motor question

[itroop]

Hey all. Without going into a lot of detail, I have a question for you guys. The dealer is going to replace the "short block" of my motor. They say they will re-use the cylinder and pistons since they are well within specs. The problem they found was a scored crank. The motor was stumbling and they found one cylinder had a lower compression than the other. Should this cure the problem? What do they mean by replacing the short block?

 

Thanks

[4wheeldog]

In automotive terms, a short block is the engine minus heads, intake, exhaust, starter, oil pan etc.

That said, a scored crank would not account for low compression.......This would be caused by a valve, ring or piston problem. It could also be caused by a bad camshaft. Since you have a scored crank, if this is a warranty situation, they really should replace the whole motor, IMHO. The only way to score a crank in one of these motors is to run it without sufficient oil. All kinds of damage will then occur. Good Luck!

[Stan Walker]

itroop

 

You asked about this a little over a week ago. I suspect you will get exactly the same answers now as then. The symptoms you describe do NOT fit the fix you tell us they are doing.

 

I suspect you are NOT relaying the information accurately. Have you ever played the old party game where one person whispers a story to the next person who whispers it to another and so on until the story has passed through 8 or 10 people. Usually by then you can't even recognize any part of the original story. Well that's what I think is happening here. The wrench tells the salesman who tells you who tells us and the result doesn't make any sense whatsoever.

 

To put it another way. A scored crank will NOT cause one cylinder to have low compression. No way. No how. Low compression is caused by bad parts in the part of the engine you say they are keeping. Why would they keep the bad parts?

 

Stan

[itroop]

itroop

 

You asked about this a little over a week ago. I suspect you will get exactly the same answers now as then. The symptoms you describe do NOT fit the fix you tell us they are doing.

 

I suspect you are NOT relaying the information accurately. Have you ever played the old party game where one person whispers a story to the next person who whispers it to another and so on until the story has passed through 8 or 10 people. Usually by then you can't even recognize any part of the original story. Well that's what I think is happening here. The wrench tells the salesman who tells you who tells us and the result doesn't make any sense whatsoever.

 

To put it another way. A scored crank will NOT cause one cylinder to have low compression. No way. No how. Low compression is caused by bad parts in the part of the engine you say they are keeping. Why would they keep the bad parts?

 

Stan

Stan. You're right. I did ask this question recently. I guess I just wanted to be sure, getting this information from a forum off the internet. I did ask the service guy that's, in charge of my bike, if you will, if the scored crank would cause the low compression in one of the cylinders. He assured me that it would. He also told me that they had tested all the other parts that are not going to be replaced and assured me they were well within specs. I was hoping for a new motor, but the warranty company authorized only the short block. Any suggestions on how to deal with the dealer working on my bike? This has juust become a royal pain in the ass. Any help would really be appreciated.

Thanks

[Stan Walker]

If I were you.......

 

I would print out your post and the answers you receive and show them to the mechanic working on your bike and ask him to help you explain this problem and fix to us.

 

If I were you.......

 

I would search around on the web and find a tutorial on how internal combustion engines work. It's useful to truly comprehend what the mechanics of this world tell you. It's also fun to be able to 'talk shop' with other owners about problems, fixes, improvements, design screw-ups, etc. If maybe what sets the BMW crowd apart from other bike groups. Many of us are deep into the nuts and bolts, not just the riding, but the design too.

 

If I were you.......

 

And once upon a time I was.

 

Stan

[ShovelStrokeEd]

What Stan said.

[Big D]

And once upon a time I was.

Well said.

 

D

[itroop]

Stan,

Well I took your advice. I printed out the responses I received on the forum and did a little reading on the internet on combustion engines. Now I was ready, all this info in hand and called the dealer working on the bike.

 

First I talked with the mechanic who last touched my bike. He was straight up with me and didn't try and beat around the bush on anything I asked him. That was good. This was his response. He told me that this particular bike had a history of the problems previously mentioned. I bought the bike last year. The previous owner apparrently had the same issues with the bike. Just before I bought it, the top end had been rebuilt. The compression problem had been an issue with the previous owner, something I had just found out from the mechanic. So, everything had been replaced on the top. He was up front and told me that he wasn't exactly sure what was causing the lower compression, but since everything on the top was new, they were going to replace the bottom end. With that said, they are also re-honing the cylinder, sending everthing out to have de-carboned and basically he said, the motor would essentially be new when it was put back together. I asked about a new motor. He told me the warranty company was pushing for him to rebuild the crank and we were lucky to be getting the short block. I told him my concern, what all of you mentioned, the crank couldn't possibly be the cause of low compression. He told me that it was possible the crank could be the cause of the low compression. He said that if the crank was scored badly enough, the connecting rods would be different in length therefore one rod not working correctly. He then referred me to the service manager.

