Hello fellow DSM'ers. So 3 months ago my fully built English Racing long block snapped its timing belt after only 20k miles.

So with no help coming from English (I tried), I had the head rebuilt with new valves by Garage 808 (local shop) and did the rest of the work myself. (for more on that subject and why I think English should have stood up and helped me fix this, see my build journal and feel free to comment after reading post #226. http://www.dsmtuners.com/threads/97-gsx-build.419169/page-10)

Anyways,... during disassembly I inspected the timing belt cover and you can see how the timing belt walked over and into the timing cover. (pics below) Oh and what looks like dirt is actually plastic/belt particles (only 20k miles ago this cover was brand new and installed by English Racing.)

This next picture is the part of the cover that goes over the oil pump sprocket.

When inspecting the snapped belt it has three other spots where it was starting to rip across the belt, all of these spots are on the timing belt cover side, the engine side of the belt looked great with no wear.






So here I am at this point where I have the car back together and running well again and have put 50 miles on the car and am loving having my car back! (haven't hit boost yet thou I'm scared ). I am worried about this timing belt snapping again as I don't really know why it happened in the first place, and also I don't want this one to snap resulting in a head rebuilt or worse, again haha...

So last night I investigated,... I took the timing cover off just to take a close look at all the timing components. Everything looked fine except I did notice that the belt is riding on the very outside edge of the idler pulley. Looking at the picture below you can clearly see where the belt rides on the idler pulley.


So then I looked down at the oil pump sprocket... It has a big metal washer thing to guide the belt? Well I think that the belt is rubbing on that metal guide washer as you can see some of the oil sprocket gear on the engine side but not on the other side as the belt is right up against the "washer guide". The belt is centered nicely on the cam gears, the tensioner pulley, and the crank sprocket. It's just not centered on the idler pulley and oil pump sprocket...The idler pulley, tensioner pulley, hydraulic tensioner, timing belt and even the arm that the hydraulic tensioner pushes onto that has the pivot point on the motor mount bracket are all brand new OEM Mitsubishi parts. From this detailed post I would really appreciate any help/advise/experience you can give me on why this belt is not centered on the idler and oil pump sprockets. Thanks for your time, -Matthew

-Also looking at the damage on the timing belt cover I can't see how the belt was able to hit the cover that much unless the belt actually went over that metal washer lip edge!? that has me very worried. Please any help would help me big time.

Bummer on the failure.
Its been a while since I've set a timing belt, so bear with me. If I remember correctly, the crank stack-up has the CAS plate in the stack, make sure this stack is correctly assembled and not pushing the belt. Kevlar belts are expensive... but reaaaalllly cheap compared with problems from failures.

The belt follows the perfectly aligned sprockets. Your crank is aligned by bearings, as are your cams (straight). The idler pulley axis is aligned by the clamp to block. Oil pump axis aligned by bolt/pump housing. The long shafts (crank/cams) are likely to be perfectly aligned as long as the mating surfaces to sprockets don't have rust or something which will skew the rotation axis. The oil pump and idler pulley are a bid more susceptible to a skew. Watch your rotating assembly while it is running for any "wobble." I'm not saying this is the issue... but it seems the root cause is still out there. Broken cords on the belt will cause the belt to bias in or out.

Everything perfect, (including belt) the belt should track.... essentially... something is not perfectly aligned or the belt was not right.

Man where are all u guys coming from? we have to have a local meet soon

That sucks, we know a thing or two about failures... Luckily on the 2.4 it is non interference.

Sometimes its good to have no upper timing cover either

Were the tensioners working? A bad tensioner leads to this sort of thing inadvertently sometimes.

Only thing that really got changed was the adjustable cam sprockets.

Wonder if those sprockets didn't get aligned correctly with the crank sprocket pulling the belt out of alignment around the oil pump sprocket.

at least i know who isnt going to be building my engine

bjones18 said:

Bummer on the failure.
Its been a while since I've set a timing belt, so bear with me. If I remember correctly, the crank stack-up has the CAS plate in the stack, make sure this stack is correctly assembled and not pushing the belt. Kevlar belts are expensive... but reaaaalllly cheap compared with problems from failures.

The belt follows the perfectly aligned sprockets. Your crank is aligned by bearings, as are your cams (straight). The idler pulley axis is aligned by the clamp to block. Oil pump axis aligned by bolt/pump housing. The long shafts (crank/cams) are likely to be perfectly aligned as long as the mating surfaces to sprockets don't have rust or something which will skew the rotation axis. The oil pump and idler pulley are a bid more susceptible to a skew. Watch your rotating assembly while it is running for any "wobble." I'm not saying this is the issue... but it seems the root cause is still out there. Broken cords on the belt will cause the belt to bias in or out.

Everything perfect, (including belt) the belt should track.... essentially... something is not perfectly aligned or the belt was not right.

Click to expand...

Yea I thought about that, I was thinking that maybe the oil pump sprocket is moving out a bit from its center axis, but with the car running it looks good, I don't see any wobble. And when I had the belt off I tried to check for play on the oil pump sprocket but it seemed good to me.

darknezz7 said:

Man where are all u guys coming from? we have to have a local meet soon

That sucks, we know a thing or two about failures... Luckily on the 2.4 it is non interference.

Sometimes its good to have no upper timing cover either

Click to expand...

I have been here yo! DSM for life . We will have to meet up sometime. Yep upper timing cover is off and the belt will be inspected closely every oil change now .

jimsgsx said:

Were the tensioners working? A bad tensioner leads to this sort of thing inadvertently sometimes.

Click to expand...

The tensioners looked great, not leaking or anything, and the tensioner pulley was still set right after I removed the belt so it didn't loosen up or something.

DSM1G90 said:

Only thing that really got changed was the adjustable cam sprockets.

Wonder if those sprockets didn't get aligned correctly with the crank sprocket pulling the belt out of alignment around the oil pump sprocket.

Click to expand...

The adjustable cam sprockets have always been there. The belt rides in the center of the cam sprockets and the center of the crank sprocket, just not centered on the oil pump sprocket or idler pulley.

just not centered on the oil pump sprocket or idler pulley.

Click to expand...

Wonder if the idler pulley isn't square to the block then causing the mis-alignment.