Author Topic: CB400F Cam Chain Adjustment Bolt (Read 14246 times)

Ernest T · « **on:** February 28, 2011, 04:58:02 PM »

Well, my bolt is long gone and the threaded hole it goes into is mangled with the remains of the broken off bolt. I'm going to have to take drastic measures and think I'll be installing a time cert. I need to know if I can do this in the frame or not. I need to drill an oversize hole, tap it, and screw in the time cert. I've been looking at pictures on the site and realize that I can't see inside the case with the head and cylinder off so that's not going to work. Is there any chance I can take off the pan and remove the chain tensioner from that end or do I have to split the cases?

camelman · « **Reply #1 on:** February 28, 2011, 07:28:52 PM »

You have to split the cases to pull the tensioner and repair correctly. That requires the engine being out of the frame.

You could get by in the meantime by screwing in the closest standard thread bolt. There should be enough material left to create threads. I did that a while back out of necessity. I don't remember which size I used, but it worked fine until I had a chance to pull the engine apart. Work the bolt back and forth slowly when you "cut" the new threads. I don't recommend using a tap. Taps are tapered, so you'll only get a few threads cut before the tapered end bottoms out in the hole. If you aren't super careful, then you'll tear out those two new threads you just cut.

The correct repair, as you stated, is to timesert it.

Camelman

malcolmgb · « **Reply #2 on:** March 01, 2011, 06:55:32 AM »

Quote

I don't recommend using a tap. Taps are tapered, so you'll only get a few threads cut before the tapered end bottoms out in the hole.

there are 3 types of tap, the first 2 taper the last is called a bottoming or plug tap, it is parallel to the end and allows threading to the end of a blind hole.

Ernest T · « **Reply #3 on:** March 02, 2011, 06:17:17 PM »

What does the case look like where the adjustment bolt enters? Is it recessed or flat? Also, does the o-ring go on the 8 or 10 mm portion of the bolt?

Joel · « **Reply #4 on:** March 02, 2011, 07:11:59 PM »

I had this same problem except I'm the one that sheared the bolt off in the hole. I was able to remove the broken piece with a drill, an extractor, a small butane torch and some time. The hole is a metric thread and a standard fastener will work.

Ernest T · « **Reply #5 on:** November 21, 2011, 04:48:52 PM »

After a long delay I'm finall working on the bike. I have the front wheel off to replace the fork seals so I took a good look at the cam adjuster. I am going to drill out the bolt and see if I can tap the hole for a new one. I'm also going to pull the pan and see if I can't run some solvent through the hole and out the bottom of the engine. Even if some shavings get into the bottom of the sump, they shouldn't get through the pickup screen or filter.

I'm going to get the cam adjuster working, then adjust the valves and sync the carbs to see if I can't get the engine to run quieter. Wish me luck.

bollingball · « **Reply #6 on:** November 21, 2011, 05:39:42 PM »

Use a bottom tap and put grease on it that will trap most of the metal.

donpark1086 · « **Reply #7 on:** November 21, 2011, 06:03:07 PM »

If you have an air source, put a reasonably strong stream of air into the crankcase and blow the chips from the tap out of the hole being tapped. Fit a cork with a tube into the oil filler oil. Maybe close off the crankcase ventilation system. But don't over-pressurize and blow seals or cause the engine to rotate with pressure under the pistons.

Ernest T · « **Reply #8 on:** November 24, 2011, 12:52:28 PM »

Once I took the front end off I could see up into the cam tensioner bolt hole and me and the PO made a mess of it. He got started off center and the drill bit slipped off the broken bolt. I came along behind and made it a real mess. I'm going to have to replace the engine case to get it working right.

Luckily I've got another engine. It's in bad shape except the cases and the cam tensioner hole is perfect. I bought the whole bike for $100. I think it was a low mileage bike that was involved in a front end collision. The gas tank had a crease in it from the forks. All the good parts had been stripped off and it sat outside for many years. I'm in the process of taking it apart. The cam journals look brand new, but everything below the head is rusted. The pistons are frozen in their bores and the crank is rustedtight. Amazingly, the stator ohms out in specs.

