guys i bought a old servi and trying to see whats what? first the frame and rear end is 1932. cool but the motor bottom is 41 wld as the tranny but not sure on the top end. iron heads and can't make out all the numbers on the jugs? 120-3? i know what they should be but can any one tell me what the are on a g or wl? this narrows it down for me. thanks

 

There are 3 different iron heads used that also came in 3 different compression ratios. The 1937 to 50 have 3/8 stud holes high 4.5 medium 5.5 and low 6.8. 2nd version 1951 to 52 WL and 51 to 55 Servi cars have 7/16 bolt holes and only available in medium compression marked 5.5. The 3rd version 56 to 73 have 14 mm spark plugs holes instead of 18 for earlier and have 7/16 bolt holes and larger fins. marked 5.5 for medium compression.

 

Thanks for your help

 

Hello-

Perhaps you meant 4.5 cr as low (not high) my '73 Servi HAD 4 3/4:1 Cr stock.

And High is 6:1 cr, I know, cause that's what I added on my 45, after I stroked it..

 

I'm looking at my 1940 parts book it reports heads marked 6.8 as low compression heads for 1929 to 1935 45". And 36 to 40 45" were also offered in 6.8 Low compression heads. Heads marked 4.5 are used on the DLD, RLD, and WLD models. Heads marked 5.5 were for High compression models for 1929 to 1935 and 1936 to 1940. The book only goes to 40 so they may have been used later than that, I will have to dig out other parts books to be sure.

 

this is the note i got from 45 performance.4.5 with tree fins on the bottom is high compression and 2 fin 6.0 is low compression. the number is the size of your combustion chamber of the head " smaller = higher compression. these are iron heads

 

thanks for the help on the wld heads. if you know of any thing else special about the wld motors mine is a 41 id like to hear about it. as far as i know the only thing different was the heads were high 4.5 and the intake and maybe the carb were bigger. i still have not found out what the "d' stands for in wld. as far as i know these were 45 two wheel solo models high compression

 

WLD was the sports model with high comp heads and better cams.
The '41 had alloy #6 heads as standard.
I've never seen an explaination of why the used the letter D.
When first introduced they wouldn't have known they'd use A for army and no way of knowing they'd need C for Canadian.
This begs the question,what happened to B?

 

Thats the first i've heard of better cams. I always thought they where the same as wl. they went with a better flow, extra high compression heads, better flowing cylinders and intake an carb. can't find out any more on them

 

The cast iron heads are marked on the underside in cubic inches, so a larger number will indicate a lower compression ratio. They would measure the combustion chamber sizes so that they could match up similar heads on the same motor on the assembly line.

The aluminum heads are marked on the edge on the right side, and they are stamped with the compression ratio, so a larger number indicates a higher compression ratio. You should always make sure and match compression ratios or the bike will never tune correctly.

The cast iron heads have a -36 part number, used on engines from '37-'39 and optional for '40-'41 solo models. There were also some -51 heads that had a larger diameter stud hole to accomodate the new head bolts, and a -55 head design that was for servicars issued to police departments (5.5:1 compression and a 14mm spark plug hole instead of the 18 mm hole in all other models).

The aluminum heads have a -39 part number, first used on the '39 WLDD and '40 and later WLD and WLDR, all military WLA and WLC, '46 and later solo models.

My notes indicate that the best street compression ratio available at the time was 5:1, although a racing model (WR) featured 6.25:1 ratio.

If you plan on breaking down the motor, check to see if you've got the copper head gaskets (-36 part number) and not the asbestos (Steelbestos, Corbestos) gaskets (-39 part number) which were designed for the aluminum heads but will work on cast iron heads. If you have the asbestos gaskets, disassemble the motor while pouring on water (or some other liquid) so that the asbestos dust doesn't break free into the air. Asbestos is bad stuff and it doesn't take much to mess you up.

I would expect the cylinders to be a -36 part number, since that was used from '36-'50 with cast iron heads. The -40 and -40M part numbers were used with aluminum heads, and does not have studs in the cylinders as these were replaced with bolts. The -40 cylinders will also work with the -51 cast iron heads (servicar), and the whole package (cylinders and aluminum heads) will retro back to the '36 cases if you're not worried about being correct. The -40M (military) cylinders require a .095" spacer under the head bolts or they will bottom out (don't ask me why the head bolt holes were 31/32" deep instead of the normal 1 1/16" deep).

You can tell the -40 cylinders from the -40M cylinders because the M's have an irregular fin profile in one spot (where the fins don't seem to meet up smoothly), and the regular -40 cylinders have a smooth fin profile. Like I said earlier, you've probably got the -36 cylinders which also have the irregular fin profile in one spot.