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I Think I've Messed Up My Timing Belt Change

mistermeena

By mistermeena,
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mistermeena Enthusiast

mistermeena

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I don't think it would be 180 out because even though we didn't line up the bottom mark, we were still careful not to move anything during the process. I'm just concerned that something might have turned a tooth or two while struggling with putting the belt on.

mad082 Grand Master

mad082

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It just makes it hard to align the marks, as the slack is on the wrong side. Cam timing is important to get right.

I saw an RB26 actually running backwards the other day, both cams were 90 degrees out, set up like Toyota cam wheels accidentally. Exhaust was coming out the airbox and fresh air sucking in the exhaust. Once the marks were realigned properly it ran fine, didn't even bend a valve.

Was it actually running, or just being turned over? Cause if it was running, where was the fuel coming from? Injectors in the exhaust manifold?

And the engine itself would've still been turning the same way as normal, since the starter motor determines which way the engine goes..... unless you roll start it down a hill going backwards in a forwards gear (but then there's the whole lack of fuel issue to keep it running)

scotty nm35 Grand Master

scotty nm35

Posted
Posted

The fuel was flowing into the open intake valve of course, then on ignition it would push the engine backwards. Basic physics Marc, believe what you like. (The timing was 180 degrees out to get it to run.)

It ran for 30 seconds like this, a few times. Not just a backfire, actually running in reverse, exhaust/fuel flowing out the plenum. Amazing there was no damage done at all.

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GTRPSI Mentor

GTRPSI

Posted
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Amazing there was no damage done at all.

Compression was tested and perfect after cam gears were repositioned, dyno tune was done and it produced some excellent results.

Its just that the owner couldn't help himself giving it the beans with the antilag and blew the new clutch before he had bedded it in. LOL

I didnt see them trying to start it but yes could have run backwards......cas position would have been 90 degrees out too.

mad082 Grand Master

mad082

Posted
Posted

The fuel was flowing into the open intake valve of course, then on ignition it would push the engine backwards. Basic physics Marc, believe what you like. (The timing was 180 degrees out to get it to run.)

It ran for 30 seconds like this, a few times. Not just a backfire, actually running in reverse, exhaust/fuel flowing out the plenum. Amazing there was no damage done at all.

yes, basic physics. You said that fuel and exhaust coming out of the intake. why? Because on the exhaust stoke gases come out of the engine, and since the intake manifold was acting as an exhaust, fuel being fired into the manifold gets blown away from the valves, not sucked into the engine.

Not to mention the damage to the starter motor having an engine trying to fire in the opposite direction to the way it was being turned.

Now I'd certainly believe the timing being out far enough to have some cylinders being out of sync to have the intake valves open on the exhaust stoke, but certainly not all of them because that isn't possible. Why isn't it possible? Because as I explained, if all the fuel is being blown out the intake then none is getting into the engine to make it fire. And fuel being blown back out the intake doesn't mean the engine is running in reverse, simply that the timing is way out.

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scotty nm35 Grand Master

scotty nm35

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The fuel was on the back of the valve and ran down into the bore when the valve opened. What is so hard to understand that you need to argue about it? I was just telling it how it happened, no need to try and disprove it, I could replicate it on your rb if you had one.

Fact was it ran backwards, no amount of moderating will change that fact Marc. And no damage was done to the valve train or starter motor.

533 RYC Proficient

533 RYC

Posted
Posted

yes, basic physics. You said that fuel and exhaust coming out of the intake. why? Because on the exhaust stoke gases come out of the engine, and since the intake manifold was acting as an exhaust, fuel being fired into the manifold gets blown away from the valves, not sucked into the engine.

Not to mention the damage to the starter motor having an engine trying to fire in the opposite direction to the way it was being turned.

Now I'd certainly believe the timing being out far enough to have some cylinders being out of sync to have the intake valves open on the exhaust stoke, but certainly not all of them because that isn't possible. Why isn't it possible? Because as I explained, if all the fuel is being blown out the intake then none is getting into the engine to make it fire. And fuel being blown back out the intake doesn't mean the engine is running in reverse, simply that the timing is way out.

Marc, there is a little thing commonly know as 'overlap or scavenge'. Most engines utilize this phase/process to facilitate getting exhaust gasses out quicker & getting a better cylinder fill. Nearly all camshafts have an overlap period.

