Topic: Refurb or replace - Valve Guides

[exponent]

In doing work on valves and head, I am yet to check valve guide clearance and runout.

I know I really should but we don't have a press and not inclined to drop a lotta cash on shop work

Will my compression be too far off if I don't replace guides? Valves are new. Chance of grenading the head?

Thanks dudes

[bryanj]

You wont know till you check clearance, if its in spec its ok if out replace

[Dunk]

Measure clearance. After cleaning put a dial indicator on the valve as close to the guide as possible, lift valve off seat and firmly move it side to side. Valve guides are cheap enough, as is a install/removal tool for your air chisel, and a guide reamer. Cost is in the seat cutters. If you'll only ever do one head in your life just pay a machine shop to save a few bucks, tools pay for themself after the second time you use them. Either way, measure valve to guide clearance first, may be within serviceable limit and you can just lap valves and replace seals.

[HondaMan]

Which engine is this, and about how many miles does it have on it?
The CB500/550/350F/400F/650F heads seldom need more than cleanup of the valve faces and lapping between them and the seats to clean things up.

The 750 is another story.

[PeWe]

CB750 has often bad ex guides on those heads I have bought used.
My K6 neded some replaced after 65000 km.
But this depends on correct lash used (not too small),  running hot or not that also can ruin the valves.

Easy to check.
Remove springs, let the valve be open 10-15 mm and try to wiggle it sideways holding the valve head .
If there is a clear play, replace guide, cut seat,  new valve + seal.
I have told my experienced shop to replace when it is OK for now, but too much when head already is off.

This is like other things that can be actual in the engine, not bad enough for taking it apart, but not good enough to assemble it.
Redo things cost time, gaskets and additonal work to take it apart again.

Give throttle to higher rev, release throttle, check mirrors when open throttle again. When your biker friends will complain or you cannot se the cars behind you, time for a repair.

It is not fun to ride a smoker either.  Chambers and ports  in head need to be cleaned plus the piston crowns.

I'm sure the opposite is OK, a smooker can enjoy the ride.

I read in another recent post that Honda stock valves are very soft under the coating. Lapping not recommended, valve will quickly degrade.

[Bodi]

The valves can be lapped without worry, but regrinding can go through the Stellite hard surface ... that exposes the softer steel underneath which will not last nearly as long as the hard Stellite surface would.
Stellite valves have a layer of cobalt tungsten alloy deposited over the steel valve blank. Factory grinding to the final dimensions removes some of it.
I haven't found a spec for the actual Stellite thickness remaining on OEM valves but what I can find about it suggests that the minimum applied thickness is around 1mm, if you're lucky a very light grind may be ok.
Stellite was common in stuff like machine tool cutters before carbide insert tooling was developed. Still used in a lot of things.

[Little_Phil]

The CB500/550/350F/400F/650F heads seldom need more than cleanup of the valve faces and lapping between them and the seats to clean things up.

I've looked at six 500/550 heads in the last few years. A couple I know had nearly 50 000 on them. All were fine except the 78 550K that I have the exhaust valves were completely shot. It was completely standard, only showed 21 000 and that looked straight and the engine didn't look like it had ever been apart.

[bryanj]

Personaly i put that down to the pd lean burn carbs required for emission regs, i point blank refuse to work on the damn things!

[HondaMan]

The CB500/550/350F/400F/650F heads seldom need more than cleanup of the valve faces and lapping between them and the seats to clean things up.

I've looked at six 500/550 heads in the last few years. A couple I know had nearly 50 000 on them. All were fine except the 78 550K that I have the exhaust valves were completely shot. It was completely standard, only showed 21 000 and that looked straight and the engine didn't look like it had ever been apart.

I suspect that the '77-'78 heads also got less expensive (cheaper) exhaust valve guides, if not on both sides - and certain electrical parts. This was the era when Sochiro had lost control over his company and it fell into the banker's hands as the great expenditures began for the expansion into building Honda cars. The CX500 bikes got a cheaper-materials alternator (which caused most of them to fail), the 750F2/3 and K7/8 bikes got cheaper valve guides, swingarms, brakes and electric switches, and the GL1000 got poor rear shocks and too-thin front fork tubes, all from this same era. Things got better in the Honda bikes by 1984 after the embarrassment led to Kawi whipping Honda in sales and marketing with the bikes, but their good stylists had left for greener pastures, so the bikes never recaptured the market as they once had.

