Low compression in front cylinder

[Rob_OS23]

Hey guys, long time no post!

Most may not remember me, others may remember me as the guy who bought a Vision about four years ago, who shows up here and there with a question or two, or to threaten the complete parting out of my V :)
Anyways, to update some that may not know, I have never in my heart given up on my Vision. I keep giving money to mechanics who rip me off. They fix all the easy stuff, and ignore the problem I have had since I bought it.
To recap, my bike runs like a top. Needs full choke to start, and is touchy until warmed up a bit, but once it's going, hold on for dear life!
The big problem has always been that it starts veerrryyy slooowwwlllyy. If it turned over any slower, it wouldn't start. It barely does as is, as it always has since I got it. Once it is warmed right up and shut down, it will hardly even turn over at all.
After forking out lot's of money I can't afford, i have still never seen any improvement. The good news, as some know, is that I now have a very professional and knowledgeable bike mechanic looking at it. At first, he was just supposed to find the problem. That was it. If he found it, and the bill would be out of my league, he would tell me.
He pored over the bike, and met his match. He really knows his stuff, and he has contacted many friends of his and can't find an answer.
The good news is that he has found a challenge he can't give up on. He is now donating his time to figuring it out. It does not make sense to him he says.
What he has found, so he says, is that the front cylinder only has about 80% compression.
He says that it starts so slowly because the rear cylinder is "dragging" the front cylinder along so to speak when I am trying to start it.
It has nothing to do with the starter itself.
He put another decent starter in it, and although it is a bit better, it is far from good.
The bike only has about 15000 KMs on it, so it should not be wear on the rings one would think. I don't know where he is at with it, I am planning on calling him tomorrow.
I was thinking about something, and feel free to smirk if you want at my absolute lack of knowledge here... ;D
I know nothing about how all this works, but one piece of information I forgot to give him is this...
When I bought this bike, one of the ends of the muffler was gone completely, rusted out. The pipes themselves were in great shape, but one had nothing at the end of it, just a hole.
I took it to a mechanic way back then, to have it safetied. These guys I found out after have a reputation for ripping people off.
Anyways, I can't remember how the discussion went, but I remember suggesting to them that they cut the other side out with a torch, and weld new baffles in both.
My guess is that they took baffles from an atv, because that is what my bike sounds like, and welded them in place.
For years I have always thought that the exhaust is just a trail of pipes that blow smoke from behind you. I have heard mention of back pressure over the years of trying to educate myself and all, as well as other things that have lead me to understand the exhaust is actually important..
This is where my possibly stupid question comes in...
Could having the wrong baffles there, or even just one affect the compression in the front cylinder?
It was, as I remember, the right hand pipe(from the back view) that had no baffle.
For all I know, they didn't even cut the other one out, maybe they just found one that looked a lot like the other, and welded it in there.
I feel embarrassed even asking this question, I have no knowledge of these things at all, hope I didn't come off to stupid.
What do you think?
If you have any suggestions, they'd be greatly appreciated.
These are supposed to be really strong engines, and he says that the weird thing is that usually, if anything, the rear cylinder goes first.
He is saying that in his opinion, if the front cylinder did not have such low compression, it would start fine. He has put some stuff in it it (liquid)that would loosen it it up if it could, with no affect at all.
We all know these things have problems, and it's been a while since I pored over the archives, but it seems that that I have a problem with the V that no one else has.
What could this be?
Rob

[QBS]

No time to go into your enquiery in depth.  But the condition the bikes exhaust system (or even if it didn't have an exhuast on it at all) can have zero effect on cylinder compression at cranking speeds.  Also, this concept of a low compression cylinder dragging down the normal compression cylinder and thus making the bike crank slowly sounds so wrong as to be incomprehensible.

