Can anyone help me PLEASE

I had my timming belt snap two weeks ago, after stipping down the head to access any damage and thinking i might get away with just replacing the push rods and fiiting a new belt. However for some reason the piston 1 is not at TDC when the fly wheel locking tool is engaged, also pistons 1 and 4 reach TDC at the same time as well as piston 2 and 3 reaching TDC at the same time when turning the crank. Does any one know what has happend and how to fix it as i understand the pistons should move in the firing sequence 1324.

bent cod rods

aaatreeclimber said:

I had my timming belt snap two weeks ago, after stipping down the head to access any damage and thinking i might get away with just replacing the push rods and fiiting a new belt. However for some reason the piston 1 is not at TDC when the fly wheel locking tool is engaged, also pistons 1 and 4 reach TDC at the same time as well as piston 2 and 3 reaching TDC at the same time when turning the crank. Does any one know what has happend and how to fix it as i understand the pistons should move in the firing sequence 1324.

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by "piston 1 is not at TDC when the fly wheel locking tool is engaged" - what do you mean? are pistons 1 & 4 coming up the same amount, or are they coming up different heights? How far up are they coming when the locking tool is engaged?

Are we sure that the timing pin locks it at tdc and not at safe?

You seem to have some confusion about the firing order - The first thing you need to understand is that the diesel engine is a 4 stroke power plant - so 1+4 will come up together, and 2+3 will come up together

When 1+4 and at TDC 1 will be on the exhaust cycle, and 3 will be on the compression of the fuel cyclea, or vice versa and the same for 2+3. The crank shaft is set 180 deg out and NOT 90 degrees out to allow for it to be easily ballanced and so the the ignition of 1 drives the compression or 3 and is then ready to fire as just as 1 is finishing is downward decent (ready to drive it back up again to cause the expulsion of the exhaust gasses on to the turbo etc, and to compress cylinder 4 as it comes back up.

If both pairs are comming up to the top together, and reaching the same height then there 'should' be nothing to worry about - if one is behind/lower than the other then the con rod is likely to be bent, and needs replacment. - Push rods are wonderful things ..................... (like fues)

Thanks so far. Using a smaller locking pin I have locked the fly wheel with the woodfuff key inalinement and piston 1 at TCD. Both piston 1 and 4 are at the same hight ( i cannot tell now much as the messurments on my feeler gages have faded.) Is this sounding right so far? :doh:

Ok starting to understand now (thanks james). So once pistons have reached TDC the next thing to happen is for the exhaust value to open as the piston moves down?

aaatreeclimber said:

Ok starting to understand now (thanks james). So once pistons have reached TDC the next thing to happen is for the exhaust value to open as the piston moves down?

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The cycle goes like this
1)Intake (Going Down) (intake valve open) - Air is forced in by the pressure in the inlet manifold being higher than that in the cylinder (as the space has increased) - The turbo and intercooler increase the inlet pressure above the atmospheric pressure causing a higher presure gradient.
2) Compression (both valves closed) - the piston moves back up compressing the air - fuel is also injected into the cylined by the fuel injectorjust before TDC - the exact timing is set by the injector pump - (what we refer to as the timing angle (what we wound advance or retard))

3) Ignition - the fuel ignites due to the high pressure and temp, forcing the piston back down.

4) exhaust (exhaust valve opens just as the piston is about to move back up allowing it to force the exhaust gases out into the exhaust manifold and through the turbo and down the exhaust.

So when cylinder 1 is on intake(will compress next), 4 is on ignition(will move to exhaust next), 3 is on exhaust(will move to intake next), and 2 is on compression(will ignite next) (hence 1423)

intake and ignition are on down strokes, and compression and exhaust are on upstrokes

Learns something new everyday on here. Cheers James, most enlightening






I guess it helps if you actually have an engine....:doh:....effing fleabay!