Topic: Which valve guides (CB750 K0)

[kaysystems]

I've been pumping oil out of the exhaust manifolds since the spring.

Took the engine apart this week and It's time to replace the valve guides.

My question is: Should I use original Honda ones without seals (they have a tapered top) or ones with a seal. I'm wondering if the seals degrade due to exhaust heat.

thanks

David

[MRieck]

 I don't believe those early exhaust guides are available anymore. Use seals.

[HondaMan]

Those early ones (pointed) could not use seals. The ones from late K3 thru K6 will fit, I believe, in the K0. I know they fit into my K2, but don't work as well at (real) hi RPM in RR conditions, because they lacked the extra length of the earlier ones. The valves run more accurately with the longer guides and no seals.

Terry....?

I'm interested, though: I have seen VERY few K0-K3 bikes blow oil from guides. The guides were very hard and the valves stellite: mine only wore .0007" in 112,000 miles, and were not letting oil out. This issue sounds like high crankcase pressures(?). That will push oil up the rings during the end of the exhaust stroke, then out into the pipes. Late timing, particularly on the 2-3 cylinders, will do this to an otherwise OK engine, too. The K0-K2 were notorious for having erratic timing on the 2-3 side of the points advancer, and also for the advancer sticking at either idle or some mid-point position from rust (the K3-later ones were plated to reduce rusting).

Throw a timing light on it, and see if there isn't "jitter" on the 2-3 points, or maybe a stuck advancer. If so, check the FAQ for how to fix this to see if it might stop that oil leak(?).

[kaysystems]

When I got the bike I was blowing oil out of the rear sprocket seal. Somebody connected the breathers all wrong. That is sorted out.

I checked one of the valves and the side to side play is just over max as stated in the Honda manual. The valves faces were 'tidied up' by a repair shop last January, an dsince then I'm really leaking. He said the valves were OK. I need to measure them, but I can see a lot of play in the one exhaust valve I have checked.

So while the engine is apart I want to replace the guides. I can get original guides from David Silver, CMS, or even our favourite eBay.

Just wondered what to buy. In theory sealed ones are better, provided the seals will last.

David

[MRieck]

 I prefer Kibblewhite Ampco guides. They are honed to fit and the material sheds heat much better than OEM. They take seals. Don't worry about the seals "lasting" as long as you use OEM pieces. You will need a valve job after installing new guides....none of this lapping stuff.

[kaysystems]

Thanks Mike
Forgot to mention one thing.
A few weeks ago, on my way to work one very cold morning (probably around 35F) The oil light came on after less than half a mile. What the??? There was no oil in the tank. Waited 5 mins & restarted....oil pressure after a few seconds. Continued slowly. Checked the oil when I got to work (10 miles) and there was plenty. I'm using the same oil as always and have ridden at 28F before. So where did the oil go?
My one other difference from last year is the installation of HD studs, which i figure reduce the oil return from the head so the oil stayed up there. This can be seen by starting the engine. The oil level drops and only comes back up after the engine starts to feel warm.
So with all that oil up there & loose exhaust valves I'm not surprised to see very wet manifolds.

David

[HondaMan]

The K1 and K0 both used to do this "hiding the oil" bit, often in cold weather, and usually with 10w40 oil. "The check valve in the oil pump sticks open and slowly drains the tank into the crankcase". Honda never officially issued a bulletin about it, though.

In 1970, for a brief time, we were warranty-changing oil pumps on those models of 750, quite a few. The problem seemed to go away later, never saw it after 1970. I personally changed 3, the shop changed many more. At Spring Honda, only the Service Manager would do it, then talk quietly on the phone to someone at Honda. He never would tell me what the deal was...at Brown's, I changed all the (complaining) ones that came into the Pekin branch, as I was that Service Manager. There was a special form to fill out, and the bike had to have a "before this number" engine number to get it under warranty. I did 2 K0 bikes and one K1 that I remember.

If my old K2 sits for 3 months (winter), it drains almost 1/2 of the 3+ quarts down into the cases. that's why I'm a-fixin' to change out my pump. It's in the check valve, or in the little O-ring that mates to the bottom of the crankcase. Personally, I suspect the O-ring, because they shrink in cold, while a check valve typically gets stiffer....

