Returning My G3C to 350cc

[RichardS]

Russell, apologies for the name mix up!

Clearly the unflanged barrels I have are indeed AlFin types as they do have those patent numbers, but no branding.

Live & learn.....

Good job I never needed to try to press a liner out !



I have now found the Abstracts for 599752 and 606330. Unsurprisingly, they both relate primarily to manufacturing aero-engine cylinders during WW2.
https://www.patentguru.com/GB599725A

https://patents.google.com/patent/GB606 ... =uk+606330

Essentially it appears to be a process of 'tinning' the liner surface (like tinning a soldered joint) before then casting the alloy around the liner. 606330 also includes an intermediate stage to heat treat the (steel) liner to harden it.

US Patent US2396730 filed in 1941 looks to be the source of the art
https://patents.google.com/patent/US239 ... =US2396730

Amusingly they later lodged closely related patents for making aluminium bonded stainless steel kitchen utensils, very "guns to plough shares"

An interesting digression...........

[Joker_Bones]

I feel fully enlightened on the Al-Fin process, that was a pretty comprehensive description in the patent abstracts.
From the article earlier "This bonding process was a closely guarded operation"... Not exactly a secret if you read the patent

[jimh]

Just a thought on reading this thread, with the Cylinder head 'seal' being the lapped in joint in the head between the barrel liner and the head itself the Al-fin process must have been able to withstand the constant downward pressure when the head is tightened down and the liner not 'slipping' down particularly when the engine is up to running temp, or am I thinking this wrong!

[mdt-son]

Good cylinder liners are made of ductile iron. The material is very wear resistant and has elongation properties making it better suited to alloy barrels than spun cast grey iron.

https://powerbore.com/ductile-iron/

- Knut

[Joker_Bones]

This long stroke Al-Fin barrel is spigoted, the recess in the head is clear of the spigot... So lapping the head and barrel together does not cause pressure on the liner alone when the head is tightened down.

IMG_20230614_162220.jpg

[mdt-son]

J-B, if the cylinder bore is worth keeping and spigot looks good, you may lower top deck of the barrel outside if the spigot by turnng, thereby allowing spigot and the head's recess to meet up. Ensure that spigot and recess are flat and even.

- Knut

[jimh]

J-B,Knut, are you saying if the recess in the head for the barrel spigot is lost due to years of 'lapping in' the only solution is to get a light skim off the top of the barrel liner?

[mdt-son]

jimh, I was considering the "normal" scenario as described in the service manual. As you pointed out above, the primary seal are the lands outside the spigot and the corresponding recess in the cylinder head. Now, looking at your scenario of a well used barrel and cylinder head. If by too much grinding of the lands, the annular space between spigot and recess is lost (see extract below), the spigot will bottom in the recess, and the primary gas seal (the lands outside the spigot/recess) will not be in contact, i.e., they do not form a gas-tight seal. It can be restored only by either shortening the spigot by skimming, or (probably the better way) by machining the recess to increase its depth. It's essential all faces at the joint are parallel and square to the bore axis.

Here is an extract from the factory service manual, describing the "normal" scenario for a new C/CS/TCS engine, to be run less cylinder head gasket.

"Cylinder head and barrel joint. Normally there is an annular space between the spigot on the
cylinder barrel and the small face on the cylinder (head), when the cylinder head is assembled. This space
can be eliminated by individual machining, assuming the necessary machining facilities are
available. To do this, machine back the wide face on the cylinder head, leaving a gap of .001"
between the small recess in the cylinder head and the narrow spigot on the cylinder barrel. Use
grinding paste on the wide face of the cylinder head, also in the small recess. Grind the head on
to the cylinder barrel until both faces on the cylinder head are mated to the cylinder barrel to
give a gas- tight joint. Should an oil leak develop from the cylinder head
face, regrind the spigot (in) situ only."

- Knut

[mdt-son]

This long stroke Al-Fin barrel is spigoted, the recess in the head is clear of the spigot... So lapping the head and barrel together does not cause pressure on the liner alone when the head is tightened down.

J_B, do you intend putting this set into service? If the concentric circles are scores in the metal, I would consider having lands at the cylinder barrel and cylinder head machined if I were you. Consequentially, spigot and recess may have to be machined also.

- Knut

[Joker_Bones]

Knut... That's the pattern left in grinding paste when they were separated.

IMG_20230727_165441.jpg

No grooves when wiped off