Bent connecting rod?

You have a fuel problem in #4. Bad injector most likely. Take it out and get it tested. Could also be a stuck open start valve. Don't know what the VFR has for that.

 

Thanks - I'll read up on the injector diagnosis procedure. This may save me from troubleshooting the same problem on the replacement engine [If the replacement engine turns out to be necessary].

Compression on #3 cylinder is 190psi.

There will be a momentary pause for standard mechanical snafu...I torqued the M10 plug adaptor tightly onto the end of the rigid extension that the compression gauge attaches to. I used a closed end wrench to tighten the plug adaptor. The adaptor still stayed down in the plug hole and the rigid extension unthreaded from the plug adaptor - the plug adaptor must have snugged down against metal instead of onto its oring. I'm going to go get some fresh red loctite to get the extension bonded to the plug adaptor, let it cure, then pray I'm able to remove the plug adaptor. I can't see using an easy-out if the red loctite fails, there's too much chance of metal shavings from an easy-out dropping into the cylinder.

I saw another compression test kit with a rigid extension that had a rubber cone adaptor instead of a threaded plug insert.

Does anyone know if the rubber cone insert type compression tester fittings provide accurate readings? I'd prefer not to be doing so much praying that the threaded plug insert comes back out with the extension at each cylinder test [If the plug adaptor comes out at all - it would be ironic if a compression test led to removing the head to get the tool out].

 

A standard starter valve synch would show whether it had a stuck valve (but the bike has to be running first...).

If the injectors check out, then you might have a problem with the fuel pressure regulator, specifically if the diaphragm has a tear, that would allow fuel to pass straight into the vacuum line...which maybe goes to cylinder #4 and would give a sooty plug.

I also highly doubt that VFR that was running suddenly gets a bent rod. As stated, a hydro-locked cylinder might result in that, but that can't happen in a running engine. My vote is for a fuel supply related issue.

 

Thanks Cadbury64. The bent rod does seem highly unlikely. I'll proceed with recommended fuel system diagnosis steps, once I get the compression test plug adapter out.

 

NEVER crank down on anything you screw in to a plug hole. You just found out why.

 

So true. I hope that's today's only big lesson. It didn't seem that cranked; I felt the oring squish a little and then clunk against metal. That was more than enough. The plug well is juuuust a little too tight for the 11/16 socket that fits the adapter to get into, so red loctite, do your stuff.

I've gotta keep an eye on autospell - she's always changing loctite to lactate.

 

Rubber cone type compression tester probably won't fit down the plug hole..........unless you remove the cam cover (very easy except finessing it out of the frame !) which would also give you better access to remove the stuck part.

 

Speaking of Avatars...

I'm afraid I saw your Avatar laying on the middle of the highway in Northern California recently. Sorry to be the one to have to break the news!

 

Knight will be lactating (milking) the thread attributing the glitch to electrical problems, his neighbors, the economy , the weather and maybe even, THE AVATAR..

Cratered a old Triumph 500 engine once. It threw a rod. Best I recall there was a total loss in power and one hell of a lot of bad vibrations. A bent rod on a V4 engine if the engine was running would do much the same.

 

Thanks Badbilly - I've been out of town for work all week, but return to the garage tomorrow to see if the now-cured red loctite will get the compression test adapter out. I also checked with mechanic I know and like about coaching me through fuel system analysis because of the blackened business end of one plug while the other three were like new.

 

Good luck! Had me VFR for 25 years and have not heard of a thrown or bent rod in all that time. I think most will be interested to see what you find.

 

Update - red loctite worked - compression test adapter came out easily. Here are the results of the compression test:
#1 - 175 psi
#2 - 175
#3 - 190
#4 - 200

#4 is the one with the blackened plug - not significant buildup, but discolored black where the other three plugs look new.

The previous owner said the mechanic he took it to diagnosed #3 as having a bent rod.

