I bought this engine here in the classified section. It is suppose to be a 41 cc engine. I don't see any markings on it, besides a serial number, and a U.S. Engines tag. I know they make other engines close to this size. How can I be sure of the CC's?.

The label with the serial number on it has the model number of the engine. The first two digits of the model number are the displacment figures.

The Model number is 257951. So is that 25 cc's or 2.5"
Thanks for the help.

hmmm i think my g38 is a 2.3 so 2.5" sounds right for a 41cc.

2.5"=41cc, that is right. The question is if the 25 on the serial # means cc's or in". The 25cc engine is very close in size and weight to the 41cc. I'm fairly sure I have the 41cc. The serial number sticker is also on very loose, just want to be sure.

here is a pic of the 25. A lot of metal on the front.

I don't have that extra metal in front of the cylinder. I must have the 41cc. Thanks

The exhaust is on the back of the cylinder on the 41 too. I have had both, still have two 41's
I love them both!

rameleni,

If it's a 25cc it'll have side exhaust. If it's a 41cc it'll have rear exhaust.

The US 25cc is based on the Homelite weedwhacker engines. The US 41s are based on the old Quadra 35-40s.

Jim

That model number would indicate a 25 cc engine. The 41 cc would have a model number of "41XXXX".

The 25 also has a bolt on cylinder. the 41 cyl. is part of the upper crankcase. The plug is also slanted back on the 41.

If I may chime in, I have had both the 41cc and the 25cc engines, the photo in post #6 is a the 25cc.

I still am not sure which engine this is. I just put a picture of it in my gallery. I measured the exhaust port. It is 1"x 1/2" square. I called hobby services, and gave them the model number. They also said it is a 25cc. everyone who see's a picture of it, says its not a 25cc.

rameleni,
That is definitely not a 25cc. It's a 41.

Jim

That motor is either a US 35 or US 41, but it is definitely not a US 25.

OK, I'm thoroughly confused.

rameleni1 asked which displacement US Engines he had.

Bill Baxter, Manager of the Futaba Service Center USA for Hobby Services, and who is also one of the moderators for the US Engines Support link under the Engines Forum, stated, "The label with the serial number on it has the model number of the engine. The first two digits of the model number are the displacment figures."

rameleni1 then stated, "The Model number is 257951", to which Bill Baxter then stated, "That model number would indicate a 25 cc engine. The 41 cc would have a model number of "41XXXX".

Yet others are still saying it's a US 41. It LOOKS like my 41cc and I always understood the 35cc and 41cc looked identical and the 25cc (which I understand has been discontinued for some time) looks completely different.

So which is it - a 25 or a 41?

And here's another wrench to throw into this. I just went and checked MY US 41 and the serial number on the tag affixed to the engine says 006956. So what do I have - a"00cc" engine???

The one thing I can say, is that the seller of the engine to me has been very cooperative. I have triple checked the model number, and called about it. Same outcome every time, 25cc. Everytime someone see's the engine, it's a 35, or 41cc. I'm glad i'm not the only one confused. I would like to know what engine I will be putting in my plane. If I'm not sure of the engine size, it's not going in.

Well, there is always the brute force way of figuring out what size it is, but I can tell you it is NOT a 25. I have owned every model. Forget the numbers.

Why not bench run it. If it won't turn an 18 X 10 worth a hoot, which is recommended for a 41, then it must not be a 41.

If it purrs with a 16 X 8, it is a 25. (but I say again. it is not a 25!)

Bench run it!

Also, the 25 has a completely square head, looking at all the cooling fins from the side. The 35 and 41 are not square, looking from the side. See the picture I posted earlier.

Bill

Forget those serial numbers and model numbers. It's a 41cc according to your picture, possibly a 35, and definitely not a 25cc. The 25 has side exhaust and the spark plug points straight up out of the cylinder head.

Been working on these things for about a 100 yrs take my word for it. its a 41 . Early form of it was in a Frontier chainsaw.

On the small silver label on the underside of the engine, there is a "Model Number" and a "Serial Number". The serial number gives absolutely no indication of the engine's size. That may be part of the confusion. There is also another number on the tag that is marked as the model number of the engine.

Mr. Baxter --

The only tag affixed to my US Engines says "006956". There is no other tag affixed and the engine is still new - that's the way it came from Tower Hobbies. So how else, other than disassembling the engine and measuring, can one tell exactly what size this engine is? If by chance I were to want to sell it in the future, how would I prove to someone exactly what size it is?

Thanks for your help.

Here is a pic of the sticker on my engine.

Mr, Baxter --

I stand corrected! I went back and looked at the sticker again on my engine (was going to take a photo) and it does indeed show the model# starting with a "41". I guess I should have put on my glasses the first time I checked!

So it looks like rameleni1's engine IS a 25 cc engine. But I'm still confused. The photo he posted sure looks like my 41 cc engine and it doesn't have the "square head" that I thought the 25cc engine has (like the pic Bill Rademacher posted). But the sticker DOES show the model# beginning with "25".

Doesn't matter what the tag says, it's still a 41.