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anyone perfomance/ reliability on the fatso

17K views 21 replies 14 participants last post by  HOG977 
#1 ·
Ok, I have learned after purchasing my 91 evo that I bought one of the weak case years. (I should have read before I bought but that wouldn't be my luck) I broke the pinnon shaft and will have to rebuild. I bought the s&s 89 stroker kit to leave the stock bore BUT now I am told that the race on the pinnon side is loose and needs to be replaced aswell. All of this I learned was an issue from most of you, (Thanks!)

My new question is I see that ultima makes a fatso case and I have my wifes old 88 twinkee cylinders and heads. I see a fatso case going on ebay for about 500.00,,,,,does anyone know someone who has put some hard miles on this combo motor?

My motor is already apart and the s&s 89 kit is in the shop so if there is a better mouse trap out there now is the time for me to pull the trigger.

Thanks
 
#2 ·
I often ride with a guy that has a Fatvo in his FXR. He used the case from Sputhe. Heads were worked over by Baisley, hot cams, all the right parts. He beats on it constantly around town, and rides it cross country. I have never heard him say one bad thing about his Fatvo.
 
#3 ·
I had one in my bike for 5 years. Never had a problem. Have it on the bench now. Put the original motor back in to do some 'hoppin' up' work on the Fatso. Or sell it. Can't make up my mind. Reliability doesn't suffer. Mine has the Sputhe cases. The heads needed the intake pushrod holes welded & relocated. Pushrod tubes need trimming to fit right. That's about it. I don't know how the Ultima is set up. Sputhe cases use stock flywheels.
 
#6 ·
I am building a 100" stock stroke motor with ultima 3.875" piston. They needed the domes cut off ( easy ) and then they sat about .080" lower in the bore. I had my machinist cut down the cyl.s, and he chewed up the liner on one of them ( gdamn), so now he's going to resleeve. I am tempted to use a different set of cyl.s I have, and a set of 4 3/8" flywheels to cover the diff.

Anyway, my point is, the Ultima 100" pistons are the correct bore, and the correct pin bore as well. They have a dome to match Ultima heads, and have a slightly lower deck hieght. Perhaps with thicker base gaskets, and the lower deck, you could get them to work @ 4 5/8"?
 
#14 ·
rethink the sleeving or you will be sorry. my $.02
 
#9 ·
Case replacement with the best!

If you are considering case replacement, you may want to look at DELKRON. They are the best cases you can buy and have been in the business a long time. You know if you go with a fatso case you will need a .250 longer pinion shaft? Because of the bigger bore. DELKRON also has complete short blocks with flywheels already installed. Been running their set-up for years with a 95" TC top end (=100 CI) and love it!
 
#10 ·
i have a 89 in in my 90 fxrs.runs strong tho low and mid end,flats out on top end,had stock cases and they cracked on the oir return passage and im installin s&s big bore cases.got it apart and found that the heads where never touched,so there in the shop havin the opened up,biger valves,c c them.the shop thats doin the work said that the heads will give me the top end back,when it was dyno it only had 77 horse and 87 tq.hope it will be in the mid 90s when back together
 
#11 ·
I'm thinking of building a Fatso motor right now and I'm looking at various combos. My bud used to work for Jerry Merch and has a lot of experience building this motor style. I may buy a Delkron block and build a 120" with R&R or Baisley heads. A couple friends have Fatso motors in their bikes and they work great with no issues.
 
#13 ·
Use your crank, bore the cases, contact Axtell sales and get a 4 1/8" cylinder kit and get it to 124", and be done with it.:woohoo:
Scott
 
#15 ·
lots of options

There are a lot of options out there, but if you go to delkron's website you can see that they offer more than anyone for the fatso set-up. They even have a service to relocate your pushrod holes. I'm not sure about the other guys, but at least delkron is made in America...............
 
#16 ·
I got a Fatso motor in my 88 FXSTC. No idea how many miles on it cause I converted to an aftermarket gas tank years ago and got rid of the dash, speedo and such. Motor runs strong, breaks the ass end loose like nothing. I've had that motor probably 7-8 years, it was built by a company called Milwaukee Performance on top of cases from a merch 120.
No motor problems, but all the torque kept cracking my primary case, right around the stator, compensator sprocket area. Fixed that with a carlini torque arm(after 2 or 3 inner primary's) then I sheared that silly little keyway off my mainshaft that holds the clutch in place,prolly 3 times b4 I finally was able to upgrage to a splined, later style clutch setup. LOVE the motor though, just that cheesy 88 drivetrain could not handle it.
 
#17 ·
Yea,I saw and have heard alot about delkron, but I had a set of delkron's 91cc heads on my 2001 FLH and It broke a valve guide causeing a lot of damage, I never could find out who's guides delkron used and as a result my shop kept having to cut down guides and make them fit. IN two years I went thru three as it kept leaking oil so Delkron is not in my list of favorites.

I ended up just staying with the stock cases and the sidwinder kit. I probably spent the same money as the fatso the unknown and the fact that my shop had never attempted this setup helped in my decision.

I'm breaking it in slowly and it feels strong so far..
Thanks for all the input
 
#18 ·
Delkron Parts

I understand there were some issues with the earlier head design that used the cast iron guides, but they now use manganese bronze guides and coated valves, their tolerances seem to be a lot closer now too. I've been runnin their stuff on my fatso for a couple years now with no worries!:chopper:
 
#21 ·
A clearance issue where? I don't know why ppl are scared of this motor, it's not much different than putting a shov top end on a pan. Well maybe a bit more difficult but not much. The biggest prob is knowing what fits what. A little cylinder boring and a 100" Indian piston fits right in and then a little cylinder shimming (about 1/8" if you're running stock evo stroke) and it's ready to button up. The easiest setup is to use the early 5 piece wheels and change out the pinion shaft with the longer shaft or you can go the hard way as I did and use the 3 piece wheels then machine the pinion gear to line up with the cam gear. You have to use the early nose cone and evo pushrods/tubes in either case. You can stroke this motor out to HUGE cubes by altering the shims height and top tube frame rail depending on how much you have to shim, 1/4" shimming would make it tight in a stock frame but do-able. 1/8" fits nice. By the time you get the motor together you got about $2500.00 in it. Not bad for a new 100" motor with new cases. Go Ultima cases or if you want the best go Sputhe, Delkron would be my third choice. Ultima cases are made for small diam wheels so if you're using stock evo wheels you'll have to grind the case wiper to fit. Not a big deal if you have a little ingenuity and a drill press with a drum sander. Once you build one of these motors you'll wonder why no one else is building them. You end up with the strongest hd bottom end and the newer top end and the cheapest motor build, how you gonna beat that?
 
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