Compression loss

[norcal]

I need some advice on an engine problem. My bike is a 2005 FJR with 29,000 miles. For about 5,000 mi there has been a lack of power or hesitation below 1,800 rpm-no big deal. then a few thousand miles ago on start up, once the idle droped from 2,000 rpm to 1,500, the idle would drop fairly fast to 600 or 700 rpm and stall if I wasn't there to give it throttle. The bike ran fine once warmed up and didn't lack power after 1,800 rpm.

I did the valve check at 26,000 and things were fine. It ran fine for another 3,000 mi. , then one morning it wouldn't start. I tried to diagnos the low rpm problem, but no fault codes were registered in the fault code memory.

I've done all the required mainteance and have considerable experience working on engines.

Getting to the point, I hauled it to the dealer and left it. The mechanic couldn't start it either. He did a compression test and all four were about 125 psi, and should be +/- 200 psi. Then he did a leakdown test and those values were about 70 % of what they should have been. He thinks when I did the valve check I let the timeing chain slip a tooth on the crankshaft sprocket. I seriouly doubt that, first because it ran fine for another 3,000 mi with no performance decrease, and second there has to be a lot of slack in the cam chain for it to clear the tooth tips on the sprocket.

Here's the question: if it jumped a tooth, that would be a 9 deg change in the valve timeing, would the bike still run, and wouldn't there be a noticeable differance in the performance?

I did notice a buzzing about 3,500 rpm from the engine or perhaps a peice of plastic in the last few thousand miles, though the bike doesn't use oil. If the valve guides were worn could that cause enough wear on the valve seating areas to cause the low compression problem? I have no reason to suspect it of being a ticker (the mechanic hasn't heard of this problem), except that I'm trying to explain the problem.

Thanks, Jim

 

[Capt. Bob]

Bumped this up in case any of the REAL piston heads missed it.

Good luck Jim.

 

[v65]

1)So if a leakdown test was performed, what's leaking? That's the point to doing this test, to identify the problem area.

2)Have you had the TPS recall done?

3)At 125 psi it should still run if everything else is fine. As you say the skipped tooth is crap, the bike was running.

BTW, I am not a REAL piston head, but I play one on the internet.

 

[ionbeam]

I've gotta Gunny what V65 said. If they did a leak down test there is almost zero effort to find what was leaking. Remove the oil fill cap -- place ear over opening -- listen -- hear lots of air, it's rings, pistons or cylinders. Place ear at air box -- listen -- hear lots of air, it's intake valves. Place ear over exhaust pipe exit hole -- listen -- hear lots of air it's exhaust valves. Remove radiator cap -- bubbles -- blown cylinder head gasket or cracked cylinder head.

Another way to check the valve timing is to align the mechanical timing marks and check to see if Cyl #1 is at top-dead-center. You can use a very high tech tool to watch the piston move up and down in the bore -- a full length trusty ol' #2 yellow pencil. If the piston is not at TDC when the marks are aligned then the mechanical timing is wrong.

If all the cylinders were low by the same amount I would believe that valve timing should be the first thing checked. Depending if the valve timing is advanced or retarded could make the difference between a simple fix and burned exhaust valves and possibly a damaged cylinder head. Steadily degrading performance would happen if the exhaust valves were burning...

IMO, leaking valve stem seals and worn guides will not produce equal leak-down rates. There has been a report of a stray piece of carbon holding valves open, but it would be improbable that it would happen to all cylinders and that they all leaked the same amount.

You need to revisit the cylinder leak-down test, and good luck!

 

[radman]

There have been several cases IIRC of stuck rings on these. A decarbonizing agent has fixed them. Don't recall if the owners "babied" them to death or not. A slipped chain on a cam gear would cause more compression loss than you're seeing I think-as well as other damage, though it could move on one cam only and perhaps not destroy the valve train. But a tooth on the crank would definitely show up as a no start, or have real running problems, as both cams would be retarded significantly. No codes just means everybody's checking in with acceptable numbers-mechanical failure won't set a code unless it affects sensor output. The buzzing is interesting-but again no codes means the cylinder ID sensor didn't get whacked. Check my math, but with 38 teeth on the cam gears, that means 19 teeth on the crank, which translates to a 19 degree change with a slipped chain at the crank, a major change which makes me doubt the engine would run at all. With the cam tensioner problems that have surfaced on some motors, and you're description of the symptoms, plus no codes, that's where I would be looking.

