Bent valve or bad timing?

[mbtaylor01]

Hey everyone,
My cam chain slipped a tooth when I was changing out my cam tensioner :spank: Totally my fault, I'm so frustrated.

My bike still has a stable idle, but now at about 100 rpm less than usual. It sounds a lot deeper and less smooth at idle and at all rpm ranges (it kind of sounds like it's growling).
It revs normally, but when the rpms come down the engine seems to pause/stumble for a split second.

I have three questions:
1) If all of the valve clearances are within spec, is that a guarantee that the valves aren't bent?

2) If I do a compression test and none of the cylinders have 0 compression, is that also a guarantee?

3) Given how my bike now runs, how likely is it that only the timing is messed up, and not the valves? Thanks guys

 

[TownsendsFJR1300]

Double check- re-set the timing chain so you know it's dead nuts on.

While you have the valve cover off, checking clearances, do a "LEAK DOWN TEST". (Much easier with the valve cover off).. You'll need a small compressor (100PSI) and the tool.

If your not familiar with it, to do the leak down test you bring that ONE cylinder to TDC (compression stroke) and lock up the crankshaft(right side).

Hook up the tool into that cylinder and pump in 100 PSI. If a valve is bent, it will show a low reading on the tool and you'll hear air coming out either the exhaust or intake.

A leak at the intake would indicate a bent intake valve, same for the exhaust. You will know EXACTLY what valves are bent.

A bent valve would have a now LARGER CLEARANCE as it's NOT closing fully..

Side note, the same set up, if you heard air coming from the crankcase, (oil filler hole), your rings / piston would be faulty- air passing INTO THE CRANKCASE..

**The FJR (same set up) will run a tooth off but a noticeable change in power.. I suspect, your valves are probably ok, but best to check so you don't burn a valve that's partially bent/open and make things worse...

This is the tool I use, about $60.00:

 

[mbtaylor01]

Ok, an update. I took the valve cover off and measured the valve clearances -- all within spec. When turning the crankshaft I'm feeling compression. So we're good there.

The timing is off, but only by a millimeter (I measured it). It's off by about how thick the timing marks on the cam wheels are. There's no way that could affect anything, right?

Some pictures when mark on crank wheel is aligned:




When I turn the crank so that the two cam wheels are perfectly aligned, the crank looks like this:


I know a leak down test would probably be the best thing to do, but I'm trying to hold off on that as a pancake compressor and a leak down tester would set me back around $170.

If the timing is an issue, I don't know how to fix that because going forward or back a tooth would probably put it way off. Advice?

 

[TownsendsFJR1300]

The first pic, it's hard to see the mark. (The rest look fine). I assume the first pic / mark is just a knats hair below the head?

Other than that your marks look good to me! If you moved any one tooth, it'd be WAAAY off...

With the valves within spec, that pretty much verifies nothings bent and leaking.

The Leak down test at this point would be nice and would give you the "how healthy your internals to your engine are", but I suspect your good.

If your CCT wasn't keeping the chain tight, NOW the new one is and timing should be steadier (and a slight change wouldn't surprise me).

What do have the idle set to (normal running temp)?

If you upload a video (with GOOD AUDIO), would be helpful.

BTW, you should be safe to ride it with where the marks are now...


* When I swapped to Iridium's, I had to adjust the idle (up as I re-call), with NO other changes..

 

[mbtaylor01]

Yeah, the mark is flush with the head.

Funny you should mention iridium plugs! After changing the CCT and hearing how differently my bike ran, I swapped the stock plugs for iridium (on the off chance that something would happen). The bike sounded exactly the same after, so I guess I just forgot about it. Definitely could explain why my bike idles a little lower than usual. I'll post audio once everything's put back together.

Is there a best idle speed? Usually my bike ran at about 1600-1700 rpm cold and about 1200-1300 warm. It now runs the same cold but 1100 rpm warm.

BUT my bike sounded rough before and after the new plugs. Hmmmm. Clearances ok, timing ok, bike doesn't run/sound like normal after changing CCT. Very strange.

There's a local mobile motorcycle mechanic who's supposed to be good. I'll see if he'll come out and do a leak down test for a reasonable price.

 

[TownsendsFJR1300]

I think your fine but I would like to hear an audio..

You can take it for a ride, if the timings off(and it does NOT appear to be), the engine will perform very differently.

I have my warm idle set at 1,100 exactly, on purpose. At 1,300, I get some vib's thru the mirrors, the engine just sounds too high,
and more importantly, it doesn't clunk into first gear nearly as bad (the gear box is spinning lower). (Pull in the clutch a little sooner if in neutral)

I've had the idle set there the entire time I've owned it, no issues. If your new at riding, you may want to leave it high (stock) just so you don't stall or until you get used to it..

Now my cold idle isn't as high as yours but it's generally warmer down here. I don't think there's an adjustment for the cold idle RPM's but the coolant, as it warms, lowers the idle. Make sure the coolant is in very good condition.

Being that deep and the bikes still apart, it won't take your guy 1/2 hour to check with the Leak Down tester. That tool has saved me a bunch of time trying to get an engine running right..

Lastly, fresh fuel is critical. Two products I run in every gas engine I own. Yamaha's RingFree is a fuel system and top end cleaner. A quart is about $50 but treats 320 gallons.

I repair small engines (mostly carb related) and once running, their tuned (high speed with a portable tach). They sit overnight (to make sure cold start is good). I'll often re-tune the carb and get ANOTHER (up to) 2,000 RPM's (Echo and Stihl chain saws mostly) often. That's W/O doing anything else but letting the RingFree do it's thing.

I use either "Gas Shok" or "K-100" as a fuel stabilizer as well in every gas machine I own / work on. I've had fuel (ethanol) last as long as TWO YEARS (boat with a large tank). I avoid Stabil (long story, but IME, junk).

A Shock treatment (RingFree) 2 oz / one gallon of fuel will very likely smooth out the engine operation.

https://www.shopyamaha.com/product/details/ring-free-plus?b=Search&d=34&nw=yamaha-motor-company


Page not found – USA Fuel Service

| Kinetic Fuel Treatment (I use this in the boat)

 

[mbtaylor01]

I went ahead and bit the bullet, got the leak down tester you suggested and a pancake compressor. Valves are perfect!!! 1-2% leakage on all of them, measured each one three times just to make sure.

I'm at work right now, totally swamped this week but I recorded about ten seconds of audio before going to work. Please let me know if the quality isn't good enough, regardless I will upload a longer video in a few days when my schedule isn't so rough.

[video=youtube_share;wiKG_hoqvtE]https://youtu.be/wiKG_hoqvtE[/video]

 

[mbtaylor01]

Dang, I zoomed in on the odometer, not very helpful. Meant to change it to tachometer. Will correct soon.

 

[TownsendsFJR1300]

Excellent, sounds good too..

Now you know for certain everythings on the money and that engines top end is VERY TIGHT and in great shape...