Engine makes a crack like sound

sosdingle · Mar 31, 2017

Hello again .
Well , I got around to doing a compression test this evening. A bit of bad news on that front. Compression readings as follows,
cyclinder no. 1 , 150psi.
Cycl no. 2, 175psi.
Cycl no. 3, 185psi.
Cycl no. 4 180psi.
So ,I have a problem with cyclinder no. 1.
I did the teaspoon full of oil test which resulted in the compression jumping up to 200psi.
I think this means the valves are ok. That leaves piston rings and head gasket.
I must get my hands on a leak down tester to determine exactly where the compression is being lost.
As regards the snap crack at a very hot restart. I have put that down to pre ignition. Unless this lack of compression in one cyclinder is a factor.

dwalby · Mar 31, 2017

sosdingle said:
Hello again .
Well , I got around to doing a compression test this evening. A bit of bad news on that front. Compression readings as follows, cyclinder no. 1 , 150psi.
Cycl no. 2, 175psi.
Cycl no. 3, 185psi.
Cycl no. 4 180psi.
So ,I have a problem with cyclinder no. 1.
I did the teaspoon full of oil test which resulted in the compression jumping up to 200psi.
I think this means the valves are ok. That leaves piston rings and head gasket.
I must get my hands on a leak down tester to determine exactly where the compression is being lost.
As regards the snap crack at a very hot restart. I have put that down to pre ignition. Unless this lack of compression in one cyclinder is a factor.

I thought the teaspoon of oil test confirms bad rings and/or piston seal in the cylinder. The oil helps seal the area between the piston and cylinder. If the head gasket were bad I don't think the compression would recover with the addition of oil, would it?

sosdingle · Mar 31, 2017

dwalby said:
I thought the teaspoon of oil test confirms bad rings and/or piston seal in the cylinder. The oil helps seal the area between the piston and cylinder. If the head gasket were bad I don't think the compression would recover with the addition of oil, would it?

You are absolutely right. Would it be unusual for piston rings to be worn or damaged in just one cyclinder. Wouldn't you think they would all wear more or less the same amount. There is a significant difference in compression readings from the other cyclinders.
If it is indeed piston rings, it's probably not worth a strip down. Considering age ,mileage etc of bike.
I guess that's it's unlikely that a piston ring is stuck.

Bmacleod · Mar 31, 2017

Although 30 p.s.i. is a significant difference, a compression test isnt the most accurate test. Im not sure of the 1100 but on the 1300, the low limit is 142 p.s.i., so i would think it is still within spec. The difference is the more important factor though, so I would listen to the bike run and if there is a noticeable imbalance in the the engine caused by a weak cylinder, then I would start to weigh my options. If it isnt noticable, id just ride it, especially when , like you said , its not worth rebuilding.

Bmacleod · Mar 31, 2017

If its really eating at you and/or you really want to dig around, you could drop the pan and see if there is a chunk of piston skirt in there. It could explain the noise and a low compression reading

dwalby · Mar 31, 2017

sosdingle said:
You are absolutely right. Would it be unusual for piston rings to be worn or damaged in just one cyclinder. Wouldn't you think they would all wear more or less the same amount. There is a significant difference in compression readings from the other cyclinders.
If it is indeed piston rings, it's probably not worth a strip down. Considering age ,mileage etc of bike.
I guess that's it's unlikely that a piston ring is stuck.

you didn't mention in the original compression stats, did you test each cylinder several times to avoid any mis-measurements? Any chance that 150psi reading was a fluke?

I agree with Bmacleod comments, its probably not severe enough yet to go through the trouble of rebuilding it.

saddletramp8511 · Mar 31, 2017

For what its worth watch what you eat and quit blamin it on the bike.

SMSW · Mar 31, 2017

Bmacleod said:
If its really eating at you and/or you really want to dig around, you could drop the pan and see if there is a chunk of piston skirt in there. It could explain the noise and a low compression reading

I would doubt you could break off a piece of piston skirt and not have other, more severe problems. Besides, the OP mentioned the sound reoccurs - so unless he is experiencing ongoing piston skirt deterioration (a rather extraordinary situation) this is not the problem. If you lost a significant piece of the skirt, would not the piston rock a bit and score the heck out of the cylinder wall?

bdalameda · Mar 31, 2017

It can be quite normal for one cylinder to read low on compression if it is running overly rich due to a carb problem or has a bad plug and is misfiring. The unburned fuel washes the oil film off the cylinder walls and reduces the sealing of the rings which will cause a compression test to show lower pressure than the other cylinders. Having 150 psi is not that bad and I think everything is probably fine -if the compression improves with a drop of oil this is probably what has happened especially if the engine is not burning oil. Also did you hold the throttle wide open during the compression test? This is important to get accurate readings.
Another reason for lower compression on one cylinder of a high miles engine can simply be carbon and varnish buildup in the piston ring lands causing the rings to stick and not fully seal. A good engine oil additive like Archoil 9100 that will slowly free up the rings may solve your problem and Archoil 9100 won't harm wet clutches. You must be careful with other types of really aggressive engine cleaners and desludging type additives as rapidly dissolving the varnish and carbon can also loosen up a lot of other accumulated stuff and possible plug oil passages. Do you run synthetic oil or petroleum based oil? Usually the carbon and varnish sticking of rings is more prevalent with high mileage engines running petroleum oils.

