Broken Timing belt tensioner job gone bad... - Honda Prelude Forum

chris.s · 02-06-2008, 09:11 PM

Ok, so my friends 98 prelude's timing belt tensioner failed. This was somewhat confirmed by pulling the valve cover and seeing the slack belt. I was just thankful that the belt was still in one piece. I was worried about some serious damage since the engine was running and started twice since the belt started flapping inside the cover. So after some reading through these forums and the FSM i started at it.

So the usual process, remove the accessories, brackets, 3 days fighting the crank bolt, timing belt cover and pulley etc

I have run into a very odd/disturbing situation, the crank sprocket timing marks do not match the engine plate (flywheel) marks, and by not matching, I mean WAY OFF!! Before I started I set the engine to No.1 TDC using the timing mark on the flywheel. the problem is that after pulling the crank bolt/pulley I see that the TDC marks are not aligned as expected.

See pics...
note that these are taken together without moving either of the cams or the crank(the cam pic is showing the belt still on, but this is the position they were in when the belt was removed)

The initial assessment was that we may just get away with a belt/tensioner since it looked like the cams didnt skip too much (maybe the intake cam went off 2-3 teeth). But this whole gross misalignment between the two TDC marks makes me suspect the worse.

Anyone ever run into this?

The way I see it, there are 2 possibilities
-Broken crank, would explain why the TDC on the flywheel and the timing sprocket are off by ~30 deg.
-Someone previously was working on the trans/flywheel and didn't put the engine plate back on properly (is this even possible? I assume it is keyed for timing light purposes) in this case the pics of the cams would indicate that they are WAY off (jumped multiple times) and I might be looking at new valves or a replacement head.

Either case spells disaster....

I just have no idea what to make of the timing marks not matching up on either side of the crank. Oh, and for what its worth, with the crank set to TDC (referencing the flywheel marks) I tried to check the position of the cylinders, I was able to feel the position of No 1 and No 4 bu using a straw, both 1 and 4 are at the same height pretty close to the bottom of the head) I dont want to move the crank solo too much since the belt is off, and I'm worried about causing more damage by not turning the crank+cams together.

any thoughts?

Keith · 02-06-2008, 10:39 PM

Looks like the crank slipped on the timing belt... better get it lined up and then do a compression check.

Keith

chris.s · 02-07-2008, 04:59 AM

Right.
But how then do i explain the fact that if i were to move the crank to TDC, that the TDC mark on the flywheel would be way off. Check the pic of the crank sprocket, its about 40 deg from TDC, but the flywheel says its pretty much bang on already.

chris.s · 02-07-2008, 08:49 AM

So as a follow up, I just spoke with the Service advisor at the honda desk about this. He said that the engine plate/flywheel marks are NOT keyed to only fit one way. This seems suspecious, since this is the only reference one has to use to check the timing without removing the valvecover. can anyone confirm that the timing/engine plate is not keyed to only fit on one way?

basically he recommended confirming TDC as marked on the timing side of the crank/sproket with a feeler in piston 1+4, apparently they move in unison. Also he mentioned that I should not be able to bend any valves (if not damaged already) by rotating the crank by hand.

BBYlude · 02-07-2008, 09:10 AM

You certainly can find TDC on any cylinder with a feeler, and yeah, if any valves are already bent, and the belt hasn't slipped any further, you shouldn't further damage the valvetrain.

If you pull the camshafts out, the valves will all return to fully closed. This will allow you to rotate the crank assembly without any risk (I don't feel there is any though), as well as doing a bleed-down test on each cylinder w/o having to rotate the head assembly for each cylinder test.

So you'd pull the cams out, fix the tensioner issue, check the valvetrain (fix if necessary), find TDC on cylinder#1, re-install the cams using alignment marks (the cam alignment tool will help you a lot), and re-install the timing belt.

Also, all four cylinders do not run in unison, they run in pairs (1/4 and 2/3) For example: Both pairs run in unison(sp?), but on different strokes; when cylinder one is on its compression stroke, cylinder four is on its exhaust stroke. When cylinder two is on its intake stroke, cylinder three is on its firing stroke.

chris.s · 02-28-2008, 08:26 PM

Thanks for the replies.

I did a leak down test and No.4 is leaking badly out of both intake and exhaust (no pressure build up). I verified that it was in fact leaking multiple times before and after removing the cam shafts. I even tapping the top of the lifter (with socket and robber hammer) but it didnt change anything.

So I pulled the head off expecting to see a bent valve, but all I can see is that there is alot of buildup on all of the valves. The valves that are leaking seem to be sitting the same as the rest. I guess it might not take much distortion in the actual valve stem to cause all of the compression to be lost.

Anyways, the head is going to be swapped out and none of the pistons seem to be damaged. There is a thick carbon buildup on all of the piston heads, looks almost like 60 grit sandpaper. The walls of 3 and 2 looks nice and clean, i havent rotated the crank since there was alot of carbon debris i wanted to clean out first. Im just glad the piston surface is intact.

I removed the head and intake manifold as one (per the fsm). Anyone ever remove/install the intake manifold by it self? How difficult are the bottom bolts to access? I would prefer to install the head and then install the intake manifold if possible.

Solid · 02-28-2008, 09:07 PM

At Honda they usually put a head back on with the IM connected. Doing the IM after wards is a pain since the firewall is so close to it and you won't get much room to work with.