Top clearance and iming issues

[Kubota-KLS]

I recently rebuilt a D902 engine in a RTV900X. When I started it, the engine sounds excessively loud, possibly pre-detonation. I checked the injector pump for timing. When i went to line the timing mark on the flywheel, the timing marks lined up with #2 cylinder not #1. When I installed the flywheel, I noticed that the holes were not symmetrical. I turned the flywheel until the holes lined up with the crankshaft holes. Another issue I am having is top clearance. The WSM stated the specs are .0197 to .0276. Two of my cylinders are .20 the third is .013. I don't understand how it could be that far off. The machine shop that worked on the block for me ordered the pistons from an after market supplier. Does anyone know how to remedy my issues?

Thanks for your help and advice,

Kevin

 

[GeoHorn]

I’m no expert on this…. but I seem to recall there’s a “shim” type of headgasket which addresses this sort of thing….

 

[North Idaho Wolfman]

Timing is affected by shims under the pump, and the gears on the front of the engine.

There are 2 different pistons for that engine depending on serial number.

And one other thing that could affect it is if the piston was installed backwards, they are directional.

 

[Henro]

Timing is affected by shims under the pump, and the gears on the front of the engine.

There are 2 different pistons for that engine depending on serial number.

And one other thing that could affect it is if the piston was installed backwards, they are directional.

Curiosity question:

Assuming the difference is due to pistons being directional and needing to be installed correctly. How would one determine whether two of them are reversed, or one of them is reversed? I mean, if the difference was due to installing piston(s) the wrong way…

It would seem that even if the wrong pistons were installed, when the measurement was taken, if they were installed properly, they would all measure the same.

Again, just call me curious…

 

[lynnmor]

Pistons often have a slightly offset wrist pin to help prevent piston slap. The height should be the same even if they were installed wrong.

 

[North Idaho Wolfman]

Pistons often have a slightly offset wrist pin to help prevent piston slap. The height should be the same even if they were installed wrong.

The is an indent in the piston, if the pistons were installed wrong then the indent would change the clearance.

 

[fried1765]

Timing is affected by shims under the pump, and the gears on the front of the engine.

There are 2 different pistons for that engine depending on serial number.

And one other thing that could affect it is if the piston was installed backwards, they are directional.

Issues such as this, are why IMHO, it is often best to buy a short block, if/when available.

 

[North Idaho Wolfman]

Curiosity question:

Assuming the difference is due to pistons being directional and needing to be installed correctly. How would one determine whether two of them are reversed, or one of them is reversed? I mean, if the difference was due to installing piston(s) the wrong way…

It would seem that even if the wrong pistons were installed, when the measurement was taken, if they were installed properly, they would all measure the same.

Again, just call me curious…

Pistons are marked for direction.
yes they should all measure the same.

 

[Henro]

Pistons are marked for direction.
yes they should all measure the same.

I kind of realize that… But my question was first, what if all the pistons were wrong how would we determine that?

Second, if the Pistons were right (or wrong), and one or two of them were reversed, how would we determine that? I mean, how would we determine which one was wrong?

Inquiring mind wants to know… and no, I never read the National Enquirer tabloid…LOL

edit: So the OP has two of the three pistons within spec. Does this is mean that chances are pretty good he has the right pistons at least in two positions? Not sure why I got interested in this since it’s never gonna be an issue for me… But I really am curious. If the wrong pistons were installed, is there a chance they would be in spec? And the questions go on…

 

[North Idaho Wolfman]

I kind of realize that… But my question was first, what if all the pistons were wrong how would we determine that?

Second, if the Pistons were right (or wrong), and one or two of them were reversed, how would we determine that? I mean, how would we determine which one was wrong?

Inquiring mind wants to know… and no, I never read the National Enquirer tabloid…LOL

edit: So the OP has two of the three pistons within spec. Does this is mean that chances are pretty good he has the right pistons at least in two positions? Not sure why I got interested in this since it’s never gonna be an issue for me… But I really am curious. If the wrong pistons were installed, is there a chance they would be in spec? And the questions go on…

Here is another scenario the pistons are fine and the rods are damaged.
2 of them can be compressed and that is causing the mismatch.

When I build engines I match all components before install, it cuts out issues.

One other option is testing error, I've personally tested component's and they look bad on initial test then retest showed them good.

I'm thinking there might be some testing error as he says that the timing marks do not line up, that can't happen and actually have it run.

 

[Kubota-KLS]

Would Like to thank everyone for your input. I think I will remove the engine. Then I can recheck to see it the flywheel installation correctly. I will also remove the head and conduct a top clearance test that is in the WSM. it will be a more conclusive test as to my actual top clearance. I would like to say I am 100% sure the pistons are in the correct way but I will soon find out. Thanks again. Kevin

 

[Kubota-KLS]

Here is an update since my last posting. I removed the engine to check it for injection pump timing, top clearance, and flywheel installation.

The cam timing gear, fuel injection pump gear, and idle gear lined up correctly.

The top clearance (distance from the top of the piston to the bottom of the head) was less then the service manual specs on one of the pistons (.013). I spoke to the service manger of the local Kubota dealer. The told me it was more likely that the problem was the aftermarket pistons. He said that it would increase the compression in that cylinder which he did not think it would be problem to running like that.

The flywheel was on the crankshaft correctly. i have no idea why, but for some reason the timing marks on the flywheel do not line up with #1 cylinder in TDC, but #2 cylinder. I just have to use #2 cylinder to check injection pump timing.

Since I did not have any shims to just the injection pump timing, I bought a few shims as a starting point to adjust the injection timing. With the engine removed from the RTV and the head removed, i was able to check the injection timing easier. it looks like the injection pump was 26 degrees without shims. With the shims i bought i was about to set the injection pump timing to 18 degrees which is within specs.

When i got the engine back in the RTV, it started and ran great. So I believe the bottom line is to make sure the injection timing is set properly.

I would like to thank everyone for their input.

Kevin