Topic: Replacement Camshaft & Timing Chain

[wpomeroy11]

Hello all,

           I recently pulled the motor in my '74 CB750K to replace the head gasket due to oil weepage. When I removed the valvecover, I noticed that one end of the camshaft was broken off, underneath the far bushing. In testament to the venerable SOHC engine, the engine was running completely fine other than the mist of oil coming out of the head. As you all know, failure is the perfect time to upgrade, as always. I'd like to put a cam in it that helps her breathe a little better on the top end, without upgrading any valves or springs. I understand that this will probably only yield a modest performance increase. My list of things I will have to procure are as follows:

-New camshaft. Can anyone recommend a good place to find one? Everywhere I look has brands that I've never heard of, and I don't want to put crap in my engine. I'd like to spend less than 200 bucks on that.

-New valvecover and head gasket. pretty self explanatory. However much it costs for a good multi layer head gasket

-New jets for the carburetors due to the hotter cam

-New cam chain, preferably with a removable master link so I don't have to separate the crankcase. I saw a post with one of these listed for like 30 bucks, that sounds good to me.

-New tensioner? I don't know if that's replaceable without splitting the case. If not, I guess I'll end up splitting the case, as my tensioner is NG.

-New clutch plates as well. Will I also have to replace the clutch springs, or will a fresh clutch pack do the trick?

In the event that I have to get my head decked, Is there any history of anyone milling the head down to increase compression? I know you can do that on car engines, but I'm not sure if it's possible on a carbureted engine.

Sorry for the laundry list, and thanks in advance for the quick replies!

-Will

[MCRider]

Hello all,

           I recently pulled the motor in my '74 CB750K to replace the head gasket due to oil weepage. When I removed the valvecover, I noticed that one end of the camshaft was broken off, underneath the far bushing. In testament to the venerable SOHC engine, the engine was running completely fine other than the mist of oil coming out of the head. As you all know, failure is the perfect time to upgrade, as always. I'd like to put a cam in it that helps her breathe a little better on the top end, without upgrading any valves or springs. I understand that this will probably only yield a modest performance increase. My list of things I will have to procure are as follows:

-New camshaft. Can anyone recommend a good place to find one? Everywhere I look has brands that I've never heard of, and I don't want to put crap in my engine. I'd like to spend less than 200 bucks on that.

-New valvecover and head gasket. pretty self explanatory. However much it costs for a good multi layer head gasket

-New jets for the carburetors due to the hotter cam

-New cam chain, preferably with a removable master link so I don't have to separate the crankcase. I saw a post with one of these listed for like 30 bucks, that sounds good to me.

-New tensioner? I don't know if that's replaceable without splitting the case. If not, I guess I'll end up splitting the case, as my tensioner is NG.

-New clutch plates as well. Will I also have to replace the clutch springs, or will a fresh clutch pack do the trick?

In the event that I have to get my head decked, Is there any history of anyone milling the head down to increase compression? I know you can do that on car engines, but I'm not sure if it's possible on a carbureted engine.

Sorry for the laundry list, and thanks in advance for the quick replies!

-Will

Many people here have suffered a broken camshaft including me. One of the oiling holes becomes clogged and starves one side or ta other of oil, the cam seizes in the bearing and breaks. If you continue driving, as I did, you're essentially a 368cc twin with an air compressor on the side. 

[wpomeroy11]

Does that mean I currently have a oil passage blocked? Not trying for a repeat cam snapping.

Also, some other advice would be much appreciated!

[BPellerine]

with stock pistons you would have to watch how much you decked the head so the valves do not hit the pistons,cx1 camshaft from cycle x is supposed to be drop in,you will have to remove the barrels to replace the tensioner,have no personal exp with a master link camchain,prefer endless.billp

[754]

Used cam 20-50 bux most of the time.. Sold a NOS 72 cam for 110.00 about 15 months back..

[wpomeroy11]

I think I'm trying to get a slightly hotter camshaft. Any leads?

[wpomeroy11]

The Cycle X stuff looks pretty nice. Is that a pretty standard price for a cam? It seems odd, I can get a racing cam for a mustang for less than 200 bucks but this stuff is well over it.

[754]

Our cams are very cheap.. At 250 ish
Cant get one for my Honda twin or single any cheaper.. Harley twin cyl cams, same thing.. Cannot compare our stuff to mass produced car stuff..
 Used hipo 750 cam. Usually 125-175..

[wpomeroy11]

Thanks for the information, I thought about the economies of scale but didn't think that it would be that significant. Where can I source a used hipo cam?

[BPellerine]

you could post in wanted section for a later 77,78 f cam,or hipo cam for stock engine,if you are looking for a little bit of power,cant put anything big with stock engine.billp

[PeWe]

Cam broken due to no oil? Open the entire engine is minimum for me. You need to clean it and verify all parts.
The primary chains with tensioner is most likely garbage if you have not done a complete repair. Good idea to verify crank with bearings too.
It is no problem to open the engine completely. The worst thing is to take it  out  from frame and in again.

You can still find cheap internal parts on eBay sold by US sellers. If you live in USA the shipping is almost free. For me higher shipping costs than the parts. It's not that much anyway. I have bought 3 sets of cam holders the last year just for sure when they all were from low mile bikes and cost just a little. The last set costed $25US. Other sets complete with rocker arms and everything, cam included.
I'm currently waiting for a complete K6 clutch with primary hub that costed 50 bucks, shipping >$70... VAT and customs will add +30%. Despite that around 160 Euro in total.