sosdingle · Apr 1, 2017

Bmacleod said:
Although 30 p.s.i. is a significant difference, a compression test isnt the most accurate test. Im not sure of the 1100 but on the 1300, the low limit is 142 p.s.i., so i would think it is still within spec. The difference is the more important factor though, so I would listen to the bike run and if there is a noticeable imbalance in the the engine caused by a weak cylinder, then I would start to weigh my options. If it isnt noticable, id just ride it, especially when , like you said , its not worth rebuilding.

I agree. When the bike is running the imbalance is barely noticeable,if at all. Thanks

sosdingle · Apr 1, 2017

dwalby said:
you didn't mention in the original compression stats, did you test each cylinder several times to avoid any mis-measurements? Any chance that 150psi reading was a fluke?

I agree with Bmacleod comments, its probably not severe enough yet to go through the trouble of rebuilding it.

I tested each cylinder twice to be sure, and the offending cylinder a third time with the oil.

sosdingle · Apr 1, 2017

bdalameda said:
It can be quite normal for one cylinder to read low on compression if it is running overly rich due to a carb problem or has a bad plug and is misfiring. The unburned fuel washes the oil film off the cylinder walls and reduces the sealing of the rings which will cause a compression test to show lower pressure than the other cylinders. Having 150 psi is not that bad and I think everything is probably fine -if the compression improves with a drop of oil this is probably what has happened especially if the engine is not burning oil. Also did you hold the throttle wide open during the compression test? This is important to get accurate readings.
Another reason for lower compression on one cylinder of a high miles engine can simply be carbon and varnish buildup in the piston ring lands causing the rings to stick and not fully seal. A good engine oil additive like Archoil 9100 that will slowly free up the rings may solve your problem and Archoil 9100 won't harm wet clutches. You must be careful with other types of really aggressive engine cleaners and desludging type additives as rapidly dissolving the varnish and carbon can also loosen up a lot of other accumulated stuff and possible plug oil passages. Do you run synthetic oil or petroleum based oil? Usually the carbon and varnish sticking of rings is more prevalent with high mileage engines running petroleum oils.

Thanks for all the detailed explanations. It's reassuring to know that 150psi isn't that bad. To answer some of your questions.
She doesn't burn any oil. Yes I held the throttle wide open during testing. I had been using 10w-40 semi synthetic oil. I just changed the oil and filter the other day . I decided to use 10w-40 fully synthetic this time, for the first time. As regards additives. I will give it a go. I realise, I will have to be careful with which one I use. I don't know if I can get archoil 9100 over here. I will have to go look. Something else came to mind now.
I synchronised the carbs last summer after I did the valve clearances. When I checked it again the other day. I had to re-adjust the offending cylinder . This might also shed some light on the situation.

Bmacleod · Apr 1, 2017

SMSW said:
I would doubt you could break off a piece of piston skirt and not have other, more severe problems. Besides, the OP mentioned the sound reoccurs - so unless he is experiencing ongoing piston skirt deterioration (a rather extraordinary situation) this is not the problem. If you lost a significant piece of the skirt, would not the piston rock a bit and score the heck out of the cylinder wall?

Actually, it is not uncommon to break a piece of a piston skirt off and the motor continues to run fine, except for a little more noise, which the OP alluded to an occasional noise while running. If a small piece were to break off, it could cause nothing more than a little cylinder scuffing and a slight decrease in compression over time, moreso because the rings wont seal properly on a piston that is "rocking" more than it should in the bore, but also because of excessive wear. Im not saying that is what the issue is, just that it is possible

sosdingle · Apr 1, 2017

Bmacleod said:
Actually, it is not uncommon to break a piece of a piston skirt off and the motor continues to run fine, except for a little more noise, which the OP alluded to an occasional noise while running. If a small piece were to break off, it could cause nothing more than a little cylinder scuffing and a slight decrease in compression over time, moreso because the rings wont seal properly on a piston that is "rocking" more than it should in the bore, but also because of excessive wear. Im not saying that is what the issue is, just that it is possible

Thank you for your input.
You make a very interesting point which I will bear in mind while investigating this issue.

