was unsure about them.

    I am glad to see that the timing chain guides are metal backed. The 1st year nissan 240sx had plastic timing chain guides and the timing chain would eat through that, then the timing chain cover, and where that was being cut was next to the water pump.

    I am wondering if that kit is good for the S/C motors? Or there is no difference?

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    Question Re: Replacing a Previa head gasket.

    Hi guys, I noticed on the photos of the blown HG engine, that the coolant holes in the gasket, even comparing to the new gasket are all very small except around the back of the #4 pot. How come the casting holes are so much bigger than the holes in the gaskets? Is this anything to do with the country/climate the vehicle is sold? i am down under in New Zealand. Do the restricted gasket holes contribute to overheating or head cracking? Just asking, if anyone has any comments, I would love to hear them. Thanks.

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    Re: Replacing a Previa head gasket.

    Update on motor from Japan,
    After two years and now at 325,000 miles still runs like new.... I'll check my numbers but also seem to be getting better mileage then new

    Quote Originally Posted by beoutside View Post
    Thanks Tim , looks like it lost enough coolant to get overheated..... the valves are shot and head warped, with 260,000 miles I'm looking at a japanese replacement for 700,00. Wish you could put the diesel version in it ! 45 mpg sounds pretty good !!
    DOnny

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    Re: Replacing a Previa head gasket.

    The first thing I would check, which you may have already, is your radiator... with a digital thermometer to see if it has dead spots....
    in my experience rigs with over 100,000 usually have radiator issues leading to over heating unless flushed regularly.... I know everyone says replace thermostat since it's cheap but it's critical to know the radiator is working as well.... Sorry if this is not related to you question.


    Quote Originally Posted by Garth View Post
    Hi guys, I noticed on the photos of the blown HG engine, that the coolant holes in the gasket, even comparing to the new gasket are all very small except around the back of the #4 pot. How come the casting holes are so much bigger than the holes in the gaskets? Is this anything to do with the country/climate the vehicle is sold? i am down under in New Zealand. Do the restricted gasket holes contribute to overheating or head cracking? Just asking, if anyone has any comments, I would love to hear them. Thanks.

  7. #27
    Administrator timsrv's Avatar
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    Re: Replacing a Previa head gasket.

    Quote Originally Posted by Garth View Post
    Hi guys, I noticed on the photos of the blown HG engine, that the coolant holes in the gasket, even comparing to the new gasket are all very small except around the back of the #4 pot. How come the casting holes are so much bigger than the holes in the gaskets? Is this anything to do with the country/climate the vehicle is sold? i am down under in New Zealand. Do the restricted gasket holes contribute to overheating or head cracking? Just asking, if anyone has any comments, I would love to hear them. Thanks.
    Restriction is an important thing when it comes to controlling flow. When they cast the block & head the main goal (regarding ports) is simply to insure they're there. The gasket is what's used to dial-in/control flow. Toyota spends a lot of money in research to insure they get it just right & sometimes product improvements continue for years. Messing with it by enlarging gasket holes would likely lead to other problems (you might be increasing flow to some parts at the expense of reducing flow to others). For best results be sure to use an unaltered OE Toyota gasket and you'll be golden. Check your head carefully for warpage and cracks before reassembly. I'd also recommend removal of the valves to check/inspect valve guides & valve seat condition. With the Previa, reshimming the valves on assembly is highly recommended and you should consider replacing the timing chains/guides. Good luck. Tim

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    Re: Replacing a Previa head gasket.

    Hey Tim.......Sorry about the incorrect posting, I thought I was posting to this thread. I hope I have it right now Glad to see you're still in the Prev business. I finally recovered from all my skiing and eye injuries and am back to putting my '92 Prev back together. I decided to rebuild the engine after an ignorant partial tear down to get the cracked head off. I read all the blog posts in this engine head forum but didn't quite come across an answer to my dilemma.

    When I took the original factory head bolts off (owned since new) I threw them aside, almost lost, only to discover them maybe in the nick of time. I found them to have a washer with them and when I went to install the new head with new bolts (ordered for a Previa head) I was following the official Toy manual to the 'T' saying nothing about installing a washer It only said to wet torque them which I did. All ten are identical to the old and torqued just fine and they didn't come with washers either. Everything else I've come across says nothing about washers. I noticed in one of your replies to this thread you talked about wet torque, etc, but didn't mention the washers. What in your experience is maybe the answer or your opinion. You've rebuilt these engines? Have any broke or went bad after some time and/or miles WITHOUT head bolt washers? I've gotten conflicting opinions on this. Like if they needed washers they'd be perm attached or come in the package with the bolts. Does the extra few millimeters of torque spread out with the washers on the aluminum head matter? I haven't run the engine yet, it's still out and nearing completion.

    Would really appreciate any guidance or info.....thanx much!

    John

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    Re: Replacing a Previa head gasket.

    Does it matter? Good question. Maybe? Too many variables to know for sure, but personally I wouldn't want to take the chance. Not having a washer would put the threaded tips of the bolts into new territory. Probably not much more restriction here (if any), but if there's any interference here it could affect final torque. Then there's the slipping action of the bolt heads against the hardened surface of the washers. Surface tension between those and the softer aluminum could also affect torque. Probably not by much, but it does add a variable. Personally I would remove each bolt one at a time, add washer, then reinstall/retorque. If you do each one while the others remain torqued, you wouldn't need to worry too much about messing up the head gasket and/or repeating the sequence (although I'd repeat the sequence giving each bolt the final 90 after all the washers were put back on). But that's just me, do what you feel is right. Tim

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