Knock, knock......

[PaulE]

Greetings to all.
This is my first post to the forum although I have been lurking here for months. And I thank all the contributors for the volumes of great information.
I have a '99 ST1100 and it has an engine knock (strange as it may seem for this bike).
It has 40K kms on the clock and appeared to have been well looked after when I bought it a few months ago.
It can only be heard when fully warmed up, no knock when cold.
Loading up the engine (slipping the clutch with brake on) doesn't make it louder, but the knock increases in frequency with rpm's.

Here's what I have done so far;
Drained the gas and filled with 91 octane.
Changed spark plugs (I know, that never fixes anything).
Replaced the the oil with Amsoil 10W40.
Removed the carbs, they were spotless inside.
Replaced the coolant fitting "O" rings while the carbs were off.
Removed all the PAIRS equipment and the vacuum fuel valve.
Sync'd the carbs (single gauge method) they were pretty close to spot on already.
After each one of the above items, I re-checked for the knock and each time....still there.

I would be most grateful for any ideas or diagnosis. Please don't tell me it's a rod bearing
I'm not thrilled at the thought of following in Allen Millyard's footsteps this winter, but if I must, thank you in advance Allen.

The link below is for a YouTube video (and audio) of the knock. I couldn't figure out how to post a video here, maybe its not possible.
I held a mechanic's stethoscope probe to the engine near #2 cylinder and held the earpiece up to my phone's mic. Hope it helps.

Cheers, Paul
Nova Scotia

 

[Sunday Rider]

Welcome Paul!
Do you still hear the knock when you pull the clutch lever in or does the sound change at all?
mine does this at low rpms and has done it since I’ve owned it. I am the second owner.

 

[PaulE]

No difference whether clutch is in or out, unfortunately.

 

[red one]

Thats strange. When mine is dead cold and i try to ride it before its warm it will make all kind of strange noises but when it warms up its smooth as silk.

 

[Erdoc48]

Interesting…doesn’t sound like a knock like internal engine damage, more like a ‘pop’ as you would hear with an exhaust leak (maybe the exhaust gasket), no?

 

[DannoXYZ]

Definitely not detonation/pinging since that happens under higher loads.

1. do compression test

2. measure valve clearances

 

[ST1100Y]

I have a '99 ST1100 and it has an engine knock (strange as it may seem for this bike).
It has 40K kms on the clock and appeared to have been well looked after when I bought it a few months ago.
It can only be heard when fully warmed up, no knock when cold.

Chasing a similar low frequency thump on my '00 right from day one! (by now 130,000km on the clock)
As well only when engine is really hot (like after racing up a steep twisty mountain pass), but vanishes when raising RPM or gently engaging clutch (could as well simply drown in the engine noise thoug...); hasn't gotten worse over the years, hence I'm reluctant of knocking the engine apart for a full rebuild...
(OTOH had my previous '92 ST1100 no such issues at all, it also felt smoother, zero vibes... so I suspect a slight decrease of assembly quality/cutbacks in the last production years... also the paint wasn't as flawless anymore, neither on the bike delivered, nor of fairing parts ordered as spares... color variations, drops, decals not properly aligned, parts out of shape, etc...)

Brainstormed with my mech a couple of times... suspects are:
- crank sided pulley slightly loose (wedge, splines), would be an easy fix to remove & apply some Loctite...
- borderline specs on mains or big-end bearing, see engine rebuild...

There was a YouTube vid about a Britt who also chased a silent knock, found one mains bearing clearance slightly over spec, installed new shells one size up, seems to have cured it...

 

[PaulE]

Thank you for your replies.
Through a stethoscope I don't think an exhaust gasket leak would be all that noticeable. To the naked ear it's definitely not a "pffft" sound.
I suspect my recording doesn't accurately represent the noise, it sounds like an internal knock.
Dannoxyz, I suppose a compression and valve clearance check wouldn't hurt but I've never heard of those being the source of an engine knock.
The bike runs great otherwise.
And ST1100Y, the Britt you are referring to is Allen Millyard. His YouTube videos are the sole reason I may fearlessly plunge into a teardown.
I think my options at this point are ride it until something lets go, or put it away until winter and take it apart.
I'll keep you posted on further findings.

 

[Erdoc48]

Don’t forget the tea and cupcakes if you dive in like Allen Millyard and be ready to say ‘I’m really pleased with that’.
Those we’re entertaining videos.

 

[PaulE]

Baaaahhhh, ha,ha, ha.
Yes, and I've been looking for a hedgehog to keep as a pet, although being in Nova Scotia I may have to settle on a porcupine ....oh, and a beer.

 

[ReSTored]

A question Millyard never really spoke to or addressed was if the wrong size bearing insert created a situation that absolutely had to be addressed, or was it his dedication to excellence compelled him to tear the engine down to fix it. The slight knock you hear doesn't sound too bad. What would be the consequences of just ignoring it, in particular on a 25 year old bike with just 40k km on it?