[Big Jay]

I prefer these;
http://cbrzone.com/valves.html

[HondaMan]

Thanks Mike
Forgot to mention one thing.
A few weeks ago, on my way to work one very cold morning (probably around 35F) The oil light came on after less than half a mile. What the??? There was no oil in the tank. Waited 5 mins & restarted....oil pressure after a few seconds. Continued slowly. Checked the oil when I got to work (10 miles) and there was plenty. I'm using the same oil as always and have ridden at 28F before. So where did the oil go?
My one other difference from last year is the installation of HD studs, which i figure reduce the oil return from the head so the oil stayed up there. This can be seen by starting the engine. The oil level drops and only comes back up after the engine starts to feel warm.
So with all that oil up there & loose exhaust valves I'm not surprised to see very wet manifolds.

David

Most of the oil return from the head is down the center, where the camchain runs. The studs's tunnels are the oil feed up to the top of the engine.

The dropping oil level in the tank during cold startup is due to the leakage that filled the crankcase with some of the oil when it was stopped. After the scavenging starts from the transmission, filling the rest of the oil pump, part of the scavenged oil makes its way back to the tank, while part of it is sent through the transmission's shafts to lube the gears.

[Bob Wessner]

What is the long-term harm of this leak down? Mine has done it forever.

[kaysystems]

Most of the oil return from the head is down the center, where the camchain runs. The studs's tunnels are the oil feed up to the top of the engine.

The dropping oil level in the tank during cold startup is due to the leakage that filled the crankcase with some of the oil when it was stopped. After the scavenging starts from the transmission, filling the rest of the oil pump, part of the scavenged oil makes its way back to the tank, while part of it is sent through the transmission's shafts to lube the gears.

I can start with a cold, full tank and watch the level drop and slowly come back after a couple of minutes.
Maybe I'll change some pump seals while the enging is out.

But even if most of the drain is throught the cam tunnel, are the valve guides going to get a bit swamped with oil until everything warms up? The pumping action of the spring plate won't help.

David

[HondaMan]

I can start with a cold, full tank and watch the level drop and slowly come back after a couple of minutes.
Maybe I'll change some pump seals while the enging is out.

But even if most of the drain is throught the cam tunnel, are the valve guides going to get a bit swamped with oil until everything warms up? The pumping action of the spring plate won't help.

David

No, the guides are up out of the oil, at least at their seal faces (or ends, if yours has the tall, seal-less type). The rather efficient top end oil spreading system does a pretty good job of lubing the valve shafts with splatter oil from the adjacent rocker arm. Oddly enough, polishing the rocker arms for less weight makes the oil fall off and not lube these valve stems and springs, in turn letting them wear more. But, when oil does get onto the valve shaft, the seal is supposed to disperse it. On the K0-K2 guides with their pointed top end, the guide just barely reaches above the splatter point, so only a tiny bit of oil can make it into the guide. When the guides were shortened to allow use of a seal (late K2 on), cracked seals that leaked oil into the guides soon became an issue. The guide clearances could be .003" or more on the old engines and very, very little oil was used, but a slight crack in a seal on an otherwise in-tolerance shorter guide makes for lots of smoke and mess.

Honda's goal with the seals was more about reducing pollution (crankcase blowby reduction) and reducing the amount of expensive valve guide material they used at that time. The stellite alloys they used back then were quite expensive, even today.

[HondaMan]

What is the long-term harm of this leak down? Mine has done it forever.

Mine has done it since the 1970s. I usually crank the kickstarter over about 40-50 times if I see low tank levels after a long time sitting. This seems to fill up the passageways so that when I start it up, the pressure comes right up, too.

...yes, my kickstart lever is slightly bent from all those times....I've straightened it up more than once....

When the bike has been run for a ride, then shut off, the oil that remains in the bearings is hot and thin, and much of it drains out easily while things cool off. The same can be said for the little tiny leaks around the oil pump, I'm sure. That was the trouble point with the K0-K1 engines 'way back when. I will have to go find one of my oil pumps and make a pix of how to "fix" this, given what we have to work with today.