[inanecathode]

Well. Slow cranking comes from one or more of the following:
Worn brushes, bad contact on the commutator
Oil soaked brushes, again bad contact on the commutator
Rusted in place brushes, almost no contact with the commutator
Bad connection from starter to starter wire
Chafed and thinned out starter wire
Bad connection from solenoid to starter wire
Bad connection from solenoid to battery wire
Bad connection from battery wire to battery
Low battery voltage

Theres not alot to the starting system on these bikes. If you have clean connections all through, good brushes and contact in the starter, and good voltage at the battery, it should crank over just fine. I'd be willing to bet your battery is probably pretty wheezed or the connections are dirty.
Your mechanic really needs to clean out the carbs. Poor starting is almost always dirty carbs and low battery voltage.

[Rick G]

Hi Rob , I don't care what this guys reputation is , He is at best  unknowledgeable, and at worst stupid.
Low compression on one cylinder will not "drag the other cylinder down"
Do you have a garage or shed that you can work in ? what part of the country are you in? we may have a knowledgeable member near you, to help you.
Almost all motorcyccle mechanics are ignorant, when it comes to the vision. Its not your average motorcycle.
Answer my questions and we can deceide how to proceed.

[Lucky]

Think about it:...
if anything an engine with low compression is going to spin faster from the starter, not slower. less pressure at TDC on the power stroke for the electric motor to overcome.

your mechanic is clueless... :(

[vadasz1]

Hi Rob , I don't care what this guys reputation is , He is at best  unknowledgeable, and at worst stupid.
Low compression on one cylinder will not "drag the other cylinder down"
Do you have a garage or shed that you can work in ? what part of the country are you in? we may have a knowledgeable member near you, to help you.
Almost all motorcyccle mechanics are ignorant, when it comes to the vision. Its not your average motorcycle.
Answer my questions and we can deceide how to proceed.

The most knowledgable member near you is.........wait............wait........................wait...............TIGER!!!!!!!!!!!!!

Give him a PM and let's see what the old guy can do.

[Walt_M.]

Ok, don't need to dis somebody's mechanic but... slow cranking can have many causes. First start with the easy stuff, is there sufficient voltage at the starter for cranking? Put a voltmeter on the input terminal of the starter, (+) on the terminal, (-) to the engine block or frame. Try cranking, you should have about 10V with the starter engaged. At least that is what I measured on mine about 30 min. ago after the bike had been sitting for 2 wks. And, yes it started, 2 yr old walmart battery and no charger. If the voltage is low, start looking for the cause. Another easy check, measure the voltage at the starter relay. There should not be a significant voltage difference(less than 1 volt) from one terminal to the other with the starter engaged.
If you have 10V at the starter and it is cranking slow, there is a problem with the starter. Most likely, there is oil in the starter due to a bad nose seal. Do not think that just because he said he replaced the starter that he really did or that the replacement starter was good.
Low compression on one cylinder on a low mileage bike that has been sitting a long time is probably due to stuck rings in that cylinder. They may eventually free up when/if you get it running. As for the mechanic saying the rear cylinder usually fails first, that is a generality about 60-70 yrs old based on the thought that the rear cylinder of an air-cooled V-twin does not get enough cooling air as it is blocked from the airstream by the front cylinder.
One last thing, dissing motorcycle mechanics should be limited only to the bad ones one knows personally. It is a pretty thankless job and I would not want it.

[jasonm.]

the slow cranking it likely oil soaked or worn brushes. Low compression in the front is MOST likely tight valves. This does happen. And proper adjustment is required. Using the proper tool makes it easier. Are you doing the compression test w/throttle open AS YOU SHOULD? to allow all the possible air in the cylinder...this is often forgotten. The smallest possibility is a bad head gasket.

[motorcyclezen]

My starter problems turned out to be bad simply loose connections. As for the mechanic, I'm going to have to go with Walt on that one and add that when I first got my bike, I went to 3 dealers hoping I could get them to do my carbs. Two refused and one Yamaha dealer said with would be $425 if I pulled the carbs, because Visions were such a pain and $675 if I left the bike. Most folks I think are afraid to work on the bike because: 1) it's old and 2) there are likely no replacement parts if something breaks and finally 3) repair manual supplies are limited. I ended up doing the job myself.