 

[PaulE]

ReStored, the impression I got from Allen's problem was that the factory installed a slightly oversized bearing which was in contradiction to what their codes called for.
And I also think you are right in believing that his perfectionist nature contributed to his need to find the problem.
In my video the bike isn't fully warmed up yet and the knock is at about half of it's potential intensity. When I'm stopped at a traffic light I find myself looking around to see if I am getting any strange looks. I'll try to get a better audio perhaps without the stethoscope.
And for DannoXYZ, I did a cold compression test this morning and the numbers from cyl 1 to 4 were; 125, 120, 125, 126. Not perfect but within spec (if 120ish is normal). I'll try a hot test next. BTW all the spark plugs showed identical colouring.
If it is a big end bearing and I continue to ride it, it will undoubtedly do more damage. In that case I would need to find a used engine and nice ones are going for around $1000 (+shipping).
So, whether I run it to death or pull the engine and repair it, either way an engine gas to come out and an engine has to be re-installed. Infinitely cheaper to repair it.
Thanks for all the input so far.
Cheers,
Paul

 

[Ron]

Please excuse my ignorance. All I've ever done to an 1100 motor is routine maintenance-change out fluids, filters, brake pads, bearings and tires.

Why would you need to remove the motor to replace a crank bearing on 1 piston rod?

 

[DannoXYZ]

Please excuse my ignorance. All I've ever done to an 1100 motor is routine maintenance-change out fluids, filters, brake pads, bearings and tires.

Why would you need to remove the motor to replace a crank bearing on 1 piston rod?

It may not be rod bearing, but main crank bearing. Rod-knock may be cause by bearing wear from poor oiling. Which takes time. But in this case it may be assembly error from factory when installing main crank bearing. So case halves needs be separated just to measure them. Then if clearances are off, replace it.

 

[PaulE]

Mystery solved....sort of.
I opened up the oil filter that I had replaced last week. There's some glitter in there.
I then dragged a magnet over the stuff and it's mostly magnetic. I think that pretty much narrows it down to the crankshaft, unless anyone has another theory.
If it is the crank, the motor is probably junk.
I think I suspected all along it was a rod or main bearing. I was hoping someone on the forum might have some advice for a simple fix.
The oil that came out of the bike was pretty clean, so I don't think the filter had many miles on it.
Here are some pics of the filter material.

 

[Sunday Rider]

That can be anything on that filter. I say ride it until it doesn’t. I don’t recall of any ST1100 having a failing crankshaft, especially at the low mileage. I think if we didn’t watch Allen’s videos we’d be none the wiser and just put it down as one of those typical ST1100 quirks. But that’s me.

 

[bdalameda]

Mystery solved....sort of.
I opened up the oil filter that I had replaced last week. There's some glitter in there.
I then dragged a magnet over the stuff and it's mostly magnetic. I think that pretty much narrows it down to the crankshaft, unless anyone has another theory.
If it is the crank, the motor is probably junk.
I think I suspected all along it was a rod or main bearing. I was hoping someone on the forum might have some advice for a simple fix.
The oil that came out of the bike was pretty clean, so I don't think the filter had many miles on it.
Here are some pics of the filter material.

Being that the gearbox is lubricated by engine oil it is not uncommon to find metallic debris in the filter or on a magnetic drain plug. Gearboxes can produce a lot of particulates especially after a good missed shift and a good crunch into gear from the gear dog engagement.

Even if your bike has had the carbs synched it still could be one cylinder not pulling its weight from an improper mixture setting at idle. The ST1100 will produce a noticeable knock when one cylinder is not firing at idle, the sound is similar to a rod knock. It could be as simple as a mixture adjustment or a plugged idle jet or idle circuit. Float level can also really affect the idle mixture. I have also seen bad plug caps cause this kind of knock.

Try pulling each plug wire cap when the engine is at idle and see if you see a noticeable drop in idle. If you pull one cap off and see no idle change you have found what cylinder id not pulling with the rest.

Something else to check is the enrichment(choke) linkages. Make sure all four plungers are fully seating when the lever is off. Lubricate the linkage and make sure the cable operates smoothly. I have seen these linkages cause issues many times having one plunger not seating all the way. This will cause a rich mixture on one cylinder that will go away when the rpm rises as the enrichment circuit only works at or near idle rpm.

 

[PaulE]

Wow! Thank you. I had completely forgotten about the transmission.
As for each cylinder "pulling it's weight" I checked the exhaust pipe temps after a few minutes of idling. The temps cyl 1 through 4 were; 140, 340, 180, 192. Googling "what causes high egt's tells me that it could be a lean condition or a rich condition, depending on which article you believe. My 2 stroke experience tells me that lean = hot, but I don't know if that holds true for 4 strokes.
Cyl's 1 and 2 are the extremes, but it looks like each one is firing. Also, all the plugs are identical in colour which would indicate they are all working. I should mention though that I set all the pilots out 2 turns as someone on the forum suggested. I don't have an adjusting tool and was planning to have a dealer set them up.
Another notable clue is that it only knocks when the engine is hot, no knock when cold. That should also rule out the non-firing cylinder theory.
I definitely will try pulling the plug wires one at a time and check the choke linkages as suggested. I also want to re-check the compression with a hot engine. The 120 ish PSI readings I got on a cold test are less than impressive.

 

[Obo]

Welcome and congrats from jumping from lurker to poster. Hope you get it sorted soon, and that it's a relatively easy and inexpensive task!

 

[Firstpeke]

There's a good Alan Millyard video series on YouTube...