 

[3dogs]

I would connect a vacuum gauge to the intake manifold. You could "T" it into where the MAP sensor is. Even if the engine won't start you can watch the needle with the starter motor turing to measure cranking vacuum. The needle should show steady pulses (one for each cylinder as it goes through its intake stroke) indicating that all cylinders are sealing the same. Also, if you get no cranking vacuum the cam timing is off (assuming there is no intake manifold or vaccum hose leaks).

You never mentioned if when checking the valves at 26k you adjusted any of them? I'm assuming that you did change some shims otherwise there would be no reason that the cam timing is off. Is that correct?

 

[norcal]

Thanks for all the replies and suggestions. The ratio of cam gear to crank gear teeth is 2 to 1 of course, so if the chain slipped one tooth on the crank sprocket that would be about a 9 deg shift on the cam timing (1/2 of 360 deg divded by 19) Please correct me if I have this wrong. I would think a 9 deg shift in cam timing would be a very noticable diference in performance, which didn't happen. I don't have the experience to know for sure.

I did change a couple of intake valve shims, they were below specs. I loosened the cam bearing caps, pivoted the cams over enough to get the buckets out, and made sure the chain didn't come off the cam sprockets.

There were differences in the compression piston to piston, and the leak down numbers also. It was a couple of phone calls with the mechanic and I didn't write them down and he didn't recall the exact numbers.

could be stuck rings, but wouldn't the oil consumption increase? I don't know what's going on, but am wondering if the valve guides are worn could that cause the valvle seating to deteriorate enough to affect the compression.

Jim

 

[radman]

Yup. In any case, 9 degrees (at the cam, 19 at crank) is a huge number in cam timing, and would certainly affect operation. Stuck rings wear rapidly, but mostly have the effect of overly scraping oil off the walls-and the oil is the real seal in the engine. The carbon expands when heated, forcing the rings against the walls as well as preventing their circular movement from crosshatch, and also preventing the ring from reacting to chamber pressure, which is a sealing action. That's why you put oil in during a compression test, to seal the rings and see if valves are the culprit. With a decent crankcase venting system, you don't really see the blowby effect, because the intake system burns the fumes, noticeable oil loss only occurs when it's really gotten bad. I suspect, still, screwed up valve timing as the culprit, likely caused by a junk tensioner, which was marginal and then quit completely, as others have had. Sloppy cam timing could raise all sorts of hell.

Edit-keep in mind the cylinder id sensor depends on the cam timing to trigger injection-could explain the no start, as the engine requires that sensor to be right on to work, won't set a code because the sensor is fine, just improper signal.

 

[v65]

You reported degrading performance over the last 3k miles, skipping a tooth on the timing chain would not be degrading but quite sudden I would think. If you had installed the cams incorrectly this should have appeared immediately, unless you like Ionbeams burning valves theory. What am I missing?

 

[ionbeam]

There were differences in the compression piston to piston, and the leak down numbers also.

That is actually a good thing; cam timing would affect everything fairly uniformly.

Reluctance to idle with low idle speed, low power at lower rpms and starting problems are often symptoms of vacuum problems. How does (did) the vacuum levels look at each cylinder? Is there a chance that there is damage to the rubber boots that connect the fuel rail to the cylinder head? Are the clamp bands snug?

Do you know if the low compression & leak % match up with the cylinders whose valves were re-shimmed?

If you suspect sticking rings, go to the cylinder(s) with low compression and put a small amount of engine oil into the combustion chamber and check the compression again. The oil will temporarily help the rings to seal and compression will go up.

Well, these are a few more logs for the fire...

 

[norcal]

good ideas, thanks. I'll ask the mechanic to look at the chain tensioner befor taking the head off, that could explain the sudden non-starting problem, though why it started fine up to the point it quit is beyond me.

I synched the throttle bodies about 3,000 miles ago, after the low speed problem was happening. I had been getting a consistant 210 to 220 mm of mercury, then at 26 k miles and at 29.3 k all i could get was 160 mm, so definetly less vacuum at the throttle bodies. Looked around for an air box leak or disconnected vacuum hose, but found nothing. All the exhaust valve clearances were 8 or 9 thou at 26 k mi.

Don't know about the low compreesion figures matching up with the valves I adjusted, didn't get the numbers from the mechanic. He told me every Yamaha sevice school he's been to told him to set the intake valves at 4 to 7 thou. I mentioned the book said 6 to 8 and he stuck to 4 to 7 being right. All 8 intakes were 3.5 to 5.5 thou. I bumped the 3.5 valves up to 5.5.