I very carefully measured piston travel distance on each cylinder by inserting a slim rod into the plug hole until it touched the piston, marking the rod at bottom dead center and at TDC then using digital calipers to measure the difference. I got these readings:
#1 46.25mm
#2 46.99mm
#3 47.56mm
#4 47.85mm

Next step - fuel system troubleshooting. Find out why the plug in #4 is fouled.
Question - if the problem is ignition - not getting spark, the plug wouldn't foul, would it?

 

Is the plug sooty black or oily black? Sooty black is too much fuel not enough air. Think of it as leaving the choke on too long in a carbureted bike. I would assume it's sooty black and there is some carbon build up on the piston, hence the slightly higher compression. Does the cylinder have spark? Forgive me if you've already said so, I'm too lazy to go back and look.

Sent from my XT1575 using Tapatalk

 

Could be as simple as a bad plug. You said they look new, but I would try a set anyways if it was my bike.
5th gens have an 8k change interval, and 6th gens are at 12k.

 

Thanks for the replies. I just checked it and the plug is sooty; the blackening is 'dusty' and easily rubs off the rim of the plug with my thumb not pressing at all.

Correction - the blackened plug is #2 based on the label I put on it at removal and not relying on my aged brain.

It seems next step is putting the three good plugs back with a new #2 plug to eliminate the plug as a possible cause, then verifying spark, then beginning a fueling/injection troubleshoot.

 

This sounds familiar. Ive heard of similar symptoms on Honda 919s and F4Is.

Check your fuel pressure regulator.

 

Thanks Sniper - fuel pressure regulator goes to the top of the fuel system checklist.

Does it seem logical to confirm spark first? Or does the leftover burnt soot mean it is firing and I don't need to check spark?

 

I'd check the FPR first.

Good luck. I'm keeping an eye on this thread.

 

I stopped by a few*stores [Auto- as well as non-auto stores]*to purchase or assemble a precise piston-depth gauge. I was using my fork oil height measuring tool as a template; a slim straight metal tube or rod with a solid collar that can be fixed in place by a threaded setscrew. With a smaller collar than my fork oil tool's collar*that would sit on top of the VFR's valve cover plug opening, the plan was to slide the tube or rod down to the piston at BDC, fix the collar with the setscrew, extract the rod and fixed collar, then use calipers to measure piston depth. Rinse and repeat for TDC. Compare piston depths between cylinders.

Toward the end of my research a helpful Oreilly Autoparts fellow heard me describe a fundamental condition of my project that I had failed to pay attention to: with all sparkplugs out,*when I turn the crankshaft with a wrench through the timing port, the engine generates significant friction/resistance at various points around the rotation. My helpful fellow held the opinion that the engine should have even resistance/friction throughout the crankshaft's rotation when it's not making compression. His opinion is that a small four-cylinder engine is built so tightly - thin*webbing,*crankshaft journal spacing, and tolerances in general*-*that the very noticeable changes*in resistance throughout the crankshaft rotation indicate that some large rotating part or parts are bent inside the cases.

To attempt to identify where in each*revolution the resistance increased, I switched from a ratchet to a rigid wrench and began to turn from the bottom - call it 6 o'clock. For two revolutions, the stiction occurred*just before*6 and again just before 12 o'clock and lasted 20-30 degrees of rotation*at each location. As I continued to turn the wrench without removing it from the timing crankshaft bolt, the sticky spots migrated*in a vague clockwise procession [7ish and 1ish, then 8ish and 2ish, etc.].*I couldn't pin the change down to an exact pattern. Since I did the compression test with the battery and starter, I believe the oil pump has already moved some of the new*oil into the lubrication system.

Question - does the uneven crankshaft resistance indicate seriously unhappy major rotating/reciprocating components?

Thought 1 - if it's NOT*definitely done-bended-real-fersher bad, I'll drain oil, remove clutch and stator, and check the crank turning resistance without those two potential drags on the system. Then proceed with the FPR, injector, and other troubleshooting.

Thought 2 - if it IS*done-bended-real-fersher bad, I'll drain oil and coolant, remove engine, and install the replacement engine I purchased before I began to scratch my head about this*"bent*rod" engine.

 

After I finished the previous post I realized the painfully obvious...valve spring resistance.