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Thread: 87 mmax G63b timing question

  1. #1

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    87 mmax G63b timing question

    I had the timing belt snap while getting on the highway in my 87 mmax G63b, initially i was told this was an interference engine and that i was basically screwed. After long searching, blogging, and talking to some mmax folks i found out that it is not an interference engine. I am trying to replace the timing belt myself, it is also worth mentioning that i am a Network Administrator and not a mechanic what so ever.

    My question is, which cylinder is my #1 piston in?

    I know that if i take the spark plug out, throw a straw or screwdriver in there and hand turn the crankshaft until that cylinder is tdc, i can work from there. I tried this on the cylinder closest to the front of the vehicle and didnt have any luck. Also tried using the "factory" timing marks that are on the crackshaft and cam gear and that also did not work. It would turn over smoothly, but not start. I moved the crank several notches either forward or backward from the factory timing mark and was able to get it started a couple of times, but it ran like crap. My cam gear timing mark is being placed at the 9 o'clock position, and the smaller pulley to the right of the crankshaft is being placed at its factory timing mark (about 10 - 11 o'clock position). Any suggestions?

  2. #2


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    Download this manual, read... then take another crack at it.
    If you can subnet a class C, you'll be able to do this with the manual.

    http://www.onsiteconcrete.net/d-50/F...-1983-1993.zip

  3. #3

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    for the record, subnetting a class C was easier. but its finally fixed! the problem i was having is that i only snapped the large timing belt and never messed with the small one. Also, the factory timing marks were way off and i had to find TDC the old fashioned way. not to mention the cam gear mark was wrong as well.

  4. #4



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    It should have looked like this on the cam to head. The book is not clear on the mark. Bad drawing.

    Click image for larger version. 

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  5. #5



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    Make sure your distributor was at #1 piston plug wire. At TDC, the first piston, closest to you is No1. The 2 closest valve rockers are loose also to show a closed off cylinder. (meaning compression stroke #1 TDC)

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    Ok, it more like setting up a OSPF route reflector, but you got it done...

  7. #7

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    I had a similar issue so I dove into mine today. When I cracked open the timing belt cover I discovered that not only had my balance shaft belt broken but the crank pulley had eaten about 8 cogs away off my timing belt so it was spinning freely.. After taking off the timing belt I turned all the pulleys just to get a feel for things and see if anything had ceased up causing the timing belt to lose it's cogs. Everything spun pretty well except for the cam pulley.. It spun but to me it didn't seem well lubricated/as smooth as it should. This is the first time I have ever done anything on an engine besides cold air intake, headers, and pulley kits so I'm pretty much just taking educated guesses on most the stuff I did today. So my question is about how tight is the cam pulley supposed to be when you rotate it with a wrench? Anyways, I figured with all the cam lobes being under a lot of pressure from the valve springs and such it would be pretty tight so I decided to throw on a new timing belt and give it a try. The truck fired up and ran for about 20 seconds then the belt slipped (due to my crappy tensioning job). Is there any common reasons why my cam pulley could be rotating tighter than normal? Or should I just do a better tensioning job and hope my timing belt doesn't get it's cogs eaten again?? Thanks in advance for any pointers putting me in the right direction!

  8. #8



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    The valve springs will make it jump between movements. Be sure to get the correct belt. There are 2 different types. one with rounded ribs the other with flat ribs. It makes a difference. There was another thread on here about that type of problem. One would work the other would eat up belts because of the pulleys. So look at the two belts and make sure they have the same cog types.
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  9. #9

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    Quote Originally Posted by camoit View Post
    The valve springs will make it jump between movements. Be sure to get the correct belt. There are 2 different types. one with rounded ribs the other with flat ribs. It makes a difference. There was another thread on here about that type of problem. One would work the other would eat up belts because of the pulleys. So look at the two belts and make sure they have the same cog types.
    shoot I def have the wrong belt then.. I got the one with round cogs. I noticed that but didn't think it could be wrong since I put in the right engine code etc. Is there any way my upper end isn't being lubricated properly? Also since the old cogs stripped out I figured the there is a problem that lies deeper than just the timing belt. The upper end still just seems too rough. Idk maybe it's just because it hasn't really run in a half a year or so and hasn't been fully lubed in a while ha. Thanks for the tip on the cogs though.

  10. #10



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    These are the Mitsubishi Manufacture Part numbers for the timing belts up to 1989 Mitsubishi Mighty max as you see below.
    Now, depending on your production month, which I do not know at this time for sure... this is the info I came up with. I might do better with a VIN number to find the part number specifically for a square cog belt, but not positive it will change much.
    Click image for larger version. 

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    PNC 03110 BELT, VALVE TIMING K02T

    4CA/T 1986.05.1 to 1988.09.3 / applicable models
    MD102249 old#
    MD140228 new#

    5FM/T 1986.05.1 to 1988.09.3 / applicable models
    MD113790 old#
    MD140228 new#

    1988.10.1 to 1989.05.3 / All Models
    MD140228

    Your going to find it incredibly harder and harder to find the square cog belts for the trucks. Companies are producing the basic style belts and very few go farther then this. The 2 types of belts for our trucks are as follows...

    Modified Curvilinear : This is the semi-round cog belts apparently you have purchased and are not fitting as you like.
    Click image for larger version. 

Name:	round cog.jpg 
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    Synchronous : This is the more square design cog which I think your searching for.
    Click image for larger version. 

