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Thread: Replacing a Previa head gasket.

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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.

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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 90º after all the washers were put back on). But that's just me, do what you feel is right. Tim

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    Re: Replacing a Previa head gasket.

    Thanx Tim for your kind input! I especially liked your thought about the head bolt slippage against the hardened steel washer. I also since your comment found in the Toy manual where it actually shows the washer in the illustrated breakdown of the head assy, etc, so I decided to install the washers. It took longer than I figured but like you said, better to be safe than sorry.

    Also, if you don't mind....WHAT if any, is the reason for the block insulator between the block and the intake manifold? I'm guessing maybe for sound and/or heat transfer from the engine but not required for a specific engine function? Mine got destroyed some years ago but now that I'm rebuilding this thing I thought I'd better make sure. Do you know or have thoughts about this thing?

    Thanx allot, John

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    Re: Replacing a Previa head gasket.

    Actually I'm not really sure what you're talking about..........is it Toyota part #12581-76010? If so, you can get these for around $85 at the on-line Toyota parts sites. Tim

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    Re: Replacing a Previa head gasket.

    I have a 1994 Previa LE, in excellent condition, however, it apparently needs a head gasket. I say that because since it was diagnosed by a shop I never went to before almost a year ago, it still runs really great. I recently had the oil changed and that shop said there was a oil fiter housing leak. I have no technical knowledge about this, have owned this car since new. Recently had to keep putting in new coolant, but now is ok. Upon first startup, there is white smoke out the tail pipe - is this due to the leak or ??

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    Re: Replacing a Previa head gasket.

    Quote Originally Posted by previa94 View Post
    I have a 1994 Previa LE, in excellent condition, however, it apparently needs a head gasket. I say that because since it was diagnosed by a shop I never went to before almost a year ago, it still runs really great. I recently had the oil changed and that shop said there was a oil fiter housing leak. I have no technical knowledge about this, have owned this car since new. Recently had to keep putting in new coolant, but now is ok. Upon first startup, there is white smoke out the tail pipe - is this due to the leak or ??

    Hello 1994 Previa,

    If you've been adding coolant and your Previa blows white smoke at all, it's burning coolant in the combustion chamber. This is due to probably one of two reasons or both especially if you have over about 200K miles on it....you either have a cracked head gasket or a cracked aluminum head. I had the same problem with my 92 Previa which was a cracked head and it will only get worse until you can smell the sweet odor of coolant. You have basically two options.....one is of course, replace the gasket and or head or pour some head and gasket sealer into the cooling system after it comes up to operating temp. Others have had varying success with this option and depending upon which product you select (there are about a dozen different ones) There are several U-tube videos on the subject dealing with the Previa engine. Some of them can clog up your cooling system.....I personally wouldn't try this unless I was desperate.

    If it's a cracked head, in some cases it can be repaired if the crack isn't in the wrong place. The head can in fact be removed without removing the engine thru the maint panel under the front passenger seat. See Youtube still pix video access code CMH 1129 and get a maint manual preferably an official Toyota if you're going to try it yourself. Hope this helps.....

    John in the Rockies

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    Talking Re: Replacing a Previa head gasket.

    Quote Originally Posted by John A Feider View Post
    Hello 1994 Previa,

    If you've been adding coolant and your Previa blows white smoke at all, it's burning coolant in the combustion chamber. This is due to probably one of two reasons or both especially if you have over about 200K miles on it....you either have a cracked head gasket or a cracked aluminum head. I had the same problem with my 92 Previa which was a cracked head and it will only get worse until you can smell the sweet odor of coolant. You have basically two options.....one is of course, replace the gasket and or head or pour some head and gasket sealer into the cooling system after it comes up to operating temp. Others have had varying success with this option and depending upon which product you select (there are about a dozen different ones) There are several U-tube videos on the subject dealing with the Previa engine. Some of them can clog up your cooling system.....I personally wouldn't try this unless I was desperate.