To prevent bearing damage over the Winter sojurn, I have always gone back out the next day after the long ride and started the bike up for about 2-3 minutes. then shut it off. This reprimes everything and puts thicker oil back into the bearings, not so likely to drain off. It also fills up the journals everywhere. The subsequent startup, months later, is always much easier and mechanically quieter. I do this with my cars, too, and have received well over 250,000 mile engine service on dino oils from "old tech" engines that were purported to only reach 100,000 or so. If I ran my bike real hard, or in real hot, slow traffic on my 1.5 hour-long commute to home last summer, I would go back out around 8-9 PM and run the bike for a minute or two for the same reason. The next morning, it starts far easier than if I forget to do this.

[kaysystems]

[/quote]

No, the guides are up out of the oil, at least at their seal faces (or ends, if yours has the tall, seal-less type). The rather efficient top end oil spreading system does a pretty good job of lubing the valve shafts with splatter oil from the adjacent rocker arm. Oddly enough, polishing the rocker arms for less weight makes the oil fall off and not lube these valve stems and springs, in turn letting them wear more. But, when oil does get onto the valve shaft, the seal is supposed to disperse it. On the K0-K2 guides with their pointed top end, the guide just barely reaches above the splatter point, so only a tiny bit of oil can make it into the guide. When the guides were shortened to allow use of a seal (late K2 on), cracked seals that leaked oil into the guides soon became an issue. The guide clearances could be .003" or more on the old engines and very, very little oil was used, but a slight crack in a seal on an otherwise in-tolerance shorter guide makes for lots of smoke and mess.

Honda's goal with the seals was more about reducing pollution (crankcase blowby reduction) and reducing the amount of expensive valve guide material they used at that time. The stellite alloys they used back then were quite expensive, even today.
[/quote]
I have at least about 4 thou, (quick measurement with a dial guage on the valve at the top of the guide).
Here are some pictures. The bores seem dry, and clean. The area where the head gasket metal seal ring go are very clean. I can still see where I used the scotchbrite pad, on the cylinder & the head. But look at the oil slick coming out of the head. There is carbon in the cylinders because I was running only 10 miles to work. It wasn't warming up totally, and there are quite a lot of stop-starts. I had a re-bore less than 7000 miles ago. There are still honing marks on the cylinder walls.
I still assume that I'm leaking through the guides.

[MRieck]

 Put in new guides.....you need them. You will need a valve job after that too. It will be interesting to see what the 45 degree face of the valves look too.

[HondaMan]

Yeah, 4 thou is a lot of guide wear!     I am a little curious about what could have caused this wear, as it's pretty unusual, in my experience. One thing that comes to mind: I have seen tilted base spring cups (something got under one edge), which can cause side loading and also help wick the oil up to the guide lip. But, a thorough cleaning was all that was required for that one.

[kaysystems]

I'm not sure what happened. It was fine last year & the head went in to have the seats re-cut & lapped. Maybe he passed a reamer or something, I just don't know. The top of the guides looks a bit flattened compared to a new one, so perhaps he tried to put the guides in further & then reamed. Dunno. I now need to find someone to do it properly, without charging an arm & a leg.

David

[kaysystems]

Put in new guides.....you need them. You will need a valve job after that too. It will be interesting to see what the 45 degree face of the valves look too.

Kinda difficult to photograph with my cheap & cheerful, but here we are.

[HondaMan]

Yep, they sure are oil soaked!   

[754]

You know it sort of sounds like the guides may have been OVERreamed??

If you got .004 on one, I would check them all..

[kaysystems]

You know it sort of sounds like the guides may have been OVERreamed??

If you got .004 on one, I would check them all..

Yep. That was the worst leaker, but they are all bad.
New guides all round. I haven't checked the inlet yet.

David

[kaysystems]

Took all the valves out this morning. All the exhaust guides look like they have an oil film in the bore, and they seem to be above 3 thou. The inlets are not much better and the 'new' seals that were put on were pretty dry.
The valves have 5 thousand miles since new, so I'd like to use them if I can.
Need someone to do a good job. Where are you Mike. I'm in Montreal.

David