So the intake & exhaust valves are open at the same time, to some degree. So it's completely plausible for an engine to run backwards depending on the overlap period & injection timing, & if it happens on 1 cylinder, it will happen on all. Mythbusters will confirm this.........

mad082 Grand Master

mad082

Posted
Posted

The fact that has been ignored by everyone but me is the starter motor. The starter motor spins the engine at a few hundred rpm, and you don't actually stop the starter turning the engine over (by releasing the key) until you hear it come to life. So for the engine to run in reverse it would either have the shear the teeth off the starter motor, or start running forward and then backfire so severely as to be able to make the engine run in reverse.

Look, I'm not really debating the fact that the engine ran with the cams 90 degrees out, because I'm sure it probably could (despite how my previous posts might imply). What I will debate though is the fact that the engine was running in reverse because of it. As I said above, the starter motor determines which way the engine spins, and just because exhaust gases are coming out the intake doesn't mean that it's running backwards, simply that the timing is way out (as I said in a previous post)

scotty nm35 Grand Master

scotty nm35

Posted
Posted

The fact that has been ignored by everyone but me is the starter motor. The starter motor spins the engine at a few hundred rpm, and you don't actually stop the starter turning the engine over (by releasing the key) until you hear it come to life. So for the engine to run in reverse it would either have the shear the teeth off the starter motor, or start running forward and then backfire so severely as to be able to make the engine run in reverse.

Look, I'm not really debating the fact that the engine ran with the cams 90 degrees out, because I'm sure it probably could (despite how my previous posts might imply). What I will debate though is the fact that the engine was running in reverse because of it. As I said above, the starter motor determines which way the engine spins, and just because exhaust gases are coming out the intake doesn't mean that it's running backwards, simply that the timing is way out (as I said in a previous post)

Its only a 12V motor, it won't put up much of a fight over the power of the engine...

It ran backwards, exhaust came out the air filter, then once we dropped the plenum hose, it dumped out there. There was nothing coming out the exhaust, and it was sucking air. If you would like to disprove me you will need something better than that...

I have a fairly extensive knowledge mechanically and know exactly what and how it happened, I was just sharing my experience, as I had never seen it before.

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mad082 Grand Master

mad082

Posted
Posted

And as I've said multiple times, just because exhaust came out the intake doesn't mean the crank was moving in reverse. It means the timing was out by 90 degrees per cam, as you have said in your original post, as this has the exhaust cam opening on the up stroke of the piston instead of the down stroke. If the engine was running in reverse it would actually be sucking air in through the intake at this point, not blowing it out.

For the engine to be spinning in reverse and having the exhaust come out the intake, the timing would have to be setup normal, or 180 degrees out per cam, however this wouldn't actually result in any issues with running (since every second rotation of the crank puts the cams at 180 degrees out, since the crank turns twice for every rotation of the cams), so it would run in the normal direction thanks to the starter motor. If I get some spare time at all I could make a basic animation showing valves opening and crank/piston direction and position proving I'm right if you like.

As for the starter motor just being a weak 12v motor, try putting a manual car in gear, put your foot on the brake and then try starting the car and see just how weak that motor is. I'd suggest not doing while in your garage unless you like having the car inside your house......

scotty nm35 Grand Master

scotty nm35

Posted
Posted

just because exhaust came out the intake doesn't mean the crank was moving in reverse.

Flowing in reverse at least. I obviously didn't check the crank direction of travel as I had more important things to worry about, and really, I don't care as it's fixed.

You argue more than my missus.

mistermeena Enthusiast

mistermeena

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Posted (edited)

so finally had a chance to sort this out today. Lined up the bottom mark and confirmed cyl 1 was at the top, and found that the cam gears were each out by a tooth. We adjusted the cams to make it all line up and turned it over by hand through a few cycles and they continued to line up on every second pass so I think that's all ok now.

I'm still a bit unsure about setting the tensioner. I left it finger tight while I turned the motor over 3 or 4 times, then tightened the nut on the tensioner with the motor back at tdc. Is that correct?

Edited by mistermeena
GTRPSI Mentor

GTRPSI

Posted
Posted

Flowing in reverse at least. I obviously didn't check the crank direction of travel as I had more important things to worry about, and really, I don't care as it's fixed.

You argue more than my missus.

Yep, my feeling is it may have just been backfire or combustion leaving the intake side.

If it did fire backwards while starter was cranking it would have just stopped the engine and not damaged the starter, seen and built heaps of old school dizzy engines, too much timing and it just wont crank, acts like a dead battery, starter cant push against it, wont spin backwards. (or didnt on the ones i did)

Can we change the subject now? :)

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