    If it's a cracked head, in some cases it can be repaired if the crack isn't in the wrong place. The head can in fact be removed without removing the engine thru the maint panel under the front passenger seat. See Youtube still pix video access code CMH 1129 and get a maint manual preferably an official Toyota if you're going to try it yourself. Hope this helps.....

    John in the Rockies

    Thank you for the input, John. I did read elsewhere that it could not be the head gasket if I have been able to drive the car for over the past year. Perhaps there is some spiritual intervention going on ??

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    Re: Replacing a Previa head gasket.

    I started working on replacing my head gasket today using the leave the engine in the van technique. Here are some pictures of today's progress.

    I got all but one of the exhaust manifold studs out. will work on the last one next time or take the head off with the manifold attached.
    20190825_113909rot.jpg

    I turned the engine to TDC and pulled out the distributor.
    20190825_113813.jpg
    20190825_113837_HDR.jpg

    I decided to remove the oil filter mount so that I would have a couple of extra inches to lower the engine when I take out the engine mounts. I am going to replace the rubber gasket since I have it off.
    20190825_113130rot.jpg
    20190825_113137_HDRrot.jpg
    Last edited by tfreed1; 08-26-2019 at 09:46 PM.

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    Re: Replacing a Previa head gasket.

    I removed the exhaust manifold using hammer, chisel, and heat to get the last stud out.
    exhaust off.jpg

    20190830_190112(1).jpg

    Removing the oil filter mount was useful as it allowed me to lower the engine quite a bit. I did not need to leave wood spacers after removing the engine mounts.
    lowered engine.jpg

    engine mount.jpg

    Next time. I'll take off the head and see the extent of the damage.

    Took out the cam shafts.
    cam out.jpg

    cam stuff.jpg

    Took head off.
    head out.jpg

    The gasket had blown. The fire ring for the number one cylinder is bent and water passage leaked to the cylinder.
    gasket.jpg

    There is some pitting in the block deck where the coolant leak occurred. I am not sure if this is something that the new gasket will fill or if there is some sealer that I should use in this spot with the new gasket. Any suggestions on this would be welcome.
    pitting.jpg

    pitting2.jpg
    Last edited by tfreed1; 09-02-2019 at 11:58 AM.

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    Re: Replacing a Previa head gasket.

    Any suggestions about how to handle the engine block pitting?

    pitting2.jpg

    The new head gasket uses a metal frame around the water passages. Hopefully, this is a design improvement.
    20190902_133858.jpg
    Last edited by tfreed1; 09-02-2019 at 12:47 PM.

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    Re: Replacing a Previa head gasket.

    I guess it depends on how deep the pits are. Machining (decking) the block is always best, but that would require complete disassembly and then hauling the bare block into a machine shop. There is a product made for this: https://www.amazon.com/Permatex-8069...20038934&psc=1, but in my years as a mechanic I've never used it. I usually consider things in cans to be gimmicks and some even cause more harm than good, but there are exceptions........not sure if this one of them.

    If the link above doesn't work, the product is Permatex Copper Spray-A-Gasket. It's available most places where auto parts & supplies are sold. Tim

    PS: For quality you can trust I highly recommend OEM Toyota for your head gasket. Other brands may be good or possibly even better???, but I'd consider other brands a roll of the dice. Good luck with whatever you do/choose.

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    Re: Replacing a Previa head gasket.

    Thanks for the information timsrv. I don't really want to coat the whole head gasket just to address the small pitted area. I may use a small amount of the Permatex or something similar just in the pitted area under the gasket. I would like to let the gasket seal its self to the block rather than using some other substance to do the sealing.

    I cleaned up the head and it looks to be in good condition with no warping when checked with a feeler gauge. The engine has never been over heated until the head gasket went at 244,000 miles. And it did not run more than 3 minutes at that point.

    20190902_202214 (1).jpg

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    Re: Replacing a Previa head gasket.

    I agree. If I ever needed to use that stuff, I think I would spray it in the pitted area, let it dry, then sand or file it smooth (assuming that can even be done???). When I've had similar issues in the past I've either chanced it or I've had the block decked. Tim

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