timing belt slip verification

[jrbach]

After a bad run on few rebuilt ecu units, where each time the car ran fine until the shoddy rebuilds acted-up, I just installed another rebuild. It ran through the warm-up cycle pretty good, but it was jumpy on the way down and couldn't find idle. In gear it was a little rough, but it seemed pretty steady. On the test-run it lacked power and the timing sounded off.

My eyes aren't as good as they used to be and I don't have the tools, so I had to take it to a local shop. I was told the timing belt slipped and was shown the timing marks. The cam sprocket marks weren't perfectly aligned (but pretty close) and the crank mark was off to the left of the scale (maybe 18 BTDC?). So I have a couple newb-questions I pray you will answer for me:

1) For purposes of belt-slip verification, it doesn't have to be at TDC of #1 for me to know the belt has indeed slipped given the location of the marks I noted, right?
2) The mechanic should have done a compression test before requesting I authorize him to reset the timing, right? I'd hate to pay for the timing reset only to find out it needs a valve job too.

Thanks for the help

 

[beniger]

Yeah the marks, when in time, line up with the head. You also have to remember that there are 3 turns in the system, when the exhaust valves are open, when the intake valves are open, then when none are open spin. Crank at the crank more than once to insure that it really is aligned and not slipped. Compression check is to see if any valves bent if they indeed hit the piston.

 

[#40Fan]

Only proper way to do a compression test is to have the timing belt aligned correctly.

 

[trevor425]

ive found that judging the true crank position bye the crank pulley timing marks can be deceiving, its best to remove the pulley and the covers to acually line all the engraved marks on the cam gears and crank gear, as well as the balance and oil pump gears. also if the belt did indeed slip, its best to replace it and the tensinor, after first running a leak down test to check for any bent valves.

personally i always do a leak down test prior to replacing the t-belt if the belt has skipped teeth. it makes more sence for me and the customer, sence i would just have to redo the t-belt to remove the head and it wouldnt be right to charge for labor two times when it could of been caught beforehand. you can do a leak down test with the belt off btw. as long as the valves are closed, the cylinder should seal. with the leakdown test, u fill the cylinders full of compressed air rather then cranking the engine and relying on the cam and crank timing.

 

[beniger]

+1 on the leak test

 

[jrbach]

Thanks beniger...not too sure about that answer to my 1st question though. I'm familiar with the basic concept of the 4-stroke engine (intake, compression, power, exhaust).
The car is at the mechanic's shop. They aren't going to allow me to fiddle with the car, ok?
Again...I can only see the three marks I listed. The cam sprocket marks are very close, but the crank pulley mark is ~18 BTDC (off to the left of the tab somewhat). I do NOT KNOW if it's at TDC #1, or whether it even has to be to determine if the belt has slipped/jumped a tooth.
With that information alone, which is all I have, can I trust the mechanic that the timing belt has indeed slipped/jumped a tooth?

Thanks #40fan...I can appreciate that some of the valves might be open a bit if the timing is off. So I should pay for the timing reset and then find out if any of the valves are knackered?? The reason I'm asking is because if it needs valve work...the initial cost for the timing reset will be a total loss.

Sorry guys...I type real sloooow.

Thanks Trevor425! That makes more sense to me. Once they get the covers off though (you know, to be sure)...I'm pretty much in for the full amount. The belt has about 12k on it at the most, but the car's been sitting a lot for several years.

I'm sure I meant to say leak test rather than compression...thanks guys!
I'll be sure they've done the leak tests and then request I get to see how it looks with ALL the marks lined up before they start replacing those parts.

 

[trevor425]

im willing to bet the hydraulic tensioner has failed if the belt is that new and the car has been sitting unstarted for some time.
if the car is still running, you could likely get away with just a tensioner and re installing the current belt, but a leak down test should only take a good tech less then 30mins to do properly. and a new belt is cheap insurance.
good luck, i hope for the best dude.

 

[DroopYeyeS]

To your first question OP, The timing marks you can see with covers on only serve to show if the cams have slipped. Unfortunately the crank can indeed slip and not change the cam marks. The only way to be sure is with the front cover off and see all of the timing marks. Also, most reputable shops will not charge you twice for the work. If the timing correction fixes your problem you will pay that rate. If they end up needing to do head work, then the timing is built into the R&R hours for that job.
On your second question, A compression test, not a leak down test, would be the correct way to check the valve issue. However, #40Fan was correct about the timing having to be correct before this can be done. A leak down test is used to address issues with the rings. The oil used in a leak down seal the rings better to bring compression up. This helps to messure how much compression is lost past the rings.
Hope all goes well on this for you.

 

[trevor425]

To your first question OP, The timing marks you can see with covers on only serve to show if the cams have slipped. Unfortunately the crank can indeed slip and not change the cam marks. The only way to be sure is with the front cover off and see all of the timing marks. Also, most reputable shops will not charge you twice for the work. If the timing correction fixes your problem you will pay that rate. If they end up needing to do head work, then the timing is built into the R&R hours for that job.
On your second question, A compression test, not a leak down test, would be the correct way to check the valve issue. However, #40Fan was correct about the timing having to be correct before this can be done. A leak down test is used to address issues with the rings. The oil used in a leak down seal the rings better to bring compression up. This helps to messure how much compression is lost past the rings.
Hope all goes well on this for you.

an actual leakage tester uses compressed air through the spark plug hole while you rotate the cams slowly to bring them closed, no oil is involved.
using this method saves time and money since the engine isnt running and the timing doesn't have to be reset to check valve leakage/damage.

 

[DroopYeyeS]

Are u trying to say do a compression test with out the Tbelt on? This could be done of course as all the valves would stay closed when the cylinder builds pressure. How ever that is not a leak down test. I think I get what you're trying to get at here. For the op's needs, it still puts him at the t-belt coming off either way. If this were done with the belt on you'd be changing the volume in the cylinder with every rotation, looking for the phase when both the intake and exhaust ports are closed. Takes a lot of time to go through that for each cylinder. It could technically be done though. I know at my shop we wouldn't use that procedure. At any rate I hope the info we've laid out for you helps with your issue OP.

 

[jrbach]

Some members don't return to give an update...
Thanks for all the suggestions and info. I was pretty much at the mercy of chance and the shop's honesty. As luck would have it, both were positive.

The timing belt had been changed back when the recall caught up with me, but the dealer didn't do the balancer belt though...which was the culprit. It went out and luckily only caused a minor jump of the timing belt, which from what I read here before posting this thread...can be disasterous. It was worth it to find a good/honest mechanic, quite close to where I live, for the jobs I consider a major pain.
Thanks again...

 

[DroopYeyeS]

Good to hear sir! Mark thread resolved.