Name:	Gates.jpg 
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ID:	6755


    Below is an image of 2 types of cam sprocket timing gears for the G63's. These are the 1st Gen and 2nd Gen Cam sprockets and the one on the right top is on a 1st Gen G63B engine. The one on left is off a 4G63 engine. Identical in all the perspectives except one, they are not interchangeable like I thought at one time. This is sort of a hidden issue between the G63B and the 463B engines. Now your truck has a square cog belt according to you. Your cam sprocket is identical to the one on the left if I am correct.
    All the other sprockets in the 4G63 are interchangeable with the G63B engines, but this one cam sprocket is the only one that isn't. I know this to be true because I have interchanged all the sprockets except the cam sprocket.
    Click image for larger version. 

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    Now, your looking for a square cog timing belt and your having problems. Well, we know all the other sprockets fit among the two engines and though they look square, they will also use both style belts. This being the Modified Curvilinear and the Synchronous belts. They rounded the edges on the belts to about 39 degrees If I remember right so that they slide into the cogs better and probably are just a bit quieter then the square looking belts. Now if you want to find the square cog belt, well I mean a less rounded cog, your going to have to order probably from Gates. Personally I would call them and talk to them on the phone about your issue. Gates (Power Grip) would be your best bet to get it right since they are huge and make belts for a living. Remember, you want a Synchronous or NON-Modified Curvilinear belt.

    Further Belt Specs:
    122 teeth
    3/4 inch wide / 19.05mm
    45 3/4 in. length

  11. #11

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    Quote Originally Posted by BradMph View Post
    These are the Mitsubishi Manufacture Part numbers for the timing belts up to 1989 Mitsubishi Mighty max as you see below.
    Now, depending on your production month, which I do not know at this time for sure... this is the info I came up with. I might do better with a VIN number to find the part number specifically for a square cog belt, but not positive it will change much.
    Click image for larger version. 

Name:	diagram.gif 
Views:	1795 
Size:	19.5 KB 
ID:	6756
    PNC 03110 BELT, VALVE TIMING K02T

    4CA/T 1986.05.1 to 1988.09.3 / applicable models
    MD102249 old#
    MD140228 new#

    5FM/T 1986.05.1 to 1988.09.3 / applicable models
    MD113790 old#
    MD140228 new#

    1988.10.1 to 1989.05.3 / All Models
    MD140228

    Your going to find it incredibly harder and harder to find the square cog belts for the trucks. Companies are producing the basic style belts and very few go farther then this. The 2 types of belts for our trucks are as follows...

    Modified Curvilinear : This is the semi-round cog belts apparently you have purchased and are not fitting as you like.
    Click image for larger version. 

Name:	round cog.jpg 
Views:	147 
Size:	24.5 KB 
ID:	6754
    Synchronous : This is the more square design cog which I think your searching for.
    Click image for larger version. 

Name:	Gates.jpg 
Views:	166 
Size:	61.9 KB 
ID:	6755


    Below is an image of 2 types of cam sprocket timing gears for the G63's. These are the 1st Gen and 2nd Gen Cam sprockets and the one on the right top is on a 1st Gen G63B engine. The one on left is off a 4G63 engine. Identical in all the perspectives except one, they are not interchangeable like I thought at one time. This is sort of a hidden issue between the G63B and the 463B engines. Now your truck has a square cog belt according to you. Your cam sprocket is identical to the one on the left if I am correct.
    All the other sprockets in the 4G63 are interchangeable with the G63B engines, but this one cam sprocket is the only one that isn't. I know this to be true because I have interchanged all the sprockets except the cam sprocket.
    Click image for larger version. 

Name:	sprocket3.jpg 
Views:	753 
Size:	84.0 KB 
ID:	6757
    Now, your looking for a square cog timing belt and your having problems. Well, we know all the other sprockets fit among the two engines and though they look square, they will also use both style belts. This being the Modified Curvilinear and the Synchronous belts. They rounded the edges on the belts to about 39 degrees If I remember right so that they slide into the cogs better and probably are just a bit quieter then the square looking belts. Now if you want to find the square cog belt, well I mean a less rounded cog, your going to have to order probably from Gates. Personally I would call them and talk to them on the phone about your issue. Gates (Power Grip) would be your best bet to get it right since they are huge and make belts for a living. Remember, you want a Synchronous or NON-Modified Curvilinear belt.

    Further Belt Specs:
    122 teeth
    3/4 inch wide / 19.05mm
    45 3/4 in. length

    WOW thanks for all that info! This will help me in the right direction. After looking at the pics you posted I am almost positive (without actually going to the shed and checking) that my cam drive is like the one pictured on the left with the four spoke pattern.. Which is a shame because it's not interchangeable.. So basically I'm stuck with going through hassle to find this belt if I ever need it again? No way for a conversion?

  12. #12



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    Get the gates belt that they have, Its called a Synchronous. If you buy another belt, the thing you need to make sure of is that it's not a Modified Curvilinear. Gates salesman will gladly help you out with your issue with atleast a part number, then google that number.
    You might try this... go to the dealer, ask the parts department to bring out both style belts. Make sure to get the part number off the square cog as you say. Once you have the CORRECT part number that is for your truck, google the part number. You will get several hits on the part number online. Find the cheapest priced and bada-bing, there you go. If you have a piece of your old belt or the old belt, look for a number on it maybe. Bring it to the dealer for example, some of them part guys only know software and were not even born in 1989, lol.

    The parts are out there, you have to do some searching...RockAuto can help too. Click the details on the items you choose for your truck and then call the company if needed. Don't give up and don't listen to some tird head on a phone that says there is no such thing either.

  13. #13

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    Quote Originally Posted by mcnunzio View Post
    I had the timing belt snap while getting on the highway in my 87 mmax G63b, initially i was told this was an interference engine and that i was basically screwed. After long searching, blogging, and talking to some mmax folks i found out that it is not an interference engine.
    i thought our engines are interference types..

    so after u changed ur t-belt, engine runs fine? u didnt check for bent valves or other damage?
    if you can't dodge it, Ram it!

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