Hey everyone I have a 17 lrs with a screamin eagle 117 kit. Unfortunately I have high leakdown and since I’m gonna have to tear it down, I thought it would be a good time to upgrade my pistons/rings. My compression is 9.9:1 and I was thinking of bumping compression up to around 11:1.
what are my options? I don’t know much about pistons or brands. I’ve used weisco in the past on jet skis and sleds but what’s out there for harleys?

also wondering if I can buy a gasket kit for the 110, specifically for the cylinder to case gaskets. If I remember correctly the outer diameter of the 110 cylinders was the same as the 117.....it was a screamin eagle kit so I didn’t have to have my case bored.

thanks for any advice.

 

You don't mention what cams you are running, which should be part of the consideration when increasing compression above 10:1. And, pump gas during the summer on hotter days in slow traffic could be problematic too. You may have a local source of higher quality (no ethanol) and octane fuel, but you may not find that on the road.

HD has had some problems with some of their large bore cylinders not being round or even straight, so since you are having leakdown issues, I suggest you have a qualified machine shop use torque plates to check them thoroughly before deciding on pistons. And if boring is required, what is the limit of those cylinders. Personally, I like / use CP-Carillo pistons, but I believe Wiseco would be fine, but again, I would consider the effect of 11:1 compression on an air cooled engine being used on the street. Think about cylinder and head temperature, possible detonation and engine life. Also cranking compression pressure to consider the effect on hot starts (starter and battery) too.

Not sure on the gasket question, but I would suggest checking the piston deck height and using the correct head gasket thickness to set the desired squish band, which can have an effect on detonation. There are many online calculators for static compression and cranking pressure based on deck height, bore and stroke.

good luck,
Paul

 

thanks for the response. I haven’t decided what cams I will run. It has the se 259 cams from the 117 kit and I like the power but prefer to find something where the power comes on earlier in the rpms.

im a mechanic, but I’m by no means an engine builder so I know how to do the work myself, but not necessarily which components work well together.

I didn’t know that about hd’s cylinders. One thing is for certain, I won’t be boring them....if they’re jacked up I’ll buy new cylinders.

I just wanted to try to squeeze a little more power out while I’m in there as I’m planning to upgrade to a thunder max tuner as well but it sounds like I’m better off leaving it alone.

 

With that displacement you have options. Wood carbs make nice cams for making low end torque that last through the RPM range, as does TTS and others. If you aren't already, you might reach out to FuelMoto for suggestions on cams and parts if you end up needing anything, they have a nice selection and great support, and decent prices too.

thanks,
Paul