anyone perfomance/ reliability on the fatso : V-Twin Forum: Harley Davidson Forums

Breeze_tsmc · 10-16-2009, 07:56 AM

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

econnor · 10-16-2009, 02:24 PM

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.

wfolarry · 10-17-2009, 11:47 AM

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.

hightop · 10-17-2009, 12:11 PM

I'm not sure you'll be able to find a piston with the right compression height to use the 89" wheels in a fatvo, (designed for 4.25" stroke stock wheels,89" is 4.625" stroke) may want to research that before pulling the trigger on the cases.

hightop · 10-17-2009, 12:15 PM

Would result in a 109" motor with the 95" bore though, be pretty interesting. The other thing to keep in mind though is you'd need a 3.875 piston with an evo wrist pin bore (.792")

blackjackcustms · 10-17-2009, 01:37 PM

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"?

wfolarry · 10-17-2009, 01:57 PM

I also have a set of Jim's rods in mine that use the TC pin. You can use TC pistons & maybe find a piston that will work.

blackjackcustms · 10-17-2009, 02:02 PM

TC pin bore in the rods would be MUCH better. You can use any TC piston you want, that way.

I'm just cheap, and trying to use what I got.

harleytec · 11-05-2009, 11:16 AM

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!

beuch70 · 11-05-2009, 12:39 PM

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

FlyingGasCan · 11-11-2009, 10:35 AM

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.

dog155 · 11-12-2009, 09:08 AM

You certainly have plenty of info now to work with.Your next decision is too get whatever combo you pick assembled correctly,then get it tuned.Have fun and Good Luck

Hillside · 11-13-2009, 07:13 AM

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.

Scott

route66paul · 11-13-2009, 10:50 AM

Quote:

Originally Posted by blackjackcustms

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"?

rethink the sleeving or you will be sorry. my $.02

harleytec · 11-18-2009, 09:32 AM

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...............