B7100 Head Gasket

[WilGan]

New Member, I acquired a B7100HST D that I'm pretty sure the head gasket had a leak or the head was cracked. I had white smoke constantly and I couldn't keep it from overheating after 5 to 10 minutes of running. I removed the cylinder head and the head gasket laminated in shreds, some sticking to the head some sticking to the top of the crankcase. I couldn't tell where any leaks may have been happening. I cleaned the head and clamped a plate with a gasket on the bottom (Cylinder side) of the head, I then filled the head with water and let it set for a few days with no apparent leaks, I then machined a plate for over the discharge area and fit an air hose on it to pressure test it, I did get some leaks but, they seemed to be coming from my gasket setup, I had no visible water in the intake or exhaust areas. Concluding I believe that the head is not cracked.
Looking for some confirmation that I have checked this well enough to rebuild.
When I went to clean the head gasket from the top of the crankcase, I noticed a small soft rubber flat ring gasket around the pin pipe (Ref No. 110) that sticks up from the cylinder housing. I'm thinking the was the o-ring Ref No 140 Part Nu 15221-33700. not sure.
Any advice would be appreciated. Thanks

 

[Selkirk_D]

One thing I have seen in other engines is a crack around a guide or under valve seat that only leaks when engine is hot. Barring that, I’d check block and head for flatness and if good, and head leak check is confirmed good, I’d put it back together and see. Did you happen to run a compression test before you tore it down? Low on two adjacent cylinders is a definite blown head gasket.

 

[North Idaho Wolfman]

Take a good picture of the head showing the valves and prechamber.
3 pictures.
I can spot the leaks every time.

Get An OEM head gasket, NO aftermarket head gasket!


Head gasket: 15371-03312
O-ring: 15221-33700 (some Head gasket sets come with the O-ring)

 

[D2Cat]

Be sure to get the O-ring, and situated correctly. That is an oil passage.

 

[WilGan]

Be sure to get the O-ring, and situated correctly. That is an oil passage.

Thank you I will make sure, I suspected that's what it was

 

[WilGan]

One thing I have seen in other engines is a crack around a guide or under valve seat that only leaks when engine is hot. Barring that, I’d check block and head for flatness and if good, and head leak check is confirmed good, I’d put it back together and see. Did you happen to run a compression test before you tore it down? Low on two adjacent cylinders is a definite blown head gasket.

Unfortunately, I did not do a compression check. Hindsight I guess I should have. I just jumped right in and took it apart. I imagine I could check it after I re-install the head and torque it, right? if it is cracked around the guides would the compression check verify it that it is or isn't cracked? I know the gasket would be out of the equation then. I will check the flatness on Monday, I want to inspect it on a surface plate and run an indicator under it. Does a warped head indicate a crack or just the source of a head gasket leak. Flatness should be less than .002 correct?

 

[WilGan]

Take a good picture of the head showing the valves and prechamber.
3 pictures.
I can spot the leaks every time.

Get An OEM head gasket, NO aftermarket head gasket!


Head gasket: 15371-03312
O-ring: 15221-33700 (some Head gasket sets come with the O-ring)

 

[North Idaho Wolfman]

The right is the only one I Question?
If it is a crack that is not typically how they crack.
Take some brake parts cleaner and get the oil / antifreeze off of it then take another pic if you would.

If you pull those two valves out, if it is cracked you'll see it in the seats of the valves too.

 

[D2Cat]

You might be able to take the head to a machine shop and have them magnaflux it foe another opinion.