67mm Pistons ??

[dirtdigger]

The earlier cylinders didnt use the extra seals. Honda used the extra dowels and seals to try to stop the head gaskets from seeping oil because the stock cylinder studs stretch over time causing the head gasket to seep oil. If you look in between cylinders 1and 2 and 3 and 4 it is welded up if done properly. The 72mm cylinders are so big they break through the air gap when machined that large. If not welded up it will leak oil. Guys that do it the cheap way fill the gap with silicone instead of welding it. any questions about big bore motors feel free to ask

 

[grewth]

The earlier cylinders didnt use the extra seals. Honda used the extra dowels and seals to try to stop the head gaskets from seeping oil because the stock cylinder studs stretch over time causing the head gasket to seep oil. If you look in between cylinders 1and 2 and 3 and 4 it is welded up if done properly. The 72mm cylinders are so big they break through the air gap when machined that large. If not welded up it will leak oil. Guys that do it the cheap way fill the gap with silicone instead of welding it. any questions about big bore motors feel free to ask

That was the next question I was about to ask, because, yes, there's silicone sealant between the cylinders.
Oh well, too late to weld them now, it should have been done before boring out for the liners.

 

[Loki]

Looking at the photos I'd say there would be very little meat left if the counterbores were present, perhaps a smaller counterbore with thinner O rings might work?

Loki

 

[dirtdigger]

They are un necessary. Honda only used them because the earlier engines would seep oil after the cylinder studs relaxed and let the head gasket seep oil eventually. If you use heavy duty studs with a good headgasket you wont have leaks. I dont use the late cylinders and never have issues with oil leaks.

 

[grewth]

It does make you wonder why Honda didn't just uprate the studs in the first place, rather than introducing seals that would mask the issue instead.

 

[dirtdigger]

A lot of things engineers do make you wonder. Adding another seal isnt the worst thing in the world. I am sure it all comes down to what is more cost effective. Probably had thousands of studs already made and it was easier just to machine for the seals and add some more seals then it would be to re engineer the studs and use more material, then you have a bunch of supply of the old studs you dont use anymore. One of those things we will probably never know the exact answer for.

 

[Old_Crow]

A lot of things engineers do make you wonder. Adding another seal isnt the worst thing in the world. I am sure it all comes down to what is more cost effective. Probably had thousands of studs already made and it was easier just to machine for the seals and add some more seals then it would be to re engineer the studs and use more material, then you have a bunch of supply of the old studs you dont use anymore. One of those things we will probably never know the exact answer for.

My father was a mechanical engineer and I spent 35 years as an auto mechanic. We used to have conversations about the strange choices engineers sometimes make. It was his position that a lot of those strange choices were driven by the bean counters rather than legitimate engineering choices.

 

[dirtdigger]

I agree with that. As an automotive and heavy equipment mechanic you work on stuff that makes you frustrated and scratching your head because of how things are designed and made because you can obviously see easier ways to do things.