For the love of a tractor engine: The life and times of the 18R-G

[Norbie]

I'm feeling the love, Witzl style!

[Steve M]

The 18R and 18R-G vacuum advance mechanisms are different in vacuum resolution and also fitting depending on which model 18Rg dizzy you have.

We have an 88230 dizzy here that uses a vacuum advance that has too small a diameter where it mounts into the dizzy casing for later model one to fit. You'd have to modify either the housing or the vacuum advance. (the casing on this one uses an RT-40 dizzy cap and the casting is similar to that model dizzy in other respects and also internally.

Later models (88251, 88270) use a more regular sized advance unit (the models that are suited to the 22R electronic conversion).

The 88230 one that we have acts from 0mm/hg upwards with the action levelling off at about 150mm/hg.
The 18R one starts acting at about 150mm/hg and levels off at about 330mm/hg.

I do original 88251 and 88270 ones that I could measure up to see where they work. I would have to find them though, which is not such an easy task these days, we put everything into boxes and stacked them...bad move.

Hopfully this helps, but if you really want the specs of the later model ones. let me know and I'll tack it down for you.

[Norbie]

Thanks for the info!

I'm not 100% sure which dizzy I have, I just bought the engine and don't know its history. Perhaps o_man_ra23 would care to enlighten us?

[Steve M]

If you post the part number of the diaphragm I could check what I've got and how it compares to other types.

[Steve M]

Norbie, still on the topic of the vacuum advance, here's a link to where I just put up the specs from the 1977 edition of the 18R series engine repair manual.
It pretty much backs up what I said first time, only it states what the figure i measured were supposeed to be.

http://www.toymods.net/forums/showthread.php?t=4080

[scootaphill]

has any one ever cc the combustion chamber of the head while its been apart? id be curious to see where its at

cheers

[YelloRolla]

If I remember correctly it is 70cc. Witzl will confirm, his brain is younger than mine (prolly sharper too).

[The Witzl]

yep, 70cc or 71cc

you've got my green book with that written in it IIRC jason

[scootaphill]

what model head was that? did you happen to cc the block as well?? and if so what pistons were used?

thanks, now i have something to compare to when the time comes!!
phill

[The Witzl]

that's a stock 88250 head which had just been rebuild.

[Damo82]

Guys, does anyone happen to have a photo of the exhaust side of an 18RG and 18RC head?

I am heading out to check a set of extractors that "may" be for an 18RG and I was just looking for some reference material. Unless anyone knows an obvious way of determining the difference between 18RC and 18RG extractors.

I know 18RC has the inlet manifold above the exhaust manifold but that isn't going to help that much.

Cheers

Damo

[Norbie]

Port spacing is pretty different so you shouldn't have a problem telling them apart.

18R-G:  O       O       O       O

18R-C:  O          O O          O

[Damo82]

Thanks Norbie, you are a god. +rep for you

Damo

[Steve M]

If I remember correctly it is 70cc. Witzl will confirm, his brain is younger than mine (prolly sharper too).

When we measured the 88251 and 88270 heads, they both came out to an average of 72ml on the dot.
Maybe that's one more way that they dropped the compression on the later models.

[scootaphill]

great work karl and steve... you guys didnt happen to cc the blocks as well

when my motor is apart i'll be sure to cc my block with the 22r/e pistons as a comparison

cheers