Time for a head job? Or just keep grinding?

[gorbys]

So I've got the head cleaned, and now I've started to lap the valves. Intake valves came out good. But the exhaust has some pitting still after a couple of rounds with coarse paste. I measured the ribbon on the valve to be about 0.97-1 mm and the service manual says 0.9-1.1mm 

So do I keep grinding or do you think its to far gone? 

 

Edited March 23, 2021 by gorbys

[wraith]

I think you've answered your own question.

If manual is saying max 1.1mm and you're already at 1mm with some still left to go.

If it was me I'd finish lapping the valves in but know it's most probably be a full head job, and as your there put some new valve guide in and maybe a porting job as well 

[gorbys]

I'm at 1.1 now and haven't got all of the pitting away. This is looking bleak... 

If I have to drill the seats do I require new oversize valves? Or if the seats can be replaced do I reuse the valves I have or buy new ones? Mind you one valve is now at the upper tolerance limit. 

Yeah I would love to do a porting and bigger valves and cams and all that but it's just not in the budget. A simple overhaul with fresh gaskets and seals was basically all I could afford at the time being 

[gorbys]

1 minute ago, TonyGee said:

what you've done so far is gona be an improvement,  a nice fresh cut seat would be nice but if the budget won't allow it then it'll have to do. how did the bike run before you pulled the head off ?  ive seen worse exhaust seats before and the motor ran fine.  i know what its like working too a tight budget   

I have no idea, I bought the engine second hand from a motorcycle breaker. He said the engine needed new stem seals because it was using oil. So I thought easy peasy, until I took the head off and found the pistons, valves and chamber covered in thick carbon deposits. So it's obviously been burning oil for a long time. 

[gorbys]

19 minutes ago, TonyGee said:

are you putting new rings in ? 

Wasn't the plan no. I haven't checked their specs yet though. 

[Joseph]

Lapping valves is a waste of time. Proper seal is obtained by having the seats done properly. You might as well have it looked at, we're not in 1940 anymore.

If you close up the engine on a budget, but have to buy at least a new set of seals soon down the line it will hardlt have been worth all the initial effort will it ?

[Gixer1460]

12 hours ago, Joseph said:

Lapping valves is a waste of time. Proper seal is obtained by having the seats done properly. You might as well have it looked at, we're not in 1940 anymore.

If you close up the engine on a budget, but have to buy at least a new set of seals soon down the line it will hardlt have been worth all the initial effort will it ?

Unfortunately I concur - its a case of where do you stop! Personally that pitting doesn't look terrible - i'd use it at a push! With the amount of carbon its a strong possibility the rings are shot so you'll have to check them and make a judgement call whether to re-use them and risk a smokey engine with a limited lifespan whilst saving for a proper job or spend the money now! 

The valve seats just need a 'kiss' with a cutter and valve's could be re-cut in a lathe or grinder. That will recess the valves a little but not enough to make a huge difference unless valve lash is shim adjusted as they'll all be wrong. Rings - if bores are within spec, I'd glaze bust them / VERY light hone and use new rings. You are spending out for a top end gasket set whatever you do so no further expense there. No idea on cost but shouldn't be that spendy except for the rings!

[Joseph]

An Uncle of a friend of mine was a engine mechanics teacher at a pro high school.

His technique for valve lapping :

Take the head apart, put valve grind paste on the seat of a valve

Put valve back in the head.

On the cam side of valve in head, fit the valve like a drill bit into an electic screwdriver

Lap the valve like so, rotating and from time to time pushing the valve in slightly to even the paste out.

Quick and very efficient, but still a bodge job in his own words, nothing is more efficient than proper machining of the seats.

 

[gorbys]

Yeah if you search YouTube for "how to lap valves" there's a ton of videos where people use drills to spin the valve while lapping. Also several people explaining why you shouldn't 

 

As for the oil burning i definately can't rule out worn piston rings either, but I do feel that since each and every one of the valve stem seals shattered like glass upon removal that that's the main issue... I have yet to measure and inspect the pistons/rings and bore yet as I've been too occupied with other stuff these days. I'm crossing my fingers they're good but with the luck I'm having lately.... 

 

I also received a reply from the local engine shop and they said they could grind the valve seats. Replacing them would be really expensive though. They also said a little bit of pitting wouldn't necessarily be the end of the world as long as its not leaking. So like you said if I'm in a pinch... 

 

 

[cnap504]

Address the oil burning issue; guide seals and cylinder sealing.  A tight budget may not allow for new seats, the bit of pitting I see isn’t terrible.  It’s a used motor you don’t know alot about so get it running inexpensively and go from there 

[dago]

Refit the valves and springs, fit spark plugs, turn head upside down and fill combustion chamber with petrol, look in the ports to see if leaking, of no leaks you're good to go

[gorbys]

I was told to use windshield washer fluid by the guys who run the machine shop. 

[dago]

 I would have thought that was the advantage of checking with petrol, if it holds it's obviously good, you can't leave it to long due to evaporation. Not saying it's the only or right way to check

[dago]

That's the way they check them where I take car heads, it's not done for long so you get quick result valve grinding is one of those topics like which oil to use, or how to run engine in everyone got there own ideas 

[dago]

Just my thoughts, the valve seat cutter does not cut the seats exactly the same as the valves are made, similar to rebore and new pistons, grinding valves in is the same as running in, mating one suffice to another. Just my thoughts on the matter, they are 40 year old engines and tolerances are different. I've had them seal with similar pitting with quick petrol test 

[dago]

Tell me about it, them poor 5 valve head yam guy's. You've got to remember they only shut for a fraction of a second and have about 150 psi pushing them into their seats

[Swiss Toni]

13 hours ago, TonyGee said:

one thing i do know is, grinding 16 valves in is the worst job to do on an engine    

Unless you have a certain 6 cylinder, from ‘somewhere else’!

[Isleoman]

On 3/26/2021 at 5:51 PM, dago said:

Tell me about it, them poor 5 valve head yam guy's. You've got to remember they only shut for a fraction of a second and have about 150 psi pushing them into their seats

Yea but,  the five valve Yamaha heads are pretty ultra reliable.  I've had two 1000cc heads go 150K miles without ever even adjusting the valves.  My current one still lifts the front wheel with ease, no smoke, 50 mpg, and only within spec oil use.    My 4 valve Suzuki was rebuilt three times in 100K.  When I get it back together it will be a 4th time.    

 

 

[gorbys]

So for the water test the valves need to be assembled with springs and everything? 

[dago]

Yep springs, retainers and collets on and turn upside down

[gorbys]

7 hours ago, dago said:

Yep springs, retainers and collets on and turn upside down

Cool. How long do I leave it sitting? 

[dago]

I normally use petrol if it doesn't leak after about 30 seconds you're fine , water  I'd probably leave for a few minutes

[gorbys]

16 minutes ago, dago said:

I normally use petrol if it doesn't leak after about 30 seconds you're fine , water  I'd probably leave for a few minutes

Oh, I fucked up a little bit then as I've left it for the last hour 

There was some moisture in the exhaust ports. But yeah, it's sat for the last hour so. Probably not that bad 

[gorbys]

I tested again today with good success but then idiot me managed to snap a piston ring when removing them so time to learn how to hone cylinders as well I guess and buy some new piston rings... And off course everything is closed now because some long haired hippie died two thousand years ago....