CB200 Camshaft Modification to prevent wear/seizing

[bsnodgre]

DoTheTonners-

I must say this is my first cafe racer project, and my first post, and this forum has been incredibly helpful. The knowledge on here never ceases to amaze me.

Anyway, about finished with my 1975 CB200T and took it out a couple times (the build is documented here: https://www.facebook.com/media/set/?set=a.10101761250322168.3176743.13720370&type=1&l=1303cd67f2). It ran/rode great...until the piston seized, or so I thought. Tore into the engine last week and found that the head, valves, pistons, rings, and cylinders are all in remarkably good shape. Turns out the left side of the cam didn't get enough oil, and has, over many a mile, worn down the aluminum cam journal to the point that it finally became one piece. After a few hours, hammers, and heat, I got the cam housing off the end of the cam:

After some research here and on a couple other forums, it looks like this is a somewhat common problem on the CB200 (maybe 175s too?). I finally found a used cam in good shape, but I'm hoping to prevent this happening in in the future. Oil flow on the CB200 is from the crank, up through one head bolt, and then pressurizes the cam, from right to left. There are tiny holes through the cam to let oil out to lubricate, for example on each lube.

My question is, would it lower the system pressure in the cam too much if I drilled the hole in the left side a bit bigger to make sure the cam and cam journal are sufficiently lubricated? (indicated by the orange circle and question mark in the above picture) Any major concerns I should keep in mind if/when I do this? Anyone found a good, long-term fix for this?




Thanks!

 

[acm177]

I recently rebuilt a 200 and noted the oiling differences...

The 175 has two vertical oil passages holes in the case. One matching the 200 and another across the case on the points side. The 200's hole is also much smaller. (see attached)

If you use 175 cam bearings, which have provisions for oiling the bearing surface on the points side, you will need to drill a matching hole into the cb200 case and head. It looks just like the passage that is used on the tach's cam holder side.

I enlarged the 200's existing oiling hole, and added one on the opposite side which smaller, to keep the pressure up. In addition i added the matching hole in the head and used a points cam holder from a 175.

You could also use an external line to the tach drive if you wanted to get fancy. There is a nice spot for an oil line.

 

[Texasstar]

I recently rebuilt a 200 and noted the oiling differences...

The 175 has two vertical oil passages holes in the case. One matching the 200 and another across the case on the points side. The 200's hole is also much smaller. (see attached)

If you use 175 cam bearings, which have provisions for oiling the bearing surface on the points side, you will need to drill a matching hole into the cb200 case and head. It looks just like the passage that is used on the tach's cam holder side.

I enlarged the 200's existing oiling hole, and added one on the opposite side which smaller, to keep the pressure up. In addition i added the matching hole in the head and used a points cam holder from a 175.

You could also use an external line to the tach drive if you wanted to get fancy. There is a nice spot for an oil line.

this is the cleanest solution I have seen if it holds up how did it hold up?

 

[bsnodgre]

Great question TexasStar...

How'd it work?

 

[acm177]

The holes in the 200 case would emulate the 175's. The external oil line would Look like the one that BertJan Used on his 200. It bypasses the oil rising through the case studs and directly to the tach side cam housing.

I haven't run the 200 engine in anything, and also didnt use the tapped external oil line, because i had found some bearing with less wear to use. I just threw the 200 together to free up some space from all of the parts laying all over the place.

They take up less space when neatly assembled into a case.

You would need to add this hole to the 200 in the case, and one in the head to pass the oil into 175's points side cam holder. In the exact location.

The pic with the external oil feed is the one from BertJan (I think) I couldn't find the thread that it was in...

 

[acm177]

I see that Bert mentioned it in one of Texasstars posts...

 

[Bert Jan]

I see that Bert mentioned it in one of Texasstars posts...

Jup. PM for info if you like. Build thread is here:
http://www.dotheton.com/forum/index.php?topic=32298.0

I also modified the other cam housing with a needle bearing. I needed to block off the tacho, the oil seeped right out. Pressure is way to high i guess for that little restrictor seal. I also modded the other cam housing (left one) by drilling the overflow hole bigger (6mm). The points got wet with oil because the seal broke aswell on that side due to high pressure. No more trouble with worn cams

 

[Texasstar]

Jup. PM for info if you like. Build thread is here:
http://www.dotheton.com/forum/index.php?topic=32298.0

I also modified the other cam housing with a needle bearing. I needed to block off the tacho, the oil seeped right out. Pressure is way to high i guess for that little restrictor seal. I also modded the other cam housing (left one) by drilling the overflow hole bigger (6mm). The points got wet with oil because the seal broke aswell on that side due to high pressure. No more trouble with worn cams

pictures?

