Cam chain tensioner dying - Honda CBR250R Forum : Honda CBR 250 Forums
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post #1 of 18 Old 09-22-2016, 04:02 PM Thread Starter
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Cam chain tensioner dying

So over the past few weeks, my bike developed a strange, intermittent symptom. When stopped at a light, I could feel a "knocking" in my handlebars. This did not happen every time I stopped, and seemed random. I have a Leo Vince Corsa exhaust, which is quite loud, making it difficult to listen for any engine noises specific to the motor. It also didn't help that whenever I reached my destination and stopped to put my ear to the motor, the noise was gone. The bike had approximately 28,300 miles on the odo (~48,000km).

It's hard to describe the noise; but the feeling was almost like bearing knock, or when you lug the engine, just more subdued. Of course, I tried simple things first: make sure it wasn't noise from the brakes floating (no brakes applied), or clutch noise (same in neutral). Nothing alleviated the random noise. Being as paranoid as I am, I changed the oil and noticed nothing out of the ordinary (metal shavings, etc), but the noise did not improve. Next on the list was the dreaded cam chain tensioner. It seemed my symptoms were identical to someone else's on here that described it as a "ticking felt in the handlebars". So I decided to check the action of the tensioner to make sure it operated properly.

After removing the tensioner from the bike (had to get the clutch cable out of the way to have room), everything checked out. The spring extended the plunger when released, and the worm gear retracted the plunger when turned. All of the strength in my hands could not push the plunger back in when extended, meaning it was still supposedly locking itself in position and not backing off through engine vibrations and such.

As such, I cleaned the tensioner, fully retracted and released the plunger a few times to make sure the action wasn't binding, locked it in place, and re-installed on the bike. I then released the plunger and heard/felt it extend inside the crankcase. Much to my dismay, the noise is still present and has not improved, so I have ordered a new tensioner which should be here Saturday.

I will post results of the new tensioner, which is an OEM Honda automatic tensioner (horror stories about the manual ones; too paranoid). I do hope this fixes the problem, as most videos/descriptions you hear about these failed CCT's sound absolutely horrible, like metal slapping metal continuously. This was never that pronounced, but you could definitely tell something was off and it was doing something it had never done in 5+ years.

If the new tensioner does fix the problem, hopefully this will help others with the same symptoms catch theirs early, well before it gets to this point: https://youtu.be/KJVqwzrsJfg?t=1m15s

P.S. This guy has another video about how the tensioner works, and how to retract and lock the plunger without Honda's special tool.
Seems this is VERY prevalent on CRF250L's.

Seems those that simply have worn/broken springs, as long as the retraction mechanism is working properly and keeping the plunger from backing out, you could simply turn the mechanism counter clockwise in small increments to take up the slack. But I'd rather just replace it.

Tis better to be thought a fool and remain silent, than to open one's mouth and remove all doubt.
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post #2 of 18 Old 09-22-2016, 04:27 PM
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I've got a manual CCT on my CRF150 and another on my son's Ninja 250.

Not a bad solution as long as you stay on top of the adjustment and don't crank 'er down. In general I think the auto ones apply too much pressure, at least in the Ninja's case. When you make an adjustment on the CRF at idle you can hear the engine slowdown if you get too much tension, and that's turning the bolt with your fingers.
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post #3 of 18 Old 09-22-2016, 04:57 PM Thread Starter
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Quote:
Originally Posted by jkv357 View Post
I've got a manual CCT on my CRF150 and another on my son's Ninja 250.

Not a bad solution as long as you stay on top of the adjustment and don't crank 'er down. In general I think the auto ones apply too much pressure, at least in the Ninja's case. When you make an adjustment on the CRF at idle you can hear the engine slowdown if you get too much tension, and that's turning the bolt with your fingers.
Yep, I had indeed considered that route. The only thing (besides having to adjust it, and worrying if I have it too tight) I have against them is the bolt is no longer a sealed system like the pan head hex bolt on the stock unit. I've heard some have a bit of oil weeping out around the threads of the lock nut/bolt.

Any weepage from yours jkv? Which brand did you go with?

