Visual differnces between a 3/1 and 5/1

[Zagato]

I am interested in a CS which is 350 miles away.  The seller has sent me phone pictures of the brass plate.  Although not clear it does look like a 3 not 5 for the HP rating.  Are there any features on the outside of the machine that would differentiate a 5/1 from a 3/1 - thanks

Perhaps I could tell what model it is by the speed rating or RPM rating on the brass plaque...............are they different

[contaucreek]

3's and 5's are 600 rpm, 3.5's and 6's are 650 rpm.

[compig]

Chris,
As far as I know there is no visual difference between a 3/1 and 5/1. The only difference is the bore diameter. Also, there was a 3-1/2/1 !! But speed is 600 for a 3/1 and 650 for the 3-1/2/1.

[Zagato]

Thats not good news if their is nothing on the plate to distinguish either model.  Sadly, looking at the picture I don't think there is any doubt it is a 3 not a 5 but will investigate further.

Did you get my pm re the SOM and apologies about the phone cutting out last night.

[compig]

Yes Chris, no problem. Is there any other info on the plate, a spec number perhaps ?

[Zagato]

Perhaps it says Spec not Speed, the photo cuts it off.  I have already asked for the other figures so hopefully I can get this resolved.  Will let you know outcome ASAP hopefully.

[Zagato]

Well we are not getting very far.  RPM little help as they are both the same @ 600.  Cannot get a closer picture downloaded!  What is the spec number?  Would that tell me what model it is.........I am losing this one, a 700 mile round trip trip is too far to discover it is a  3/1  I have heard it runnig over the phone and it does sound very nice, no nasty knocks, even beat etc but a no no if it is a 3/1.     

[compig]

Chris,
Have done a bit more investigation, the 3/1 has a unique head. If you ask the seller to remove the rocker cover and take a pic looking directly down on the head I could identify if it's a 3/1 or 5/1.
Out of interest the fuel pump and injector are also different for the 3/1.

[Zagato]

Thanks Gary, I think the seller has had enough for a while which is understandeable.  I don't think I could push him to take the rocker cover off.  I am off to the Grand Prix tomorrow so will try calling him one more time tonight.  Thanks for doing the extra digging.

Chris

[compig]

Grand Prix !!! Lucky man, should be a cracker !! 

[M61hops]

Hi Zagato, I'm no expert but I think that a 3-1 has a 1 1/2" diameter crankshaft and 5-1's and later had a 2" diameter crankshaft  .  You might be able to see that difference in a photo or the seller could measure for you.  Hope that helps!                        Leland

[compig]

No, 3/1 and 5/1 cranks are the same. Good try though !

[Zagato]

This is the problem, you can see how one extra mark can confuse a 3 with a 5.  Can anyone look at their 3/1 and tell me if their 3 looks looks like the first or second 3.  If it's a 3 like the first one e.g. like this  3  then I am safe but if it like the second one in the picture then you can see how the confusion can arise.

 

Thanks for the reply M61hops.

Chris

[compig]

I have an plate from a SOM in front of me and the 3's look like the second in you image.

If you seller would oblige with that photo it will categorically ID the engine as a 3/1 or 5/1.

[Zagato]

Oh dear keep coming up against dead ends    The only thing left is the SPEC number.  The one on Ebay starts with 5/1 if only someone with a 3/1 could tell me if their spec number starts with a 3/1 that would resolve all this.

I don't suppose your 6/1 has the old brass palte and starts with 6/1 on a spec number...