Clutch: Use std clutch with barnett springs or similar. Racing clutch can be a problem when plates stick together over night. I had to replace my Cyckle X plates, replaced with plates from cruzinimage. Works really well in my engine with +80 rwhp.

Old clucth: http://www.ebay.com/itm/HONDA-CB750K1-CB750K2-CB750K3-CB750K4-CB750K5-SEVEN-CLUTCH-PLATE-SET-CD-1133-/141432925416?vxp=mtr&hash=item20ee0f2ce8

Newer as to my K6 (the outer plate has wider ears)
http://www.ebay.com/itm/76-78-HONDA-CB750K6-CB750K7-CB750F2-CLUTCH-FRICTION-PLATE-1145-/161408453864?vxp=mtr&hash=item2594b18ce8

[MCRider]

Does that mean I currently have a oil passage blocked? Not trying for a repeat cam snapping.

Also, some other advice would be much appreciated!

Yes, the offending passages are between the head and the cam bearing stand. The oil is forced up the 2 studs in the rear, either side of the chain tunnel. It usually only happens after a rebuild when a piece of dislodged debris finds its way into a passage, travels up the stud cavity. Near the top, there is a passage allowing the oil to divert to the orifice in question where it gets stuck and dams up the oil flow.

You will uncover the orifice when you pull the trashed cam bearing stand.

[edwardmorris]

Used cam 20-50 bux most of the time.. Sold a NOS 72 cam for 110.00 about 15 months back..

Actually $150, but that is still wayyyyyyyyyyyyyyyyy cheaper than the $900+ on ebay for NOS ones. Thanks again for it, its one of the best things running on my JMR head

[wpomeroy11]

You guys are some of the most helpful people on the planet. Props around to all of you.

I have so much information to digest, and I'm going to definitely post a wanted ad in the forum for some go faster parts.

When I opened the valvecover, there was some sharpie on the cam towers indicating which cylinder is which. I reckon some guy rebuilt it fairly recently... maybe 5 years ago.

Here's a little treat for you guys to see what I'm working with!

The bearing cap has what I will choose to call "Seriously good hone." Should be able to slap it back together right? Right? 

The cam tower is equally as sad. That's gonna need replaced too.

If you look at the cam, all is well... until the last cam bearing.

Finally, there's a lot of burnt and hardened oil in the valley on the valvecover where the cam snapped. On the healthy end, the oil was as happy as Larry.

In other news, the cam chain looks excellent. I will be replacing the tensioner, but I reckon the chain itself should be good to go, pending further investigation.

My list is expanding to a new cam tower, as well as the clutch springs and fresh clutch discs.

[wpomeroy11]

http://imgur.com/a/Y0CTu

Pictures really did not want to post on the native uploader, had to use imgur.

[scottly]

Here's a little treat for you guys to see what I'm working with!
If you look at the cam, all is well... until the last cam bearing.

Uhh, I can't see anything?

[wpomeroy11]

http://imgur.com/a/Y0CTu

Pictures really did not want to post on the native uploader, had to use imgur.

@Scottly, check this! It's an imgur album. Pictures refused to upload natively on the forum.

[scottly]

Ok, I see them now. That is very unusual to have only the very end of the cam break off!!

[754]

900 bux.. For a cam.  Wow , i should list my unobtainium NOS oil pump starting at 600..

 Was you engine still running? 
 Mine looked like this and still ran, the last hour going over a mountain pass at 60-70 mph.. But it seemed sluggish..

 I do have a cam somewhere that looks like yours just before yours broke

 I think mine was seizing a bit after stopping, or it felt tight, but electric starter broke it free and started.

[edwardmorris]

900 bux.. For a cam.  Wow , i should list my unobtainium NOS oil pump starting at 600..

Yep, NOS only and I saw two different listings in the past couple years. Don't sell off that oil pump! It HAS to be the last new one

[wpomeroy11]

Shockingly, it ran like a top! all 4 cylinders were running great with no issue, even all the way up to redline. The only reason I even took the engine out was to replace the head gasket. Seeing a snapped cam was a shock.

[MCRider]

Shockingly, it ran like a top! all 4 cylinders were running great with no issue, even all the way up to redline. The only reason I even took the engine out was to replace the head gasket. Seeing a snapped cam was a shock.

Yes, yours was not the full cam snap like others have had. IT usually seizes in both bearings of one side or the other, and breaks on that side of the cam sprocket, silencing 2 cylinders. Still, same problem. Oil passage plugged up.

Was it ever opened up before? Rebuilt?

[wpomeroy11]

Yeah, it's definitely been rebuilt before, but not by me. This is my first experience in rebuilding a motorcycle engine. My entire experience of engine work has been on cars, but it's pretty transferable.

[MCRider]

Yeah, it's definitely been rebuilt before, but not by me. This is my first experience in rebuilding a motorcycle engine. My entire experience of engine work has been on cars, but it's pretty transferable.

That explains it. I've never seen a cam twist that wasn't a result of a rebuild where some loose debris is not cleaned out and it clogs the orifice.  Often, its the use of a silicone gasket sealer that gets hard. Sealer squeezes to the inside as well as the outside of the engine. You can clean the outside off, but the inside goop gets hard and breaks off and clogs the orifice.

Lesson: always use non-hardening gasket sealer.

[wpomeroy11]

Lesson learned.

Unfortunately, I have to track down the clogged passage now.

When I find it, will it be apparent, or is it one of those things that you have to clear every passage and pray you got it? Hoping for the former.