Topic: CB450 top end woes.. what gives?

[quietlikeachurch]

Recently picked up a 72 450 for a song, ~22K miles, thought it was in OK shape..

..Until I cracked the engine open to replace some gaskets.  From the cylinders down all seems great, but the head is wrecked.

Both cams are heavily scored bearing-side and worn on the lobes.  cam bearing cups and followers are in poor condition and the tips of the valve stems have scoops in them.

I assumed this engine had been beaten up and asked around town for spares and almost everyone had piles of 450 parts with the same symptoms.

Whispers of poor oiling make sense but the root cause must be a combo of many factors.  Does anyone here have a concrete explanation as to why these bikes tend to eat cams?  And if so how the heck does one make a 450 reliable?

[fendersrule]

The CB450 can be just as reliable as the CB750.

The thing is, the CB450 is easy to screw up and cause major damage.  Sort of like the CB125: if you miss an oil change, you can kiss that engine goodbye. Otherwise, it's damn-near bulletproof.

How to mess up a CB450 #1:
The CB450 needs its valves adjusted consistently. It's more trickier and less "approachable" than the CB750. The CB750 can be adjusted in an hour, tops without any disassembly. The CB450 requires pulling off two valve covers (likely wrecking at least one gasket) and removing the carbs and air box. The valves are adjusted using a turn rod that is located on both sides of the engine. There is a certain direction and tolerance that the flat head screw has to be. Not only do you have to make sure the valves are set to a very very small tolerance, but you have to pay attention to where the flat head screw ends up. If one didn't have knowledge of this, they could turn the screw past tolerance, and I could easily see major damage occurring. This is possible in your case.

How to mess up a CB450 #2:
The CB450 requires consistent periodic oil changes, like the CB125 (and probably CB350) because it doesn't have a replaceable oil filter. It's nice that you never have to replace it like you do the CB750 (and worry about having a spare seal on hand) but you have to put it back together properly since it's centrifugal. If you don't put it back together correctly, the top end won't get oil.

[faux fiddy]

Sounds like good info, I'm just getting to my valves, some [factory] say .0012,  but I found a Hondatwins.net  thread.  Team Hansen people said to go a tight   .002 so that's what I went with. Those guys won Daytona with an early  with the same basic motor.

[Retro Rocket]

The CB450 can be just as reliable as the CB750.

With a lot  more maintenance, they really are not comparable in that sense

The thing is, the CB450 is easy to screw up and cause major damage

The 750 isn't they are almost bullet proof, I've seen examples that haven't had an oil change in what looked like years but cleaned up and ran well, can't do that with a 450 i'm afraid..... Oh and your rod is called a torsion bar....   Impressive eh....

[rb550four]

http://www.hondatwins.net/   , These guys eat this stuff for breakfast, nice  group, even some members from here. Got answers for my 450 there. good luck.

[jas67]

The CB450 requires consistent periodic oil changes, like the CB125 (and probably CB350) because it doesn't have a replaceable oil filter. It's nice that you never have to replace it like you do the CB750 (and worry about having a spare seal on hand) but you have to put it back together properly since it's centrifugal. If you don't put it back together correctly, the top end won't get oil.

Most, if not all of the 60's and 70's Honda twins (and singles) have no replaceable oil filters.   The twins pretty much all have this spinner instead.   So, bottom line is, change the oil VERY often, like every 1,200 miles, more if you ride it hard, and/or in dirty/dusty conditions.