 

[Texasstar]

The holes in the 200 case would emulate the 175's. The external oil line would Look like the one that BertJan Used on his 200. It bypasses the oil rising through the case studs and directly to the tach side cam housing.

I haven't run the 200 engine in anything, and also didnt use the tapped external oil line, because i had found some bearing with less wear to use. I just threw the 200 together to free up some space from all of the parts laying all over the place.

They take up less space when neatly assembled into a case.

You would need to add this hole to the 200 in the case, and one in the head to pass the oil into 175's points side cam holder. In the exact location.

The pic with the external oil feed is the one from BertJan (I think) I couldn't find the thread that it was in...

thanks

 

[Bert Jan]

pictures?

Lots. What needs to be on them?

 

[Bert Jan]

The holes in the 200 case would emulate the 175's. The external oil line would Look like the one that BertJan Used on his 200. It bypasses the oil rising through the case studs and directly to the tach side cam housing.

I haven't run the 200 engine in anything, and also didnt use the tapped external oil line, because i had found some bearing with less wear to use. I just threw the 200 together to free up some space from all of the parts laying all over the place.

They take up less space when neatly assembled into a case.

You would need to add this hole to the 200 in the case, and one in the head to pass the oil into 175's points side cam holder. In the exact location.

The pic with the external oil feed is the one from BertJan (I think) I couldn't find the thread that it was in...

About the picture with the 2 circles drawn - no need to drill the left hole. the oil will go the way of least resistance, so a bigger hole will lead to cam wear on the right side, being tougher for the oil to get there. Besides, on the 200 engine i worked on only the right hole was there. The left was not.

 

[Texasstar]

Lots. What needs to be on them?

the plug you made on the lathe and the needle bearing for the other side

 

[Bert Jan]

the plug you made on the lathe and the needle bearing for the other side

They're in Jene's thread. The plug is just an aluminium part with the same dimensions as the tacho cable end, but not hollow and has an extra rubber o-ring on it. I made that plug couple weeks back in a hurry because oil dripped out like no tomorrow and we wanted to ride.. so no pics of that. I could make you one but it would be pricey to ship. besides, it's not rocket science and if you plan on doing a bearing upgrade you're already halfway.
If you choose to do the external oil feed, be sure to plug the hole of the tacho and drill the hole in the left ear. oilseals will break.

 

[Texasstar]

They're in Jene's thread. The plug is just an aluminium part with the same dimensions as the tacho cable end, but not hollow and has an extra rubber o-ring on it. I made that plug couple weeks back in a hurry because oil dripped out like no tomorrow and we wanted to ride.. so no pics of that. I could make you one but it would be pricey to ship. besides, it's not rocket science and if you plan on doing a bearing upgrade you're already halfway.
If you choose to do the external oil feed, be sure to plug the hole of the tacho and drill the hole in the left ear. oilseals will break.

thanks brother

 

[Bert Jan]

thanks brother

welcome. I can make more pics if you like. Engine needs teardown to replace broken kick-axle anyway..
I'm also going to fab up custom cam ears with ball bearings, because it's nice.

 

[Texasstar]

welcome. I can make more pics if you like. Engine needs teardown to replace broken kick-axle anyway..
I'm also going to fab up custom cam ears with ball bearings, because it's nice.

we will have to come see you when we make to to the motherland some day...

 

[Bert Jan]

we will have to come see you when we make to to the motherland some day...

sure! Would be coool

 

[acm177]

About the picture with the 2 circles drawn - no need to drill the left hole. the oil will go the way of least resistance, so a bigger hole will lead to cam wear on the right side, being tougher for the oil to get there. Besides, on the 200 engine i worked on only the right hole was there. The left was not.

I had drilled the holes in the 200 case to the same size as the ones in my 175 so that I could use the 175's cam bearings on the 200. ...should have articulated that better.

Also worth mentioning-- The holes in the 200's cam surface (before the cams ramp) are larger than the ones on the 175's cam. I dont know how that may come into play when considering oiling...

 

[Bert Jan]

Ok, i did not know the 175 ears fit on the 200 head. Good to know. Whats the advantage of using the 175 ears over the 200's btw?

 

[acm177]

They have oil passages for the points side of the cam. Instead of totally depending on the oil flow through the cam. I think that is why 200s had a reputation for poor oiling.
The passage looks just like the one on the tach side.