fire ring

[ridgerider]

continuing my knuck education...do both 61" and 74" cylinders and heads have a fire ring?

[Ultrashovel]

continuing my knuck education...do both 61" and 74" cylinders and heads have a fire ring?

I may have got this wrong, but as I recall, the only difference was the bore.....3-1/2 versus 3-7/16". I seem to recall a chrome top ring but it's been a long, long time.

[ridgerider]

did'nt mean to ask the impossible ? trying to figure out what all i have, was told that the 74" cylinders were taller and thus had no fire ring,  but my heads do have a fire ring,,,looking for a postive way to tell the differnce between 61" and 74" other than bore..


thanks

[Ultrashovel]

did'nt mean to ask the impossible ? trying to figure out what all i have, was told that the 74" cylinders were taller and thus had no fire ring,  but my heads do have a fire ring,,,looking for a postive way to tell the differnce between 61" and 74" other than bore..


thanks

IIRC, if we are talking about a Knucklehead, the 61" cylinders were noticeably smaller. They also had fewer fins below the area where the manifold nuts connected to the cylinder heads. This made it possible when viewing an engine from the left to easily determiine whether it was an EL or an FL. I don't know whether the cylinders were shorter or longer, but I do recall that both of them had three ring pistons.

If you are asking whether the 61" might have had only two rings (no top or "fire" ring) then I can say definitely that they did have three rings on both engine sizes.

Other differences were the stroke on the 61  which was 3-1/2" versus the 74 which was 3-31/32". I always wondered why they didn't make it an even 4", but I digress.

The 61 crankpin had the same size center area as the 74 where the rollers run but the tapers were smaller. I recall that I stroked my 1950 FL and I used 80" UL flywheels with the UL pin, which was the same as a 61" pin. This gave a 1/4" stroke increase so I made some clyinder plates to raise the barrels 1/8" to match. The pistons hit the flywheels on the bottom so it was necessary to cut the bottoms down.

Also, the UL flywheels were smaller in diameter so they wouldn't come close enough to the breather pocket. I had to add some sheet brass scrapers held in with screws to get the oil off of the flywheels It all worked. LOL.

[ridgerider]

i was asking about top of the cylinder that has a raised portion  that fits in a groove in the head, if both 61 and 74 were the same in that aspect, kinda like a shovel cylinder..

[Ultrashovel]

i was asking about top of the cylinder that has a raised portion  that fits in a groove in the head, if both 61 and 74 were the same in that aspect, kinda like a shovel cylinder..

Someone may correct me since it's been many years but I would say that they were similar in that respect. That's usually called the "spigot".

[Speeding Big Twin]

ACCORDING to page 160 of Palmer: ‘There is only one type of the 1941â€"1947 74 cylinders: the 1941â€"1947 “five-fin” cylinders. This cylinder is made from the same casting as the 1940â€"1947 61 “five-fin” cylinder ... In addition to the larger bore size, it is quickly noticeable when off the motor by its lack of an upper lip at the edge of the bore which the 61 cylinders and all 1948â€"1965 cylinders have.’

However, some of us know there are plenty of errors in Palmer's book so I CANNOT say if his info regarding the upper lip is correct. Can anyone confirm what Palmer says? And if so, please state how you know his info is true, if indeed it is.     Eric

[ricochet]

I know for certain that there is a difference in length between gasket surfaces but do not have the dimentions handy.  Somewhere about .200 difference.

I just found this     http://knuckleheadtheology.blogspot.com/2007/03/great-knucklehead-cylinder-controversy.html                Has a good deal of info from various sources.  Accuracy is not assured at least by me.  Good read nontheless.

ricochet

[ridgerider]

this is helping, if my cylinders are 61" with a spigot lip and bored 20 over 74" and shorter than 74" cylinders ??my compression must of been way to high, ricochet do your mike brown cylinders have a spighot lip on top? are your heads groved to accept it?   i thought there were more of us with knucks... thanks

[ricochet]

My MB cylinders do not have the firering and do bolt up directly to the heads if the stock knucklehead bolt pattern was kept on the heads.  Remember many are switched over to pan cylinders. 

If you want vast amounts of knowledge and great reading go over to  flathead power    http://www.sscycle.com/tech/

It looks a bit different in there since S & S took over but the forum is a wealth of knowledge.

ricochet