SMSW · Apr 1, 2017

Bmacleod said:
Actually, it is not uncommon to break a piece of a piston skirt off and the motor continues to run fine, except for a little more noise, which the OP alluded to an occasional noise while running. If a small piece were to break off, it could cause nothing more than a little cylinder scuffing and a slight decrease in compression over time, moreso because the rings wont seal properly on a piston that is "rocking" more than it should in the bore, but also because of excessive wear. Im not saying that is what the issue is, just that it is possible

What do I know? I've only been inside three engines - hardly a statistical sample and really never delved all that deeply into what goes wrong with pistons and crankshafts - they have tended to be the most reliable part of the engine on cars and bikes that I've owned. This is interesting info to me - though I've seen pics of so called racing 'slipper' pistons - that more resemble a hockey puck than your standard piston with a skirt. On the other hand, race engines are often rebuilt after every race - stripped down to the last wrist pin, so what happens inside one of those engines is not applicable to a long lived block of aluminum like our ST engines.

sosdingle · Apr 2, 2017

I took the St out for a really good run today. Everything went well. No apparent problems. She seemed to be running fine. Return trip of around 100 miles with the intention of doing another compression test on that number one cyclinder afterwards. So I left it sit for about 20 minutes and then did the test. And to my surprise , it had read 150psi the other day, now it read 190psi. Now I must admit that when I did it the last day , I had just let it warm up in the shed for around 10 minutes. So was there a significant difference in temperature causing it to give a different reading? or has the teaspoon of oil test from the other day loosened a sticky ring, hence the good reading today. Surely , after today's run that little drop of oil has been well burnt out and is not responsible for the higher reading. Who knows. I will continue to monitor it in the coming days and weeks . Maybe all is well after all. I will keep you posted.

Uncle Phil · Apr 2, 2017

BTW, are you near the Dingle Pennsula? Just curious. From my 300,000+ miles of riding ST1100s, the best thing you can do with them is to ride them often. They can make some weird and unusual noises but if they run fine and the oil level is where it should be, I don't worry. ;-)

sosdingle · Apr 2, 2017

Uncle Phil said:
BTW, are you near the Dingle Pennsula? Just curious. From my 300,000+ miles of riding ST1100s, the best thing you can do with them is to ride them often. They can make some weird and unusual noises but if they run fine and the oil level is where it should be, I don't worry. ;-)

Hey Phil ,

Yes, I live on the Dingle Peninsula. I woul love to ride it more often , but the old weather here in the winter time wouldn't entice you to pull the bike out. From now on the weather will be improving. Today was a really nice dry, mild day . Ideal for motorcycling. Oil and coolant level stay where they should. So I guess I shouldn't worry either.

Uncle Phil · Apr 2, 2017

Here's from my adventure there -

http://www.unclephil.us/Ireland2010Day06.htm

It is a lovely place to ride and one of my favorite rides in Ireland (a lot fewer of those large buses than on the Rings of Kerry and Beara).
Two of my ST1100s have over 100,000 miles on them and they can make some 'strange' noises sometime.
My other one is approaching 90,000 miles and it does the same thing.
But I would not be scared to take off tomorrow on any one of the three across the country or up to Alaska.
I have found that the more I ride them and the less I work on them, the better they run!

sosdingle · Apr 2, 2017

Uncle Phil said:
Here's from my adventure there -

http://www.unclephil.us/Ireland2010Day06.htm

It is a lovely place to ride and one of my favorite rides in Ireland (a lot fewer of those large buses than on the Rings of Kerry and Beara).
Two of my ST1100s have over 100,000 miles on them and they can make some 'strange' noises sometime.
My other one is approaching 90,000 miles and it does the same thing.
But I would not be scared to take off tomorrow on any one of the three across the country or up to Alaska.
I have found that the more I ride them and the less I work on them, the better they run!

Its a small world after all. I've lived here all my life and get great enjoyment from riding these roads on a regular basis. I live about 2 miles from Dingle town , or village as you call it. So the Slea head drive and the Connor pass are a regular spin.
Glad to hear you enjoyed it too. You really got lucky with the weather. I enjoyed your description of your trip round these parts. You are obviously well travelled. My brother, brother in law and I have only got back into motorcycling again about 5 years since. The biking had to be put to one side while families were being reared. The wife's wouldn't have been too pleased if we were heading off and leaving them holding the baby so to speak. But anyway we are back in the saddle again and intend to do as much riding as we can. As regards the St, it's one hell of a bike. I've had many Honda cars and the reliability is second to none. I'm sure the St is the same. It's one of those bikes that you would feel confident about making it back home on , no matter how far off into the sunset you went. I enjoy working on anything that's mechanical and tend to be looking for problems ,where there may not be any.

Engine makes a crack like sound

sosdingle

dwalby

sosdingle

Bmacleod

Bmacleod

dwalby

saddletramp8511

R.I.P. - 2019/01/01

SMSW

bdalameda

PaleoCyclist

sosdingle

sosdingle

sosdingle

Bmacleod

sosdingle

SMSW

sosdingle

Uncle Phil

sosdingle

Uncle Phil

sosdingle