It's a mystery, I'll share what I find.

Jim

 

[norcal]

I saw the head off the bike at the shop a few days ago, and the reason for the loss of compression was a suprise to say the least. It was the oil I've been using, Shell Rotella T 15-40 wt. The air box sides of the throttle body butterflies were coated with about 1/16 th of an inch of soot, which could be scraped off with a fingernail. Apparently as the oil heated it gave of vapors that via the crankcase breather entered the intake air. This coated the butterflies and created enough carbon in the head to keep a few exhaust valves from closing completely. The 2 valves that were out of the head had small pits on the seating lands.

I feel a little foolish for having used this oil, which will turn out to be avery expensive choice. Talking to the mechanic before seeing the head, he asked me what oil I was using, because of the smell when he took tha valve cover off. He asked me it the container said suitable for motorcycles, which is not the case.

Jim

 

[radman]

I call BS. That much oil vapor shouldn't be present to begin with-regardless of brand, excessive blow-by will do the deed quite well. Many here have run the Rotella for many miles and have not had this issue-possible an overfill occurred in the bikes past? Air filter torn, or being bypassed? Many causes for this-the least likely of which has been offered.

 

[Checkswrecks]

+1 to Rad.

Had the bike been on it's side, allowing a passage to get plugged?

 

[Constant Mesh]

If the carbon was due to oily fumes from the intake system the intake valves would also likely be affected. But you said the problem was found at the exhaust valves only.

More likely you are experiencing excessive oil coming down the exhaust valve stems/valve guides and being burned near the exhaust valves.

I've seen photos of the TB butterfly valves from one or more FJR's on this forum and a residue or dark coating could be clearly seen. So it may be common to all or many bikes with lots of hours of operation.

You could disconnect two hoses at the airbox and see how much oily residue is present.

The crankcase breather hose brings the oily fumes into the airbox. The air induction system hose carrys filtered air/oily fumes to the reed valves in the engine head assembly.

Also you could remove the air filter and reach in and touch the air intake nozzles and check for excessive oily residue.

 

[norcal]

Some interesting ideas. Excessive blowby would be worn rings, when the new exhaust valves are in and the compression is rechecked we'll see about that.

The bike was dropped an its side about 4,000 miles ago because of the low speed power problem, my fault of course. What passage would have been blocked by that?

The valve guides are in good condition, and at 29,000 miles it didn't burn any noticeable amount of oil. the intake valves are getting washed with a fuel air mixture, so they wouldn't get as much carbon as the exhausts.

I'm unsure about the exact cause, maybe something else will surface after the bike is back together. I am sure of the repair cost of $1,500, new exhaust valves included.

The air induction system is something I'm going to find out more about via the manual, could be a problem there caused the excess carbon.

Jim

 

[norcal]

My bike is back together, and I've ridden it to Colorado from Cal and it runs great.

After reassembly the compression was around 190 psi per cylinder so the rings are good, as they should be with only 29k miles. The problem was the use of Shell Rotella oil for about 27k miles. As I mentioned earlier the throttle butterflies were coated with soot on the back sides (from the crakcase breather hose), and enough carbon collected in the head that the exhaust valves weren't closing completely. The exhaust valves had small deposits of carbon spots on the mating surfaces. The valves weren't ruined but being that far into it the best course was to put in new exh. valves.

I'll be using motorcycle specific oil from now on, not something made for deisel trucks.

 

[radman]

How then would you explain all the guys running non-specific motorcycle oil (including lots of Rotella users) and yet this is the first alleged problem traced to it's use I can recall, ever?

 

[03silverbullet]

My bike is back together, and I've ridden it to Colorado from Cal and it runs great.After reassembly the compression was around 190 psi per cylinder so the rings are good, as they should be with only 29k miles. The problem was the use of Shell Rotella oil for about 27k miles. As I mentioned earlier the throttle butterflies were coated with soot on the back sides (from the crakcase breather hose), and enough carbon collected in the head that the exhaust valves weren't closing completely. The exhaust valves had small deposits of carbon spots on the mating surfaces. The valves weren't ruined but being that far into it the best course was to put in new exh. valves.

I'll be using motorcycle specific oil from now on, not something made for deisel trucks.

At 158,000 miles, I have had no problem with Shell Rotella oil.

The oil was not your problem.