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twin cam knock help

16956 Views 16 Replies 7 Participants Last post by  05standard
hi all, well I have a 05 fxsti 88 twin cam with a knock only at idle.dealer checked compensator and all in primary,no issues found,told me it was a rod knock had to be torn down.i finished pulling it apart last night and don't see anything obvious.i pulled plug wires while running before teardown and knock was gone while rear plug wire off?rod bearings front and rear move side to side the same,nothing I can feel up and down,wrist pins in rods and pistons feel good???? any suggestions im loosing my marbles:what?
thank you.
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oh yah, it has 23k miles and is stock
If you pull rear plug wire while running, compression stroke is minimalized due to no combustion. (explosion forcing piston down)

Could be rod bearing, but could be skirt slap, or broken skirt.

Rod bearings also get louder or more frequent with higer RPM. Is that the case?

Are your rocker bushings worn?

Is your cam chest in good condition?

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I don't hear it at higher rpm only idle and just off idle,i don't feel any up and down movement in the rod bearings or the wrist pin bushing or wrist pin in the piston.would cam noise go away pulling one plug wire while running?the only thing I haven't checked at this point is the piston in the cylinder.i figured that I would find something obvious in the rear cylinder,got me stumped
rocker bushings also feel good,same front and rear
Might be of some help and may not transfer to street bikes, but I always was told with dirt bikes that side to side rod play or up and down was not as big an issue as axial or rotational play. With the piston / rod in your hand try rotating the rod clockwise/counterclockwise.
hahahah RED LINE IT till she blows hahahahaha
check all the easy stuff first then check piston.
BUT i still say RED LINE IT till she blows. (i just love pushing there limits you would be amazed at how far you can push them) once had a gmc v6 threw a rod out side of the block tied it up poured in some 10wt oil 30 gal can(i found it haha) and drove that thing home about 50 miles or so.
so I ordered s&s 97 big bore kit,tappets,adjustable push rods,roller rockers parts will be here tomarrow,also ported my heads while they are off and had my machine shop do a valve job.will see what happens Monday,hopefully its quiet if not then I go deeper:eek
Check valve guides for wear tolerance. Have been noise issues with worn guides.
My money is on the lifters, especially if it does it when hot at idle. Drove me nuts on my old sporty because I had replaced them and figured it must be something else. I went back to stock lifters and ditched the cranes and it was cured. : )
Most T/C problems stem from the cam chest area......
so I pulled out my cam chest and don't see to much.tensioners are good,cam bearings good,cams good,oil pump ???? has quiete a bit of scoring on outer pump part to cam plate and on cam plate.if I could get some info on oil pump scoring that would be awesome.doesnt look bad enough to make a knock but?????, thank you
I defer to the gurus (as always), but logically, it seems that with oil pump scoring you might have to consider the possibility of crankshaft runout or thrust movement.

Oil pump scoring is normal and common.

Oil pump drive is off end of crankshaft. This is why alignment screws are used to install it, as to center it as much as possible, and prevent excessive wear to the pump body.

If the runout is within spec, the oil pump will work, but will score the aluminum body (steel gears) as the crank moves, especially the farther the run out is. Nature of the beast. Shops sell $300 oil pumps to people using the scoring as the reason why. Not necessary. There's an acceptable wear depth.

It will not knock no matter how bad it is. If it's that bad, it'll wear the pump enough to lose pressure.

If there's enough clearence to "knock" you have a scissored crank.

If the pump bolts are loose, you'll hear a knock, but also you'll lose oil pressure, as the cam plate seal is breached.....

If the cam chest is fine, then your knock is likely internal.

BUT.....I'd check the primary compensator bolt and clutch hub nut before pulling the engine totally. As well, chain tension.

Stranger shit has happened.....
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Sound info from ol' Dave as usual.
Could be from the comp sprocket?
great info. and as always I really appreciate it.the dealer said everything in the primary was good,but I have to check it myself to be sure.will post my findings thanks again
so finally after all my bulls*&t big bore kit,pulling cam chest out,heads redone,lifters,adjustable pushrods,roller rockers and shafts,dealer inspected everything in primary first and told me it all EXCELLANT and it was a engine knock and had to be torn down at $1500 to $4000 I find the rotor for the charging system splines all sloppy,$95.01 at a different dealer and all is good now what the f.and not to mention almost 1 month of lost riding:fitz well hopefully this may help someone else?
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