I purchased a 1999 fatboy a couple weeks ago. As most of you probably know, 1999 was the last year of the 80ci EVO motor in the Softails. Today I went to change the spark plugs so I went to the dealer and asked for plugs for a 99 Fatboy. I took them home, pulled the old ones out only to discover they were the wrong plugs. I pulled out my parts catalog and found that they were in fact the correct spark plugs for a 99 fatboy... but not my 99 fatboy! Confused, I went back to the dealer and explained the situation and showed him the spark plug I took out. He looked up the numbers and said it was the plug used in the 88ci Twin Cams. He said what most likely happened was that my bike was put together toward the end of the year when the transition from the EVO to the Twin Cam was taking place and I ended up with a Twin Cam motor in my 99 Fatboy.

Has anyone ever come across this... or similar happenings??? How do I know for sure that is what the case is and that my motor is in fact a Twin Cam?

 

I highly doubt that the info the dealer provided was correct. It's easy to visually recognize a Twin cam from an Evo. Make this simple on everybody and just post a picture of the right side of the engine. Look at the differences in the Cam Covers.

TWIN CAM


EVO

 

As you can see the lifter blocks are set wide on the Twin Cam, where they are almost together on the EVO. Could be somebody put the wrong plugs in your bike. There is one other way to tell, if yours sounds real good, and runs real good, its probably an EVO. LOL

 

I never thought of that... heres a pic! I can tell tho by looking at the pics you posted that it is in fact an EVO tho. I dont understand the plugs being different then. Its not that someone put the wrong plug in, the threads are 2 different sizes. It does have Screamin Eagle heads installed on it... could that be why the different plugs? Youll have to excuse my ignorance, Im kind of a newbie and not real knowledgeable about motors!

 

I don't know for sure, but I am guessing that the Screaming Eagle heads would be why the plugs are different. Can't think of any other explanation.

 

umm, the twin cam engine is attached to the tranny....no seat post.. the frames are not the same and not possible to put a twin cam into a evo frame..possible to put 88 twin cam heads on an evo i think so, cuz evo pipes can fit on a twinkie

 

OK, now that we've confirmed that it is an Evo, you will find more Evo savvy folks on the Evo forum. Answers are a little slower coming, but there's some folks there that are very knowledgeable about these engines and I'm pretty sure they will be able to solve your mystery.

Here's a link to the Evo forum: https://www.hdforums.com/forum/evo-classic-models-84/

 

Thanks for all the help guys! Ill head on over to the Evo forum from here and see what I can find out!