Topic: CB350F camchain tensioning

[Evel E.]

Hello,

My CB350F has what sounds like a pretty rattly camchain.  I just tried adjusting at it.  I'm reading the instructions in the Honda factory manual for the CB350F and CB400F that I found online and the Clymer manual that I've bought.

Iit appears that I should see an adjuster bolt and a lock nut on the front of the engine, just above the oil filter housing.  However, I do not!  I see a hole here.  What's really odd is that I don't see traces of any threads in the hole.  If I did have threads in this hole, it doesn't look like there's anything there for the bolt to push or pull.  The bottom of it is concave and looks like it's shaped into the aluminum cylinder wall.  I don't see anything that looks like a steel tensioner or anything.  It's dark outside, but I'm looking at it with a pretty good light.

-Eric

[Evel E.]

Well from:

http://sohc4.us/?q=node/161

There is no external tensioner adjustment for the cam-chain, and that may be a
mistake: our test bike had a subdued clatter at idle that by sound and location strongly

However, the manual that I downloaded says that:

All information, illustrations and specifications contained herin are based on the 1972 model CB350F, which is what I have. 

On page 11, it shows the ajuster bolt and locknet sticking out just above the oil filter, where I have a hole with no internal threads or anything.

Did they add a camchain tension adjuster at some point halfway through 1972 CB350F production?

Hello,

My CB350F has what sounds like a pretty rattly camchain.  I just tried adjusting at it.  I'm reading the instructions in the Honda factory manual for the CB350F and CB400F that I found online and the Clymer manual that I've bought.

Iit appears that I should see an adjuster bolt and a lock nut on the front of the engine, just above the oil filter housing.  However, I do not!  I see a hole here.  What's really odd is that I don't see traces of any threads in the hole.  If I did have threads in this hole, it doesn't look like there's anything there for the bolt to push or pull.  The bottom of it is concave and looks like it's shaped into the aluminum cylinder wall.  I don't see anything that looks like a steel tensioner or anything.  It's dark outside, but I'm looking at it with a pretty good light.

-Eric

[keiths]

Mine was manufactured 11/72 and it has the adjustment bolt.

[Evel E.]

Mine was made in 5/72.  I want to look at this hole closer when it gets light, but I don't see any remnents of threads inside it.  Even if it stripped out I'd expect to see something.

-Eric

Mine was manufactured 11/72 and it has the adjustment bolt.

[Terry in Australia]

They ALL had a trick "Horse shoe" tensioner that wrapped around the crank and was adjusted by a bolt/locknut arrangement on the front of the engine. It was quite common for "ham fisted" owners to strip the cast in thread, or break the bolt, thus rendering the tensioner useless.

Don't run the engine until you fix this, apart from the untensioned chain slapping around the inside of the engine gouging aluminum and dumping the "swarf" into your oil supply, there's a good chance your camchain will "jump" a couple of teeth on your cam and send your valve timing out, shoving valves into piston crowns and if that happens, you'll cry yourself to sleep. Cheers, Terry.

[Evel E.]

Hello,

How does the adjuster work?  I've cleaned out the hole and had a pretty good look at it in the light.  I can't make out any remnents of threads in the aluminum at all.  The bottom of the hole just ends in the aluminum cylinder block.  Nothing attaches on the bottom or sides either.  I can't see the top side of the hole, the oil filter housing blocks my view.  There's another, downward pointing bolt on the lug where this blind hole is, do you know what this does?

-Eric

They ALL had a trick "Horse shoe" tensioner that wrapped around the crank and was adjusted by a bolt/locknut arrangement on the front of the engine. It was quite common for "ham fisted" owners to strip the cast in thread, or break the bolt, thus rendering the tensioner useless.

Don't run the engine until you fix this, apart from the untensioned chain slapping around the inside of the engine gouging aluminum and dumping the "swarf" into your oil supply, there's a good chance your camchain will "jump" a couple of teeth on your cam and send your valve timing out, shoving valves into piston crowns and if that happens, you'll cry yourself to sleep. Cheers, Terry.

[Gordon]

Here's a picture from one of my books that gives a pretty clear view of the workings of the tensioner.  There should be one hole above the filter housing pointing downward at about a 45 deg. angle that the tensioner rod fits in.  There should be another hole just below this one pointing upward at a right angle to the tensioner rod.  That one is for the lock bolt that holds the tensioner rod in place when it's screwed in tight. 

[Trevor from Warragul]

A picture speaks a 1000 words.  I'd say the thread has been comprehensively stripped!  Mine has been too, which is why I have a non-standard allen bolt fitted...