I've never replaced half a case on a engine with plain bearings. Can you replace one half or do they have to be replacedin pairs?

Mugger_Mike · « **Reply #9 on:** November 24, 2011, 08:09:42 PM »

Quote from: malcolmgb on March 01, 2011, 06:55:32 AM

Quote
I don't recommend using a tap. Taps are tapered, so you'll only get a few threads cut before the tapered end bottoms out in the hole.

there are 3 types of tap, the first 2 taper the last is called a bottoming or plug tap, it is parallel to the end and allows threading to the end of a blind hole.

Well yeah three basic types the bottoming would be used to finish the hole here is a link to a pretty cool chart I recntly found

http://www.newmantools.com/taps/styles.htm

It's a tap guide, styles, chamfers etc.

grcamna2 · « **Reply #10 on:** November 24, 2011, 09:03:57 PM »

Quote from: Ernest T on November 24, 2011, 12:52:28 PM

Once I took the front end off I could see up into the cam tensioner bolt hole and me and the PO made a mess of it. He got started off center and the drill bit slipped off the broken bolt. I came along behind and made it a real mess. I'm going to have to replace the engine case to get it working right.

Luckily I've got another engine. It's in bad shape except the cases and the cam tensioner hole is perfect. I bought the whole bike for $100. I think it was a low mileage bike that was involved in a front end collision. The gas tank had a crease in it from the forks. All the good parts had been stripped off and it sat outside for many years. I'm in the process of taking it apart. The cam journals look brand new, but everything below the head is rusted. The pistons are frozen in their bores and the crank is rustedtight. Amazingly, the stator ohms out in specs.

I've never replaced half a case on a engine with plain bearings. Can you replace one half or do they have to be replacedin pairs?

I think you have to replace both halves of the crankcase as a set...but check your other sources to be sure.

camelman · « **Reply #11 on:** November 24, 2011, 09:34:22 PM »

After reading through this again, I'm n ot quite sure which bolt is bad. Is it the upper bolt or the lower bolt? Did you extract the broken bolt?

Instead of going to the trouble of putting that original bolt back in there, I'd suggest trying this. Find another bolt the same thread as the upper bolt. Grind off the first six threads of that bolt and install a nut on the threaded shaft. Screw the bolt into the upper hole by hand until you feel it contact. Snug the nut down without turning the bolt. Then, start the engine and let it warm up enough to idel smoothly. Once it is idling smoothly, tighten down that upper bolt until the chain noise goes away. You shouldn't have to tighten it much (probably less than a turn).

The snugged nut on the bolt will keep the bolt from loosening, but will allow you to adjust the bolt when needed. I've done this on two engines now (one 350F and one 400F), and it has worked perfectly.

Camelman

bryanj · « **Reply #12 on:** November 24, 2011, 10:07:51 PM »

NO YOU CAN'T change half a case they are machined as pairs

HondanutRider · « **Reply #13 on:** November 25, 2011, 05:00:09 AM »

What Camelman describes applies to the upper blanking bolt (i.e. replacing it) and assumes that the lower locking bolt is what has been damaged. Doing this modification should prevent the cam chain adjusting mechanism from loosening any further and should "hold" it at the correct adjusted tension without the need for the lower locking bolt to be functioning.

Ernest T · « **Reply #14 on:** November 25, 2011, 08:01:18 AM »

Quote from: bryanj on November 24, 2011, 10:07:51 PM

NO YOU CAN'T change half a case they are machined as pairs

That's what I was afraid of, I was hoping I could just pop the top half off and replace it. Luckily, both halves look pretty good. Thanks.

Ernest T · « **Reply #15 on:** November 25, 2011, 08:11:26 AM »

Quote from: camelman on November 24, 2011, 09:34:22 PM

After reading through this again, I'm n ot quite sure which bolt is bad. Is it the upper bolt or the lower bolt? Did you extract the broken bolt?