[exponent]

Measure clearance. After cleaning put a dial indicator on the valve as close to the guide as possible, lift valve off seat and firmly move it side to side. Valve guides are cheap enough, as is a install/removal tool for your air chisel, and a guide reamer. Cost is in the seat cutters. If you'll only ever do one head in your life just pay a machine shop to save a few bucks, tools pay for themself after the second time you use them. Either way, measure valve to guide clearance first, may be within serviceable limit and you can just lap valves and replace seals.

Been trying to find a decent dial gauge for runout, might go on amazon and get one this week. I'll kick myself if everything goes back together and the guides are causing problems. Riding season is still a month and a half away where I am so I have time.

Which engine is this, and about how many miles does it have on it?
The CB500/550/350F/400F/650F heads seldom need more than cleanup of the valve faces and lapping between them and the seats to clean things up.

The 750 is another story.

78 550 with 24k

Looks like I'll be replacing guides, anyone have a link to buy the guide press tool? Keen on having reliability, and stocking tools is what we do in our garage, dad and I are running out of room lol. Valve spring compressor is coming today but I'll wait to use it so I can measure everything.
The hasty fool learns from you

[bryanj]

550 with 24k shouldnt need guides.
You dont need a dial gauge just carefully remove burr at top of stem and roll the stem on a steel table, if the head dont wobble its ok

[Little_Phil]

As said my 78 550K (11/77 manuf) the exhaust valve guides were gone at apparently 21k. Didn't need a dial gauge they were that bad. Just bought another complete head with agreement that I would return it if the guides were gone. Agree with Hondaman about company standards at that time. The paintwork on the frame was waffer thin.

[MRieck]

Measure clearance. After cleaning put a dial indicator on the valve as close to the guide as possible, lift valve off seat and firmly move it side to side. Valve guides are cheap enough, as is a install/removal tool for your air chisel, and a guide reamer. Cost is in the seat cutters. If you'll only ever do one head in your life just pay a machine shop to save a few bucks, tools pay for themself after the second time you use them. Either way, measure valve to guide clearance first, may be within serviceable limit and you can just lap valves and replace seals.

Been trying to find a decent dial gauge for runout, might go on amazon and get one this week. I'll kick myself if everything goes back together and the guides are causing problems. Riding season is still a month and a half away where I am so I have time.

Which engine is this, and about how many miles does it have on it?
The CB500/550/350F/400F/650F heads seldom need more than cleanup of the valve faces and lapping between them and the seats to clean things up.

The 750 is another story.

78 550 with 24k

Looks like I'll be replacing guides, anyone have a link to buy the guide press tool? Keen on having reliability, and stocking tools is what we do in our garage, dad and I are running out of room lol. Valve spring compressor is coming today but I'll wait to use it so I can measure everything.
The hasty fool learns from you

You have to bead blast or vapor blast the ports to remove carbon etc from the guides. Heat the head to about 250F and the drive the guides out with a 5.5mm drift and a heavy ball peen hammer. Drifts aren't that expensive.....do a search. Walmart was selling a 5mm and a 5.5mm for 16.98. Make sure the bore is clean before installing new guide. Heat the head again and drive in from the top of the head. Go easy at first as the guide has to align itself in the bore. You will need to replace the valve guide orings prior to installation.
 You can measure the guide bore with a ball gauge but I've haven't had a problem with the OEM iron guides in regard to interference fit.
 The guides will need to be reamed or honed for the valve to fit.....you can bank on that. I prefer honing as it is more precise and leaves a better finish in the bore.

[PeWe]

Easier to take the head to a shop that knows these bikes.

Seats to be properly cut after guide replacement.

[MRieck]

Easier to take the head to a shop that knows these bikes.

Seats to be properly cut after guide replacement.

Seeing how the guides need to be sized after installation and a valve job done why not just have them do everything.

[PeWe]

Easier to take the head to a shop that knows these bikes.

Seats to be properly cut after guide replacement.

Seeing how the guides need to be sized after installation and a valve job done why not just have them do everything.

I have heard about one good shop in Ashland Massachusetts where  guys sends their heads and other stuff for restore and going faster!

[bryanj]

Just send it to Mike and get it done right first time, and inside the forum

[bwaller]

I don't know about that guy.   

[bryanj]

The very same MRieck that has been answering your questions!!!