B7100 Piston Installation

[Schmotown]

Duck Wrangler, first I used a dial indicator at the center of the piston. I then used your "arbitrary" method to confirm TDC with a degree wheel Thats the way I always found TDC. Both methods provided the exact same results.

Wolfman, I did use .008 valve clearance. Just rechecked top of piston to bottom of head with solder.
Specs are .0237 to .0315. My readings 1) .037, 2) .038; 3) .038. I haven't found any data on volume for these heads. Don't know if milling approx. .008 would make any difference. I'm not an engine guy.

Thank you both for your advice. I'm gonna go look for a weedy area and roll this junker into them as a historical artifact!!

 

[Hugo Habicht]

Hi Larry,

I only read your first post in this thread, so I may have missed it, so please forgive me if I am repeating something you did already.

Did you grind in the valves with the new head?

Kind regards,

 

[Schmotown]

Hi Larry,

I only read your first post in this thread, so I may have missed it, so please forgive me if I am repeating something you did already.

Did you grind in the valves with the new head?

Kind regards,

Yes, I lapped the valves, Thanks for your input.

 

[North Idaho Wolfman]

Did you go to a dealer and get the head gasket, or was it online order?

 

[Schmotown]

Did you go to a dealer and get the head gasket, or was it online order?

I bought the gasket from Messick's. Best of my knowledge it is a genuine Kubota gasket. I've decided to go back to square one and review everything I've done to the engine. If I don't find anything I'll remove the front cover and confirm that the timing gears all line up. I'll keep you posted.

 

[North Idaho Wolfman]

Things that affect the volumetric numbers and compression numbers:

Doubling the injector compression gaskets (copper /clad sealing rings).
Wrong glow plugs:
Wrong valve fitment ( Did you buy the head complete or did you install your own old valves?)
Precambers left out.
Wrong or too think of head gasket
Installing metal head gasket shim when not needed.
Installing wrong pistons
Installing rings upside
Wrong head
Bent connecting rods

 

[Schmotown]

Things that affect the volumetric numbers and compression numbers:

Wolfman, my replies are in "red". Thanks for your thoughtful post.

Doubling the injector compression gaskets (copper /clad sealing rings).
There is one copper washer on each injector.
Wrong glow plugs:
Not sure but there are NGK Y103K glow plugs installed. I am having a bit of trouble cross referencing that number.
Wrong valve fitment ( Did you buy the head complete or did you install your own old valves?)
I bought the head complete from Kumar Bros (KB).
Precambers left out.
I don't think KB heads are made the same way as Kubota heads, I think their prechambers are cast into the heads and aren't removeable.
Wrong or too think of head gasket
I installed a Kubota head gasket. I have one that I originally used and when I pulled the head the 2nd time I kept that gasket. It measures .050 after being torqued. Manual specs .0413 to .0453.
Installing metal head gasket shim when not needed.
No shim installed.
Installing wrong pistons.
New Kubota pistons, rings, bearings. Verified part numbers.
Installing rings upside.
I'm 99% sure the rings are installed correctly.
Wrong head.
Not sure, that will take further research on my part. I foolishly sent my original head to the junk yard.
Bent connecting rods.
Not sure but the stick out above the block is per specs so I think they're okay.

I just redid my leak down test on all cylinders. 5% to 6% leakage range. If I have that tight of a rebuild on the engine then my low compression numbers must be due to a volumetric issue. But I have one consideration that may throw my logic off:

My leak down numbers were achieved with both valves closed and the piston on TDC of the compression stroke on a non-rotating engine. If the gear timing on the front of the engine is incorrect could that result in a low compression reading when cranking the engine? Could something mechanical be taking place that I'm not understanding?

Sorry for asking all the questions but I do appreciate everyone's experience.