Instead of going to the trouble of putting that original bolt back in there, I'd suggest trying this. Find another bolt the same thread as the upper bolt. Grind off the first six threads of that bolt and install a nut on the threaded shaft. Screw the bolt into the upper hole by hand until you feel it contact. Snug the nut down without turning the bolt. Then, start the engine and let it warm up enough to idel smoothly. Once it is idling smoothly, tighten down that upper bolt until the chain noise goes away. You shouldn't have to tighten it much (probably less than a turn).

The snugged nut on the bolt will keep the bolt from loosening, but will allow you to adjust the bolt when needed. I've done this on two engines now (one 350F and one 400F), and it has worked perfectly.

Camelman

Thanks fo the response. Its the bolt that stops the tensioner from moving that is broken off. Apparently its putting pressure on the shaft because I can't move the tensioner with a screwdriver stuck down the hole the blanking bolt covers. Either that or the pivot is damaged and the tensioner is frozen. I'm still messing with it and if I can get the tensioner to move it sounds like your solution will make it functional. Thanks.

strynboen · « **Reply #16 on:** November 25, 2011, 08:55:57 AM »

have some pics..from my engine..you cant see the cam chain or tensioner..from bottom of engine..i have drillet mine bolt aut..but faund more problems in gearbox..so have splitted it total now..

strynboen · « **Reply #17 on:** November 25, 2011, 09:15:43 AM »

Ernest T · « **Reply #18 on:** November 25, 2011, 03:49:01 PM »

I took my spare engine apart this afternoon. Once I used big enough hammer to get the cylinder off it went pretty quickly. I thought about trying to save it, but the sleeves had deep pits in them so I wasn't gentle with it. It sat outside with no pipes, carbs or sparkplugs for a long time

From the top, it looks pretty good.

But once you move past the head, its rusty.

But there's not much wear on the cam chain guide and slipper.

One of the pistons looked okay, It's the one on the right.

But the other three looked like this. The top ring is packed solid with something brown.

I followed the disassembly instruction in the Clymer manual, but ran into a problem with the primary chain and cam tensioner horseshoe. The primary chain was connected to the bottom half and the horseshoe was connected to the top half. I managed to slip a socket between the halves and removed the two bolts holding the horseshoe to the top half. The good news is all the cam adjuster parts are in good shape.

Following the procedure in the Clymer manual, I pulled the main shaft out the side, but the primary sprocket wouldn't come out. What's the secret to getting it out?

Ernest T · « **Reply #19 on:** November 25, 2011, 04:48:54 PM »

I finally drilled out the broken bolt in the good engine and there is no cam adjustment bar in the tunnel, Something must have happened to the horseshoe and its dropped into tne sump.

camelman · « **Reply #20 on:** November 26, 2011, 12:03:05 AM »

@ Hondanutrider, thanks for that explanation. I should have included that in my statement.

@ Ernest T, that engine looks a little rusty. If I was at home right now, then I'd offer some parts of my spare 350F engine. I won't have access to that engine until I'm back in the State in January though. Let me know if you have trouble finding replacement parts for the rusty bits. It looks like the starter clutch and the kickstart assembly are coated in rust. You might be able to clean them with an oily rag (that rust wipes off easily sometime. I would also flush all the oil passages to make sure you don't have rust/crud sitting in them that could go to the crank bearings.

You won't feel much motion of the adjuster when you push down through the blanking plug hole. You will feel a pulsing with the engine at idle, and it is not likely that you will be able to push hard enough to make that pulsing go away. If your horseshoe is eaten up at all, then you can try dressing it with a finishing file to remove burrs (I did that once out of desperation and it worked). As long as that horseshoe can move, it will do its job. I realize your engine isn't working right now, so you'll have to wait until you have it back together to understand what I'm talking about. By the way, while you have it apart, do/check the following:

1) replace all the bottom end gaskets. You can buy kits for abotu $35 and there is nothing work than a lower end oil leak after you have reassembled, reinstalled, filled with fresh oil and started the bike.
2) replace your valve guide seals
3) check if first gear is loose on the shaft. If it is, then check back in and someone on here will tell you how to repair it. It should be a cheap and easy repair and will only require having a new bushing turned to replace the stock bushing that is worn.

