NEW(er) heads vs OLD heads

Wed Jan 18, 2012 4:25 pm

Saw something in a post today and it made me have to ask, what is the difference between the heads with the pop-up pistons vs the older flattop pistons... Is the heads different between the 2 ??? any pics would be great :D

Re: NEW(er) heads vs OLD heads

Wed Jan 18, 2012 4:31 pm

No pictures, but the heads with the "pop-up" pistons have a little metal taken out to allow clearance for the raised part of the piston, other wise it will hit in the edge of the chamber around the spark plug. May be other chnges, but that is the only one I know of. Doubt you could tell much by looking at a picture, it is a small change.

Re: NEW(er) heads vs OLD heads

Wed Jan 18, 2012 8:08 pm

The cylinder head changed in 1975, about 7 years after the pop-up pistons were introduced. One has nothing to do with the other. That said, it is always wise to check your engine at assembly to see if the piston hits the head. Heads get re-surfaced, blocks get decked, and castings vary a little. Some have had to do a little grinding- but I would say the majority are OK. If you have no problem with a head gasket, you are good to go. If you do, a little modeling clay will show you where you need to do a little work and if it comes to that, an old head gasket is handy to have. I have some comparison pictures but the later heads are very rare items on Cubs starting at ENGINE number 312390 including Numbered Series Lo-Boys.

Re: NEW(er) heads vs OLD heads

Wed Jan 18, 2012 8:30 pm

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Re: NEW(er) heads vs OLD heads

Wed Jan 18, 2012 8:57 pm

Bob, what's the top part # vs. the bottom?

Re: NEW(er) heads vs OLD heads

Wed Jan 18, 2012 9:02 pm

RaymondDurban wrote:Bob, what's the top part # vs. the bottom?


251 228 R1 and 355 691 R2

Re: NEW(er) heads vs OLD heads

Wed Jan 18, 2012 9:52 pm

TY SOooooo much, do you know if there is any difference in cc's of combustion chambers, as that would change what the static compression is....

Re: NEW(er) heads vs OLD heads

Wed Jan 18, 2012 9:56 pm

BullDAWG wrote:TY SOooooo much, do you know if there is any difference in cc's of combustion chambers, as that would change what the static compression is....

I have not cc'd them but I don't think they changed. I have some pipettes so maybe I can clean up a couple and check them.

Re: NEW(er) heads vs OLD heads

Wed Jan 18, 2012 9:56 pm

Are you saying that that PN head was only used from Eng SN 312390 starting in '75?
The 355 691 R2 head was being used on 154 Lowboys since I assume they rolled out in '68.
Dome top pistons were also being used since '68 in all model Cubs starting at Eng SN 264568.

From looking at the parts breakdowns, the F-Cubs switched to this same head sometime between '70 and '74, although I can't seem to find an exact SN. I don't see anything in the TC-37F that indicates anything changed with the head in '75.

Re: NEW(er) heads vs OLD heads

Wed Jan 18, 2012 10:00 pm

ok nube question but what is a "TC-37F" ????

Re: NEW(er) heads vs OLD heads

Wed Jan 18, 2012 10:02 pm

BullDAWG wrote:ok nube question but what is a "TC-37F" ????

Sorry, it's the parts manual. Here's a link: http://www.cleancomputes.com/Cub/Cub%20 ... index.html

Re: NEW(er) heads vs OLD heads

Wed Jan 18, 2012 10:05 pm

ENG-1 REV 20 has the serial number breakdown for Cubs and 154/185 Lo-Boys:
251 228 Rl
HEAD, CYLINDER
~ALL MACHINES EXCEPT CUB 154 AND
185 LO-80Y TRACTORSW/
ENGINE SERIAL NO. 312389
& BELOW
355 691 R2
HEAD,CYLINDER
-CUB 154 AND 185 LO~BOY TRACTORS-
-CUB TRACTORS W/ENGINE SERIAL
NO. 312390& ABOVE

Re: NEW(er) heads vs OLD heads

Wed Jan 18, 2012 10:12 pm

That contradicts the Eng-1 Rev2 that has the PN for the 154 head as being 355 691R2 as early as at least Sep 1970.
http://www.cleancomputes.com/Cub/Cub%20 ... age-15.jpg

Re: NEW(er) heads vs OLD heads

Wed Jan 18, 2012 10:19 pm

RaymondDurban wrote:That contradicts the Eng-1 Rev2 that has the PN for the 154 head as being 355 691R2 as early as at least Sep 1970.
http://www.cleancomputes.com/Cub/Cub%20 ... age-15.jpg


Depends upon how you read it. Looks to me like all Cubs below that number have the old head. All tractors above that number have the new one.

Re: NEW(er) heads vs OLD heads

Wed Jan 18, 2012 10:28 pm

bob in CT wrote:Depends upon how you read it. Looks to me like all Cubs below that number have the old head. All tractors above that number have the new one.

That page I linked was from 1970, five years before Eng SN 312390 was made.