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Sportster Motorcycle Motor - Top End Discuss Sportster Motorcycle Top End issues. Rockerboxes, Valves, Cylinders, Pistons, Rings, Lift Rods, etc...

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  #1  
Old 1 Week Ago
Jonzilla Jonzilla is offline
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Default Knocking in Front Cylinder Until Warm (Before & After Rebuild)

First post here. I've got a 2000 883 standard that the previous over converted to 1200. I bought the bike back in the Spring and after some carb tuning (was nasty rich when I bought it) it has run smooth and reliably for about 3,000 miles with me.

The problem is a clear knocking sound heard from the front cylinder until the bike reaches full operating temp (about 15 minutes of riding). It is a clear low toned knock in sync with rpms. I can hear it very clearly with a mechanic's stethoscope in the front cylinder and definitely at the exhaust flange. I've listened all over from top to bottom and the sound is not coming from somewhere else.

I figured for months that this was piston slap and finally decided to tear the top end apart and investigate. I found some scuffing on the front piston, intake side, and decided to do a rebuild. I couldn't feel any vertical movement in the wrist pin or lower rod bearings.

Saturday I finished the rebuild using Wiseco .020 over pistons, with my cylinders bored to match at a reputable machine shop. Everything went smoothly. I installed rocker lockers while I had it apart. I also slightly retarded the ignition since I'm still running the stock 883 module.

Problem is, the knock remains exactly the same as before. It seems unlikely to me that if it was piston slap before, that I'd have the same exact slap on the same cylinder with new piston and bore. I'm not sure what to look for next. It always goes away after it's good and hot. What else could do this and be heard in the areas described above?

Edit: https://youtu.be/EkHFVVh1Gxo Here is a short video of cold start up.

Last edited by Jonzilla; 1 Week Ago at 13:32.. Reason: Add Video
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  #2  
Old 1 Week Ago
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883 or 1200 heads?
Any witness marks on the inside of the rocker box or lid?
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  #3  
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Quote:
Originally Posted by Hippysmack View Post
883 or 1200 heads?
Any witness marks on the inside of the rocker box or lid?
883 heads. I used reverse dome pistons designed to work with 883 heads too. I didn't notice any witness marks in the rocker box or lid but will take it back apart soon enough to take another look at everything. I figure though, if anything was making contact in the rocket box area I'd hear it with the stethoscope. Still worth a look.
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Weak lifter?


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Quote:
Originally Posted by Bryan1976 View Post
Weak lifter?


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I was wondering that too. I didn't touch the lifters during the rebuild. I just wasn't sure if a bad lifter could make the hollow knocking sound I'm hearing and then go away after a few minutes. I need to post a video...
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I would replace the 883 Ignition Module - Find a 1200 module, even stock 1200 is better for the engine - but a SE1200 module is good (Q-curve) & there are programmable modules that allow better micro-adjustments to the curves...

See the Sportsterpedia section on ignition modules:
http://sportsterpedia.com/doku.php/t...k:evo:engctl01

Do a compression check - This is important information...
http://sportsterpedia.com/doku.php/t...:evo:engmech03

Do you have a report from before the rebuild?
Did you do a check immediately after the rebuild?
You definitely need one now...

This verifies operation of the cams, lifters, rods, rockers, valves, rings, etc...


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Last edited by IXL2Relax; 1 Week Ago at 20:16..
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Quote:
Originally Posted by IXL2Relax View Post
I would replace the 883 Ignition Module - Find a 1200 module, even stock 1200 is better for the engine - but a SE1200 module is good (Q-curve) & there are programming modules that allow better micro-adjustments to the curves...

See the Sportsterpedia section on ignition modules:
http://sportsterpedia.com/doku.php/t...k:evo:engctl01

Do a compression check - This is important information...
http://sportsterpedia.com/doku.php/t...:evo:engmech03

Do you have a report from before the rebuild?
Did you do a check immediately after the rebuild?
You definitely need one now...

This verifies operation of the cams, lifters, rods, rockers, valves, rings, etc...


IXL _______ >>>> My Motorcycle Chronicles Are Here <<<<
For FREE Sportster Tech Info from the XLForum:
Explore The Sportsterpedia - The Best Kept Secret on the XLForum!
I have not done a compression test. I don't have a gauge but if Autozone has one I'll get that done this evening.
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Compression test just done at full temp:

Front cylinder 165psi
Rear cylinder 162psi
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Compression is good. Did you do heat cycles and 500 mile break-in yet?
Or are you hearing noises on a fresh build after break-in?

Piston slap isn't usually a low toned knock.
Low tones are usually in the bottom end... and first thing thought of is rod or crankshaft bearings.

You'll have to dig deeper.
See Hunting Down Sportster Noises in the Sportsterpedia. Lots of noises to chase there.
http://sportsterpedia.com/doku.php/t...k:ref:genmsr05

Crank bearings turn smooth by hand , no bumps or noises?
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Jonzilla Jonzilla is offline
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Quote:
Originally Posted by Hippysmack View Post
Compression is good. Did you do heat cycles and 500 mile break-in yet?
Or are you hearing noises on a fresh build after break-in?

Piston slap isn't usually a low toned knock.
Low tones are usually in the bottom end... and first thing thought of is rod or crankshaft bearings.

You'll have to dig deeper.
See Hunting Down Sportster Noises in the Sportsterpedia. Lots of noises to chase there.
http://sportsterpedia.com/doku.php/t...k:ref:genmsr05

Crank bearings turn smooth by hand , no bumps or noises?
I went through the heat cycles and am 200 miles into break in. To be clear, this noise was there before and after the build. No change.

Would rod or crankshaft bearing quiet down after warmup? That is what is throwing me off. It sounds normal after a few minutes. This has been the same for about 3,000 miles since I bought the bike. Also I don't hear any noise down low on the engine with my stethoscope. Basically nothing below where the cylinder meets the case. It all seems to be in the cylinder area and also exhaust flange.

I did feel for slop or vertical play in the rods while I had the engine apart but I didn't rotate the crank repeatedly or anything. Though wouldn't crank or big end bearing noise be heard down low with the stethoscope?

This is my first engine rebuild and I'm realizing I could have checked a lot more stuff than I did while I had the chance. Live and learn. I'm not new to wrenching on all my bikes but this was the deepest I'd ever gone.
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