Good luck,
Camelman

Ernest T · « **Reply #21 on:** November 26, 2011, 10:10:55 AM »

Quote from: camelman on November 26, 2011, 12:03:05 AM

@ Hondanutrider, thanks for that explanation. I should have included that in my statement.

@ Ernest T, that engine looks a little rusty. If I was at home right now, then I'd offer some parts of my spare 350F engine. I won't have access to that engine until I'm back in the State in January though. Let me know if you have trouble finding replacement parts for the rusty bits. It looks like the starter clutch and the kickstart assembly are coated in rust. You might be able to clean them with an oily rag (that rust wipes off easily sometime. I would also flush all the oil passages to make sure you don't have rust/crud sitting in them that could go to the crank bearings.

You won't feel much motion of the adjuster when you push down through the blanking plug hole. You will feel a pulsing with the engine at idle, and it is not likely that you will be able to push hard enough to make that pulsing go away. If your horseshoe is eaten up at all, then you can try dressing it with a finishing file to remove burrs (I did that once out of desperation and it worked). As long as that horseshoe can move, it will do its job. I realize your engine isn't working right now, so you'll have to wait until you have it back together to understand what I'm talking about. By the way, while you have it apart, do/check the following:

1) replace all the bottom end gaskets. You can buy kits for abotu $35 and there is nothing work than a lower end oil leak after you have reassembled, reinstalled, filled with fresh oil and started the bike.
2) replace your valve guide seals
3) check if first gear is loose on the shaft. If it is, then check back in and someone on here will tell you how to repair it. It should be a cheap and easy repair and will only require having a new bushing turned to replace the stock bushing that is worn.

Good luck,
Camelman

The engine in the pictures was one I got out of the breakers for the cases, its not the engine out of my bike. This one sat outside for a lot of years without carbs or pipes and loose spark plugs.

The engine in my bike was running good, it just made a lot of top end noise. I saw the broken cam tensioner bolt and figured it would be a simple matter of removing the broken bolt and adjusting the chain, but unfortunately it was a lot more than that.

Since I'm swapping cases, I'm going to do a total rebuild from the bottom up--new gaskets, seals, main and rod bearings (if required), valve job and new primary and cam chain.

camelman · « **Reply #22 on:** November 26, 2011, 11:36:49 AM »

It sounds like you have a good plan there. Something else to check that could cause that top end noise is if the valve cover was ever disassembled and reassembled with the rocker springs on the wrong side. If you have a hanyes or shop manual available, then find a picture of where the springs are supposed to be and compare it to yours. If the springs are on the wrong side, then you'll get a lot of noise and accelerated wear. I found this out the hard way recently. It was a big pain in the butt.

Your crank bearings are probably fine. You might want to replace the piston rings though, but only after measuring the bores. As an alternative, I really recommend the 466 kit off eBay. $150 or so shipped, and you should be able to get the block bored for $200 or so. It is a completely different engine. If you rering, then you are looking at some cash for the parts and honing costs. At that point, it isn't much more money to step up to the 466. It will put a big smile on your face!!!!!!!

Camelman

Ernest T · « **Reply #23 on:** November 26, 2011, 02:34:20 PM »

Here's where I am today, the cases are apart and I'm cleaning them up.

I'm wondering if I should put the crank from the original engine into the cases from the spare engine or just use the crank and cases from the spare engine. On the plus side I know where I'm starting from, the mains are labeled BABBB on the spare engine, but the shells show some wear. I took measurements, but my micrometer only measures to thousands of an inch, and the chart in the manual is labeled in ten thousandths. The crank journals measured 1.259" and I need to know if it is between 1.2590 and 1.2594" or 1.2594 and 1.2998".

Here's what the bearing shells look like

They show some wear so I'm assuming they should be replaced. I'm going to spend the next few weeks collecting gaskets and seals and misc parts while I decide what to do.

bryanj · « **Reply #24 on:** November 27, 2011, 10:38:11 PM »

Those shells are damaged by dirty oil/crud and do need replacement, forget the measuring you need to use plastigauge to get it 100%

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Author Topic: CB400F Cam Chain Adjustment Bolt (Read 14246 times)

bollingball