I put a JDM B20B into my 98 crv 11 months ago and replaced the timing belt tensioner water pump etc.

I did all of that work while the engine was out of the car before we dropped it in.

Anyways I was on a weekend trip and the timing belt snapped. It looks like something happened to really stress the belt and make it snap. We haven't fully got the head off yet or the timing belt cover off but from the looks of it and from first guessing the tensioner failed. Time will tell later this week when we can get in there and look at it but here's the pics of the damage.






what do you guys think caused this and how can I prevent this crap from happening again. Is this common? did I put it on too tight?

Also, should I try and locate a whole new engine or a head or have the head rebuilt?

 

Whatever the problem is I don’t know how you didn't catch that before hand.

In my opinion it looks like the tensioner seized and overheated the belt allowing it to snap. Even if you applied tension to tensioner with a screw driver you would only prematurely stretch the belt. The engine would have sounded like it had a supercharger on it though.

Due to your lack of commas I am not sure exactly what all you replaced. If you didn't replace the belt then that was wasted effort anyways. Also, with out you telling us exactly how you tensioned the belt, nobody will be able to tell you if you did it wrong.

The head could be fine or maybe just some bent valves if you are lucky. Why don't you pull the head and find out first?

 

yeah I replaced all of those parts including cam and crank seals.

I honestly do not remember how i tensioned it as It was a over a year ago and I did it when the engine was still sitting on the pallet.

I'm going to get the head off in the next couple of days and assess the damage. My guess is also that it was the tensioner I'm just wondering if maybe it was torqued down too hard on the bearing and caused it to fail prematurely. Time will tell but for right now I'm really not sure what the heck happened. By looking at the damage to the belt it seems like the tensioner is to blame.

 

I agree with the tensioner theory

 

we've decided to slap a new belt and tensioner on the engine once my crankshaft removal tool arrives. Worse case scenario the top end has bent valve and it wont run or run right. rebuilding the head or getting a new head and everything involved with it is just as costly as getting a whole new B20 so it's at a "lets see what happens phase". When it was turned over there was no audible sound of piston hitting valve so maybe I got lucky.

 

The glazing on the non-teeth side of the belt, including the scour marks do indicate a bad tensioner. But you will know when you open up the timing belt covers.

Always tension using the Honda tensioning method. It may seem like the belt 'will be too loose' based on their instructions, but a timing belt only needs to be tensioned enough so it doesn't jump teeth, not tensioned snug to the point where the bearings are always seeing high loading. I leave about 4-7 mm of slack on the non-tension side, depending on the car. I've done dozens of timing belts without issues on several makes.

Always buy a brand name belt/tensioner. I buy gates t-belt, tensioner and water pump kits from rockauto. I've never had a failure. Good luck. Hopefully the revs where nice and low when this happened and you don't have a damaged head.

 

Once valve damage is done, you won't hear anything. They only hit once.

 

it was on a snowy road going slow in 4th or 5th gear at best doing 2500rpm I might be okay. time will tell once the OEM tensioner and belt get in

 

You haven't dealt with broken belts before have you? Lol. You have roughly a .037% chance of no valve damage.

 

well regardless I'm going to have to buy a new belt and tensioner. I can't break it any worse than broke. worst case scenario i'm in the market for a rebuilt head.

I'll get the new belt on and run a leakdown and see where that gets me.

 

I can't see how that belt looked the way it did if you replaced it a yr ago. Unless you replaced it with another used one that is. I've looked at timing belts after a yr and they never look like that. They still look brand spanking new, as if I just bought that bitch from Honda, and only Honda, themselves.

Edit: I will say that your cams look good for the condition of the motor. It doesn't look dirty with burnt oil on there so you have a good motor.

Edit 2: Can you explain to me in detail how you tension your belt? There is a specific way of doing it.

 

A lot of times you wont get bent valves at mid to high throttle. It seems like you bend valves way more often at idle for whatever reason.

As far as the failure? Looks like a bad tensioner. Go OEM Honda here, the same for the waterpump.

 

Hopefully people will start to appreciate the fact that when it comes to maintenance parts like this OEM quality is the best. Not to mention if you order everything online its cheaper than dealership and is only a LITTLE BIT more than AUTOZONE, PEP BOYS, O REILY'S and NAPA parts.

 

I know for a fact I tensioned it too tight. The tensioner was fine when I pulled it.

So it had to be overtightening of the belt.

I used a OEM belt, pump, and tensioner when I did the job. But i'll be honest after reading into it further I definitely over tightened the belt. So it all rests on me.

 

To tension the belt correctly put the belt on, put a little tension on the tensioner, turn the engine over at least one full revolution counterclockwise to seat the belt. Then loosen the tensioner adjust bolt half a turn to a turn. With the engine at TDC turn the crankshaft with a bar or ratchet until 3 teeth have gone up on the intake cam pulley. Tighten the adjusting bolt. The belt will at times seem rather lose when turning the engine over by hand, this is normal.

 

If you say so. I have seen my fair share of over tightened timing belts - NONE of them looked like your belt let alone broke. Even the ones that came in with severe supercharger whines. Either way, glad you can admit fault.

 

yeah we tensioned it when it was on the crate. pretty sure from what i remember i pushed on the tensioner to make it super tight. big mistake.

here's the news after properly putting a belt on it and checking compression.

Cyl 4 185 psi

Cyl 3 160 psi

Cyl 2 185 psi

Cyl 1 190 psi


thats 160 really worries me. Is this too far out to even bother putting everything back together and actually starting it? I think they should all be fairly close right? that 20-30 psi difference seems big to me but I'm not sure.

 

not sure how good this harbor freight tester i got is but i cranked on it a little longer and cyl 3 showed 170 psi :-/

 

The numbers would tend to indicate a blown headgasket more than a bent valve. With a bent valve you'll get either no compression or very little in the affected cylinder(s). If it's a harbor freight tester I'd blame it on the tester first. I'd certainly try just putting the belt on with those numbers.

 

I agree; perhaps lady luck is on your side.

 

got the new parts on. ran the engine for about 10 seconds since the coolant was drained. it sounded fine. revd fine. time will tell when i get a longer run out of it but i suspect everything is okay. followed the correct timing belt tensioning method this time...