 

I spoke with him and he told me that definately, the crank, without a doubt could cause the low compression in one side, citing the same cause as the mechanic. He then added that with a scored crank, the main bearing journal would be off, I guess(sorry, can't remember the terminology), and the rod wouldn't pushed to where it was supposed to go. He said that with a rod not working right, more air, not compreessed air, would be allowed in the cylinder, and I'm sorry, I forgot the rest. But he said there was a direct corrolation with the scored crank and the low compression. He also told me that I was lucky to be getting a short block instead of a rebuild.

 

I'm supposed to get my bike back on the 11th. I guess I'll just have to wait and see what happens.

 

Thanks for giving me the advice I needed to approach these guys. I'm sure it didn't help you wrenches any, but if I learn more, I'll pass it along.

 

Mark

[4wheeldog]

Sorry, but they fed you a truck load of horse hockey. The only answer they gave you that has anything to do with reality is......They don't know.

If indeed the top end is in good shape.......Pistons, rings and valves......Then the problem almost has to be the cams. I doubt that those are included in the short block. Ask them to verify that the cams are free of any signs of wear, and have them at least miked.....(Measured with a micrometer) to verify that they are not "Flat".

Again, a scored crank virtually requires that the motor be run without oil. The cams will generally be ruined before the crank under these circumstances. JMHO. Good Luck!

[jackflash]

Really gives me confidence in my new BMW. Arrogant fking Germans. I think you're getting jerked around by BMW.

[4wheeldog]

Really gives me confidence in my new BMW. Arrogant fking Germans. I think you're getting jerked around by BMW.

To put this in perspective, this problem is on a used bike of undetermined history.....The problem is being addressed by extended coverage insurance, not BMW. Anybody can ruin any bike by running it without oil.......All you have to do is forget to fill it, after you drain it!

[Stan Walker]

He said that if the crank was scored badly enough

 

That would be one hell of a scored crank to lower the compression that way. I suspect you could hear that motor coming about a mile away it would be knocking so badly.

 

Still, you gave it your best shot for extracting information from the dealership. And there is hope that the re-honing of the cylinders will solve the compression problem.

 

Good luck, let us know how it turns out.

 

Stan

[EdinLA44]

Hopefully there will be some sort of warranty on their work. Have them do a compression check on it when it's all back together (which they should do anyway) and make sure they write down the pressures. Once you get it back, ride it a couple thousand miles and check the compression again and then keep checking it periodically for awhile.

[itroop]

Well thanks to all that replied. I hope that you guys are wrong and the service dept. is correct. I wanna ride my beamer. I just hope that replacing the short block will cure the problem. If not, I don't know what the heck I'll do, short of getting rid of the bike, which I don't want to do.

 

Anyway, thatnks for all the input. I'll keep you posted when I get the bike back.

 

Mark

[Cali Kid]

Mark, I'm curious. Has the cylinder ever been replaced? You said a top end had beeen done. That could include piston and cylinder or not. And again you state that they are reusing the cylinder after honing. I would suggest that there might be a problem with the with the cylinder. It might be indicated by high oil consumption. what has your's been like? Does the plug in that bad cylinder look different than the good one.

[itroop]

Mark, I'm curious. Has the cylinder ever been replaced? You said a top end had beeen done. That could include piston and cylinder or not. And again you state that they are reusing the cylinder after honing. I would suggest that there might be a problem with the with the cylinder. It might be indicated by high oil consumption. what has your's been like? Does the plug in that bad cylinder look different than the good one.

 

Hi Rick,

I was told that everything in the top end had been replaced. I should mention that everyone in the Pac NW that has anything to do with BMW bikes has had their hand on it one time or another. Satisfying, huh? My oil consumption has been normal, compared to my other bikes. You know, my bike has been in and out of the shop so many times that I really never got the opportunity to check the plugs.

 

Thanks for the input to all. And I will keep you posted.

Mark