At least he's willing to try. I think it's a good idea to let your mechanic know that you appreciate his work and that there are resources available to help him sort through his difficulties viz. this website. I use it to spark interest at dealers when I go for parts. They often go out of the way to help me now.

Ed--

[YellowJacket!]

May just need a valve adjustment.

David

[Tiger]

 :) Rob, if I remember rightly throu' our many conversation's, you have a good spare motor sitting at your storage place. Have you, or you mechanic friend considered a swap out...iffin' that he believes it to be a compression problem... ??? Had you have been able to make it to the OnROV ride over this weekend, you would have been in an "ocean" of experienced Vision people...

I won't dis your mechanic because he has a thankless task in trying to work on a machine that even "qualified" Yamaha mechanic's couldn't figure out!!!...but your ROV family could ;)

              8).......TIGER....... 8)
       

[inanecathode]

You could also do a V drop test across the starting circuit. Put one end of the dvom on the positive battery terminal, and the other on the terminal of the starter. Crank it then, your voltage read out is how much voltage is bypassing the wiring between the starter and the battery. It should be no more than .5 volts. That is, lets say you're reading 6 volts. That means that theres enough resistance to block about 6 volts across the whole circuit. If you have that 6 volt reading (or whatever it is, anything above .5 or so i'd call bad) that means somewhere in the circuit theres a bad connection. If you leave one probe on the battery (or the starter) and work from that probe with the other probe all the way down to the other end of the circuit, somewhere along the line you'll go from .5 volts to 6 volts (or whatever you had measured). Between that point, and the previous point you tested, is where your bad connection is. Yes, its just that easy :)
You can do this test on your battery as well. Start the bike (or try to start it) and put one probe of your dvom on the battery terminal itself, and the other on the battery cable end. You're then measuring how much voltage isnt going from the terminal to the wire. Savvy?

[Rob_OS23]

I appreciate all the advice.
I am going to be calling him tomorrow. Maybe I heard him wrong or something about this whole compression thing...
He definitely knows what he's doing, I've heard nothing but good about him.
I would assume he has tried all these things, maybe not.
If he can't get it figured out soon, I will have to try it myself.
The weird thing is that I have had the starter looked at, and I was told that it is still in great shape, and I've never found any oil in it.
My battery was replaced last year, and has been well looked after. It is on that battery tender jr., or whatever it's called.
The carbs were hardly dirty at all, but I cleaned and rebuilt them with the keyster kit. The only thing I missed possibly is a spot I never knew about until someone told me a while ago. I was told there is a very narrow passage (in the hole where the emulsion tube goes)that needs to be cleaned out with thin wire, such as that found in a twist-tie. I was told this may help me with my choke, which seems very touchy, and has to be left full on, and adjusted slightly a few times while the bike warms up some.
The valves have never been checked that I know of, although you would think someone would have in the times I have had it in shops.
The electrical connections and such have never been checked by me, but again, you would think that this would be one of the first things that a mechanic would check.
I guess I'm just glad to have found someone who cares and wants to help.
I know you guys all do too, but everyone is so far away. I'll let this guy try a little more. He is working for free after all :)
I'd gladly pay to have it fixed, already tried that route though. If he does figure it out, I will be giving him something, unless he flat out turns it down.
I plan on getting it back soon one way or another, and if it's not fixed, I'll ask for detailed instructions on what I need to do to check these things some of you mentioned. 

[QBS]

I sense a lot of assumptions on your part regarding what you think should have been done to your bike.  You might want to try and verify some specifics.

[Walt_M.]

Yeah, I hate to be a 3rd person in trying to diagnose a problem. I know what SHOULD be tried but I don't know what really has been tried so I am giving up on this one.