[Jay B]

Mine's got the tension bolt, looks to be original. So what's the procedure for tightening?

[Evel E.]

I found a copy of the picture of the tensioner arrangment in the Honda manual too.  There are a couple springs under the downward bolt that actually apply the tention to the horseshoe via the push bar.  So the bolt that goes in more or less parallel to the oil filter locks the push bar in place to whatever the tension works out to be when the engine is idling at 1200 rpm.  This is the way that my manuals say the adjust the tension.  However, shouldn't I see the pushbar at the bottom of the hole?  Is the pushbar steel or aluminum.  It looks to me like it just bottoms out in the block.  The hole is shaped like the attached picture.

A picture speaks a 1000 words.  I'd say the thread has been comprehensively stripped!  Mine has been too, which is why I have a non-standard allen bolt fitted...

[Bodi]

Some PO ruining it is much more likely than Honda making the engine without an adjuster. The article was probably written by a journalist who expected the tensioner to be behind the cylinders like on just about every other OHC bike engine, and who didn't bother to look at the manual.
The adjuster rod is about 6 or 8mm diameter with a machined flat where the locking bolt hits.You can see the tip of it (with a mirror) if you remove the upper bolt, but it does not come out that way; the spring retains it.
You might be able to fix it by drilling the hole and tapping for a larger bolt or installing a time-sert rethreading insert... but probably you should split the cases and do it properly - avoiding jamming the rod with swarf will be hard, and through tapping for a larger bolt pretty unlikely with the rod in place. A time-sert could be done from the outside if the hole is deep enough, I'd want to do a very thorough cleaning to get any crap out after the drilling and tapping!

[Evel E.]

Is the pushbar too big to come out of the hole where the upper bolt goes?  It looks like you could take out the upper bolt, the two springs (with a small magnet) and then the pushbar.  Do you know if the pushbar is steel or aluminum?

If the hole is completely stripped and the locking bolt is missing.  I'm worried that the original lockbolt must have indented the pushbar which is why the hole appears to bottom out in the engine block.  See my revised attached picture.  If it was overtightened like this I'd imagine that the pushbar is probably bent and frozen in position and wouldn't move. 

From the picture in the Honda manual,, it appears that the pushbar pushes down on the horseshow.  Pushing down on the horseshoe would appear that the it would straighten out the curvature of the tensionsers which would reduce the tension on the chain.  Is that how it works?

Some PO ruining it is much more likely than Honda making the engine without an adjuster. The article was probably written by a journalist who expected the tensioner to be behind the cylinders like on just about every other OHC bike engine, and who didn't bother to look at the manual.
The adjuster rod is about 6 or 8mm diameter with a machined flat where the locking bolt hits.You can see the tip of it (with a mirror) if you remove the upper bolt, but it does not come out that way; the spring retains it.
You might be able to fix it by drilling the hole and tapping for a larger bolt or installing a time-sert rethreading insert... but probably you should split the cases and do it properly - avoiding jamming the rod with swarf will be hard, and through tapping for a larger bolt pretty unlikely with the rod in place. A time-sert could be done from the outside if the hole is deep enough, I'd want to do a very thorough cleaning to get any crap out after the drilling and tapping!

[Bodi]

"Is the pushbar too big to come out of the hole where the upper bolt goes?  It looks like you could take out the upper bolt, the two springs (with a small magnet) and then the pushbar.  Do you know if the pushbar is steel or aluminum?"

It doesn't come out that way, the spring is a larger diameter than the bolt hole. Why the bolt is even there, I don't know. The pushbar is steel.

"If the hole is completely stripped and the locking bolt is missing.  I'm worried that the original lockbolt must have indented the pushbar which is why the hole appears to bottom out in the engine block.  See my revised attached picture.  If it was overtightened like this I'd imagine that the pushbar is probably bent and frozen in position and wouldn't move. "

Hard to diagnose from here
Possibly the bolt sheard off and someone tried to drill it out and gave up, or drilled into the rod. I think you'd see signs of the rod if it went that deep though. And steel should have rusted by now...

"From the picture in the Honda manual,, it appears that the pushbar pushes down on the horseshow.  Pushing down on the horseshoe would appear that the it would straighten out the curvature of the tensionsers which would reduce the tension on the chain.  Is that how it works?"

You push the front of the horseshoe down rotating the whole thing around the bottom pivot mount , forcing the rear to go up making the rear tensioner leaf to bend and tension the chain. Camchains are always tensioned on the "slack" side which is the back on all Honda transverse OHC bike engines as far as I know.