Sportster Tech Talk

Re: loss of power

FX — Mon, 13 Jul 2009 16:47:54 GMT

It's been done..............................

Re: loss of power

framer1994 — Sun, 12 Jul 2009 17:20:13 GMT

yes I know the 10:1 is the compression ratio.I bought the cylinders and pistons as a kit,why would someone buy new cylinders without pistons??

Re: loss of power

FX — Sun, 12 Jul 2009 13:25:06 GMT

Framer,

The 10:1 compression has to do with what pistons you put in, not the cyls. Did you get a set of pistons/rings matched to the new cylinders? If the pistons are not 'forged', they must go into their dedicated cyl. I would still check piston clearance, and ring gap. If you're using chrome rings, they take longer to seat in. Sometimes as much as 1,500 miles. You mentioned maybe you didn't break it in right. Follow break-in procedure from your manual, and don't get on it till the plugs are burning well, and the compression is up to par.

Re: loss of power

framer1994 — Sat, 11 Jul 2009 22:21:31 GMT

the cylinders were ordered by me from a local shop brand new.I ordered them standard bore with 10:1 compression.I am sure they are standard bore as I am the one owner of the cylinders...........

Re: loss of power

FX — Sat, 11 Jul 2009 14:58:44 GMT

Framer,

That is an older bike. Unless you are the original owner, you can't be sure if the cyls., pistons, and bore are original. To do it right, and only one more time, you have to mic the cyls., check them for 'out-of-round', and check piston clearance. If you're not capable of doing that, take the cylinders and pistons to a qualified shop...........................Bet you need an over-bore, and new pistons/rings to do it right.................Pay me now, or pay me later...................

Re: loss of power

Ironhead — Fri, 10 Jul 2009 15:00:43 GMT

It is only an hour or so to pop them appart and check (just incase there is a scratch or two)

Re: loss of power

framer1994 — Fri, 10 Jul 2009 14:22:29 GMT

I will do both cylinders.they should be standard as he top end has less than 3000 miles right?I think it has an issue cause maybe I didnt give them time to seat or (break in)and just didnt seal properly...

Re: loss of power

FX — Fri, 10 Jul 2009 12:32:57 GMT

Framer,

Make sure you check the end gap, and adjust as needed. Be very careful installing the pistons, so you don't break any rings. It might be a good idea to mic the cyls. so you can order the right size ring set. I would do both cylinders.

Re: loss of power

framer1994 — Fri, 10 Jul 2009 01:26:00 GMT

thats what I was hopin to hear.gonna let her set till I get time to go get rings and put her together again.

Re: loss of power

FX — Thu, 09 Jul 2009 11:33:15 GMT

Also, in answer to your crank case pressure being excessive. With bad rings you're getting a lot of blow-by.

Re: loss of power

FX — Thu, 09 Jul 2009 11:03:38 GMT

Framer,

No, actually you were retarded by setting the timing on the TDC mark. A retarded engine will run hotter. Sounds like you have bad rings, as per your compression test with the oil......................

Re: loss of power

framer1994 — Wed, 08 Jul 2009 23:58:25 GMT

shot oil in and raised the front cylinder about 25 psi.I went ahead and test rode it after re setting timing on advance mark and I can actually feel the acceleration now.Big difference on power...

Re: loss of power

framer1994 — Wed, 08 Jul 2009 18:31:11 GMT

would that thing run bad that far out of timing and run hot also????I think I was setting static timin in the advance position using the tdc line on the flywheel.....

Re: loss of power

framer1994 — Wed, 08 Jul 2009 18:25:26 GMT

ya I am gonna do that tonight just ran out of day light last night....

Re: loss of power

FX — Wed, 08 Jul 2009 13:04:46 GMT

Framer,

You're right, that's too much of a difference.

I think you said you rebuilt the top end. If you didn't check the end gap on the rings, and they were too tight, you may have cracked one or more.

Here's how to determine if it's valves or rings: Take a compression test (throttle wide open). Then squirt some oil in the cylinders. If compression improves with another test, the oil has sealed around leaking rings and raised compression. If comp. stays the same, the valves are leaking.........................