Boxerworks.com

Patient: 81 r100rs

At low idle I'm hearing a knock coming from the centre of the engine it seems.
The knock goes away at normal idle and above.
The knock seems to be each revolution.
There is also some pinging/engine knock? at about 4- 5000 under load. That may be due to recently changing the position of the slide needle from the third to the second notch. Plugs don't show lean running.

I did find an issue with my round oil filter o ring back in June. I stuffed up a bit............

I'm thinking big ends or crank.
Valve clearances are good

I thought you recently installed a new crank?

gspd wrote:I thought you recently installed a new crank?

Yes. I did. I'm not too happy. They don'r knock for nuthin'
I think I need to pull the jugs and check the big ends at least.

Usually if it's knocking and the oil pressure is good, it's a con rod big end bearing.
Can you tell which side sounds like it's knocking?
When it sounds like one side knocking, it' s usually the other side big end bearings that are shot.
Either way, check both sides.

Failed main bearings usually cause oil pressure problems before they become loud.
Did you hear a knock when your rear main bearing failed?

Was your replacement crank new, used or reground?

Maybe it's time to take the ole 109 off the road and do a full restore mate? Spend a year or two bring it back to what it was like when first bought?

gspd wrote:Usually if it's knocking and the oil pressure is good, it's a con rod big end bearing.
Can you tell which side sounds like it's knocking?
Sounds like the left.

When it sounds like one side knocking, it' s usually the other side big end bearings that are shot.
Either way, check both sides.

Failed main bearings usually cause oil pressure problems before they become loud.
Did you hear a knock when your rear main bearing failed?

No, just the oil light staying on too long.


Was your replacement crank new, used or reground?

Very good s/hand from Nick in NZ. It basically measured full size.

Cold engine oil light test this morning. It was taking about 10> seconds to come back on.
The time lessened with more tests as the engine warmed.
Later today I'll ride it to operating temp and assess again.
I still think the jugs will need to come off.

If the pistons are too small they will "slap" and sometimes quiet down as they warm up, very quickly. Some pistons designed with short skirts are more prone to this. If you have changed pistons a difference in designs may be a culprit.

Warm it up (hot) and then dump the oil.
You'll see it right away in the oil if it's a bearing;
It'll look like it has metallic paint in it.

If the oil looks perfect, it could be something else making the noise.
Does it make the noise with the dipstick removed?
If not, check if the breather hose is collapsed.

Clutch in, clutch out, no difference?


If you do take it apart there's no need to separate the head from the cylinder.

gspd wrote:Warm it up (hot) and then dump the oil.
You'll see it right away in the oil if it's a bearing;
It'll look like it has metallic paint in it.

20 minute ride and dumped the oil straight away. 2 small bits of grey silicone (valve cover gasket) and 1 small piece of black plastic, less than 3mm, it looked like a piece of timing chain guide

If the oil looks perfect, it could be something else making the noise.
Does it make the noise with the dipstick removed?
If not, check if the breather hose is collapsed.

It sounds like an army helicopter is hovering above my head with the dipstick out

Clutch in, clutch out, no difference?

Normal clutch noises


If you do take it apart there's no need to separate the head from the cylinder.

I've refilled with Penrite HPR30 20 w 60. my usual oil.
I did have Castrol GTX2 20 w 50 in it, and it was very thin when it came out....... not even 4,000 k's on it.
The bike ran quieter with the new oil but I'll defer judgement until the next test ride.
At least there was no metal in the oil. Not even teeny bits of silver.[/quote]

ME 109 wrote:
It sounds like an army helicopter is hovering above my head with the dipstick out

I didn't mean for you to ride it that way, just listen to it while revving it in neutral, with a rag lightly scrunched up over the hole.
A big end knock will remain audible over the cacophony of normal noises.
A breather induced knocking noise (if that's what you have) will disappear.