Massive TB Failure 89 HC

[older929]

The timing belt snapped on my US 89 HC today. One edge (facing motor) looked like it got chewed up or caught on something and the belt was snapped. Under 50K on this belt. What could cause this kind of failure? I am replacing the belt, pulleys, tensioner wheel, hyd tensioner and Water pump. I there some kind of issue relative to the tensioner wheel install? Do I need a washer in back of it for some clearance issues or to help position it better on the hyd tensioner?? Are the two pulleys identical in size and function? The look the same to me. Where could I be having problems? This belt should not have snapped like this. Are there widely variable quality levels of timing belt? I'm not sure what this was, gates or dayco or something else.
Car has only 100K and should not be freaking out like this.
Help and guidance greatly appreciated.

[NoD]

Looking at the epc, tension pulley bolts to the block with some bushings, washers and spacers.
Part numbers indicate that the idler pulleys are identical.

Age of the belt will also play in.

Sometimes a new timing belt, from a good manufacturer just snaps. If it were me i would send the manufacturer a email.

[older929]

What's the epc? I think maybe I'm missing a washer on the tensioner wheel? Not sure and dont remember from last time I worked on this. I did see a comment on and ebay item about some kind of washer having to do with the lever for the tensioner wheel. Wonder if I dropped something before?

[NoD]

epc is short for electronic parts catalogue, just like the program they got at mazda dealers.

if you sign up at allmazda.net you can look at technical drawings and partnumbers.



Bolt, washer, bushing, tensioner, bushing, washer, spacer

[older929]

Hey, thanks very much!!! I'll start taking my tensioner apart to see if all the parts are actually there. Maybe there is a washer missing. I'm inclined to doubt that since it did manage 40K miles before the belt broke. I'm leaning to a water pump problem that may have damaged the belt last winter. The car had a very bad leak, looked like WP so I put it away for the winter. In the spring, no leak so I decided to wait until later in the summer to replace the WP for next winter. Guess I should have fixed it sooner. Engine will be OK though I think. I've blown belts on these motors a few times and never had broken valve issues. Thanks again, this is most useful.

[older929]

Thanks again for the EPC site!! That thing is great. I'm using it in conjunction with mazdapartscheap.com and finding everything. Wish I knew about this 10 years ago :-)

[older929]

EPC Question. I'm located in the US and have a US model 929. Under the HC designation there appear to be 2 classes of 929. EPC seems to be meant for Europe. I realize most hard parts shouldn't matter and in fact the P/N for the most part do show up at a US Mazda Dealer who sells parts on-line. I'm just wondering which flavor HC at EPC is most like the one Mazda sold in the US for 1989 Model year.
Thanks.

[NoD]

If yours was produced after the 6th month in 1989 then choose 1989. If it was produced before that then use 1986.

other than that there are some vin specific parts, especially in the transmission section, that you can use to pinpoint the production date.

[older929]

Originally Posted by NoD

If yours was produced after the 6th month in 1989 then choose 1989. If it was produced before that then use 1986.

other than that there are some vin specific parts, especially in the transmission section, that you can use to pinpoint the production date.

Well, sticker on the driver's door jamb says 12/88 so this must be an early one. My other 929, also an 89 shows the same 12/88 date. Serial number wise they could have both been built around the same time. I'm only buying bolts, and some odd misc parts. I think I'll be OK regardless. I'm going to do the complete TB/WP job including the hyd tensioner (expensive). Gates belt this time. Looks like the belt that broke was an ITM. Hard to tell what happened exactly. Looks like belt might have jumped and got cut by one of the idler wheels. no real wear patterns evident, just a snapped belt with a little slice on the side.