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post #4 of 18 Old 09-22-2016, 05:12 PM
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Quote:
Originally Posted by cbrlocal View Post
Yep, I had indeed considered that route. The only thing (besides having to adjust it, and worrying if I have it too tight) I have against them is the bolt is no longer a sealed system like the pan head hex bolt on the stock unit. I've heard some have a bit of oil weeping out around the threads of the lock nut/bolt.

Any weepage from yours jkv? Which brand did you go with?
No oil from the Ninja's that I've seen. We have had that one for quite a while on 2 different bikes. My son bought it, and I'm not sure of the brand. APE is a quality manufacturer of custom performance parts, and that's the brand it could be.

The one for the CRF hasn't been on long, and there weren't many choices. I got it off of eBay, and it wasn't a company I had heard of. Fairly simple piece to make, and it seems to be working fine.
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post #5 of 18 Old 09-26-2016, 11:58 AM Thread Starter
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Small update:

New tensioner installed, and I've idled the bike. Ticking was there for a few seconds, then disappeared. Hopefully was just taking up the slack. Haven't been able to ride yet due to weather and needing to haul things for work in my car. I will update after I can do a typical work commute when I noticed the ticking/knock (likely Wednesday).

I will say that upon removing the original tensioner for the 2nd time, again everything checked out with the mechanism and gave no indication that it would be faulty. The tensioner had spring pressure throughout the plunger travel and did not back off with pressure. My theory is the spring has lost tension over time, or as it moves further out in plunger travel, doesn't have as enough spring pressure to keep the noise down.

I do however think I have found the source of the noise we all hear when the tensioner craps the bed: After removing the factory tensioner, I stuck my little finger in the hole in the block to feel the cam chain guide. With no tension on the guide, I could wiggle it laterally side-to-side. That side-to-side movement replicated the ticking/rattle exactly (of course with much lower frequency than with the engine running). I do hope my guide is fine, as I assume it is; otherwise, I anticipate the noise wouldn't have been intermittent and would have been horrendous.

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post #6 of 18 Old 09-28-2016, 11:03 AM Thread Starter
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No ticks today with the new tensioner; although, it did sometimes go a whole day without acting up on me before, so still not sold completely. All seems well thus far!

Tis better to be thought a fool and remain silent, than to open one's mouth and remove all doubt.
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post #7 of 18 Old 09-28-2016, 06:05 PM
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but wait,, is 'not doing anything'
a symptom - that we should
be worrying about...

[just kidding mate,
excellent feedback
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post #8 of 18 Old 09-28-2016, 11:53 PM Thread Starter
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Quote:
Originally Posted by shisoshin View Post
but wait,, is 'not doing anything'
a symptom - that we should
be worrying about...

[just kidding mate,
excellent feedback
Only if "not doing anything" is because it's not getting ridden!

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post #9 of 18 Old 10-03-2016, 03:02 PM Thread Starter
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No more ticking. Bike feels great.

Still have no explanation, as my old tensioner when taken out passed every functional test I could throw at it. My only guess was the tension spring was just not strong enough to push the plunger out any farther against the residual force of the chain. The worm gear never backed off after extension, so likely it just wasn't able to extend any farther on its own. Turning counterclockwise a smidge would likely have fixed this problem, even with the original tensioner. But, who knows when the worm gear mechanism would fail.....
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post #10 of 18 Old 01-26-2017, 10:35 AM Thread Starter
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UPDATE:

Ticking is back with the new tensioner. I thought I was hearing and feeling the tick slightly earlier this week, but couldn't be entirely sure. The ride into work today confirmed it; may have to take the plunge and go with a manual tensioner, as two factory ones have passed all mechanical working tests, but are obviously not doing their jobs.

This new replacement tensioner didn't even make it 1000 miles.

I'm going to attempt to manually tighten this one slightly and see if the noise disappears, as these auto tensioners have internal worm gears to keep them from backing off. As long as that is working, I should be able to adjust it to remove the slack without it loosening up again.

Tis better to be thought a fool and remain silent, than to open one's mouth and remove all doubt.
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