Oh no... timing belt riddle!

[chasesmr2]

Seriously, my son just bought a nice used 87 mr2 with 1600cc motor (I think 1594 actually. The guy he bought it from said it had been rebuilt 14,000 miles ago.

My son drove it about 100 miles and the engine suddenly stalled and won't restart.

Fuel is fine, spark is fine, so I took it to my mechanic and he said compression is low (50psi) on all 4 cylinders. Strange... I suspected the guy lied to us until I took the pan off and saw the bottom of the cylinder bores looked nice.

So next I wanted to look at the valves... but in lining up the camshaft timing marks to remove the timing belt, I was spinning the crankshaft and noticed that it took about 30 degrees of motion before the cam sprockets started moving.... really strange!

Belt looks fine, no teeth missing and the belt tension was OK. The weird part is that the cam belt pulley sprocket down on the crank has about 30 degrees of "play" in it. This is where the delay in the camshafts is coming from.

So the question is, is this normal on these motors or should it be ridgidly mounted as all other motors I've worked on are. If it isn't normal I believe that the valves are not in time with the compression stroke and bleeding off compression by not being fully closed at the appropriate time.

Don't worry, I checked the top of the pistons and there are no marks from a collision with the valves. Valve stems are also straight.

Thanks, Chase

[MR2Jedi]

I don't own a gen 1 MR2, but I don't think there should be any play/slack in the belt tension. (with any vehical with a timing belt)
Does it have a tensioner?
Another member on this forum-ModifierMR is very good with the AW11. Hopefully he will chime in on this .

[chasesmr2]

Yes, it has a tensioner and it was working... the belt was nice and tight before I started taking it off. That's when I noticed all this slop in the cam belt pulley down on the crank. Almost appears as if a pin or key came out of a keyway. Anyone else know for sure if there should be any "backlash" in this pulley or should it be tight.

Thanks, Chase

[toyomoho]

The crank pulley is usually pinned to the crank via a key. Try rotating the pulley by hand to see if it is turns without moving the crank, do the same with the cam pulleys. Guessing the key is partly sheared or slot in the pully damaged.

[82toyo]

I would have to second the key being broken-they have a tendancy to do that. Bad part is that the shaft may be damaged also. Let us know what you find out.

[chasesmr2]

Hi everyone,

Just an update to what I found. Got the accessory pulley off the crankshaft and then slide the cam pulley off. Well... you guys were right, the key was pretty chewed up and that in turn wallowed out the cam pulley on the crank really bad. Luckily it didn't damage the crankshaft! Interestly, the key is one of those half-moon shaped affairs and it only extends about half way into both the accessory pulley then into the cam pulley. They should have made it full width but anyway, I think we found the reason for the compression loss... bad cam timing! Thanks for everyones help!

Chase

[toyotaspeed90]

the tensioner is NOT a moving tensioner while the engine is running.... the tensioner is purely for putting the belt on and ensuring there is tension on the belt... there should be a bolt going through the center of the tensioner that should be tightened down....

almost sounds like it jumped timing.... i've had (an seen) 4ag timing belt tensioners lose the bolt and jump timing.... pull off the remaining dust covers, motor mount, and crank pulley, replace the belt and see what happens.... they're only like $15 and not too difficult to change.

make SURE you mark which timing gear goes to intake and which exhaust if you pull them off... they look identical but do not go on the same

[chasesmr2]

Thanks for the additional hints... but just to make sure everyone understands what happened, it was the camshaft belt drive pulley on the end of crankshaft that is damaged. The tensioner is a separate pulley and it was tight and in good shape. The pulley that is damaged is keyed to the crankshaft and this keyway in the pulley as well as the key, were pretty chewed up.

By the way, I hate all this electronic ignition and fuel injection. We are seriously thinking of stripping everything electronic ignition and electronic fuel injection off the motor and making the whole thing really simple.

A pair of Weber 45 sidedrafts for fuel delivery (about $800) and MSD 6 for ignition. We are thinking of making the car a track car only... perhaps SCCA production classes. Kind of like a formula atlantic motor only staying below 160 HP. We don't want to do an engine swap to the supercharged motor and like the look of the Weber's. Is the ECU going to try to interfer with my plans?!

Thanks, Chase