Valve lapping ?

[Yard Dogg]

Last time I checked on having a set of heads done, it was $150-$250, worst case scenario. That would include new guides, and it was for a V8. Just to cut the valves, is not expensive. Or, the tools to cut them yourself is another option. Lapping is not going to achieve a lasting effect. It only exaggerates an undesirable effect, which is a worn out valve. If your going to remove material from your valves, do it against a device that will remove the material the right way.

[LoHo]

Well, now we have what we often get here, different guys who know what they are talking about saying opposite things:

-"Lap the valves to ensure a proper valve seal" , and lapping is mentioned in the manual.

-"Lapping...only exaggerates an undesirable effect"

Are these opinions open to question? Is there an accepted, repeatable correct procedure? What's a mechanic to do?

[Yard Dogg]

It's just going to depend on how much the valves and seats are worn. When I tore my motor down, I found that my valves and seats were good, there was a tiny bit of pitting, but I didn't want to lap them cause the valves were so nice, so I left it. I've always been told that valve lapping is short term maintenance that one would do during a ring job. A.K.A 50,000 mile rebuild. If the valves and seats still look fairly good, then lapping would be alright. I think you can lap them 1-2 times before they need to be cut.

[crazy steve]

Well, now we have what we often get here, different guys who know what they are talking about saying opposite things:

-"Lap the valves to ensure a proper valve seal" , and lapping is mentioned in the manual.

-"Lapping...only exaggerates an undesirable effect"

Are these opinions open to question? Is there an accepted, repeatable correct procedure? What's a mechanic to do?

There really isn't any 'right' answer. Yes, ideally you would grind/cut the valves and seats each time, but you need a machinist that knows what he's doing. You'll also run into the problem that too much cutting on the seats (not that big a deal on a OHV motor, but definitely a big deal on a shim/bucket valve train) will leave you with the inability to properly adjust the valves unless you can custom grind your own shims. These heads don't appear to have replaceable seats, so you've trashed the head. You've also got the issue of discontinued valves (for the '80-81 bikes) and whether or not you can find replacements. And the '78-79 valves aren't cheap....

The FSM gives all the specs for the valves and seats, so you'll have to look at what you have and make a judgement call. If you're close to spec, lapping will be fine. If not, you'll have to decide if you want/need to replace parts (assuming you can find them) to get back to spec or just do a simply lap and accept the results.

So lapping, while maybe not always the 'best' solution, can be 'acceptable' under some circumstances.

[Yard Dogg]

All these irreplaceable parts makes me want a Harley.

[CaptonZap]

One thing that hasn't been mentioned, but is of importance, is that lapping compound comes in various grades.
The stuff that I got at Auto Zone was, to draw an analogy, like 60 grit sand paper, when you are trying to smooth up some runs in your paint, and 400 grit was needed.
The coarser grit leaves bigger grooves, and a rougher surface, which does not promote good sealing.

Clover has a wide selection of grades, and I would look for 320 grit or finer.
If the package you find does not have the grit size on it, you are taking a chance on getting something that will do more harm than good. IMHO.
NAPA would probably be a better place to look for some, since they cater to professional mechanics, and have people who are not straight out of high school.

CZ

[GLoweVA]

Wow, I wasn't expecting this much response from my thread.
I wish I had a compressor so I could do a leak down test, but alas, I do not.
I've been working all weekend, so I haven't had a chance to even put some solvent in the ports to see if the valves even leak by or not.
Plus I've got to order me a head gasket before I get ready to do anything.

[650mark]

head gasket...

fwiw, i replaced the head gasket on my sr500 last year and used an aftermarket one recommended by an sr500 "guru". that gasket failed after about 200 miles and it cost me $400 to repair the damage. i rebuilt the motor using oem yamaha parts and no more problem. cheap gasket$15.00 oem yamaha gasket $40.00. shoulda known better, lesson learned. of course, ymmv.

[ViperRon]

The important issue is to understand what you are trying to achieve and the consequences of doing things improperly. Machine shops vary in quality and knowledge. These bikes are different from many others out there and run best if specifications are followed. Some machine shops either do not understand or do not care either way you need someone who will do it by the book if they are going to grind the angle on the valve and seat. The valves for this bike go threw a heat treatment tempering process that only tempers slightly into the metal. How far is really a mistery but you have little there to remove and still have a solid valve. If you grind the valves the seats should be done also. Old against new almost always ensures bad results. Even when valves and seats are ground some will still do a slight lapping to build a perfect seal. Lapping polishes off imperfections some small pitting and creates a surface that will wear and polish smoothly together. The more surface of the valve that contacts the seat the more heat that is dissipated. In lapping that is why you look to get the correct thickness of the band arround I think its an 1/8th. The smoother the surface the better flow and performance. The other issue is the smoother the surface the less chance of carbon hanging or building up. Carbon build up can cause pits in valves and seats and long term will prevent the valve from seating well and can cause the valve to warp or burn.

Unless you really get the wrong grit lapping compound hand lapping valves will wear your arms out long before you damage your head. For anyone doing a rebuild its one of the safer procedures for a novice to do. Now I will mention that you need to really keep track of which valve went into which cylinder or you will possibly be working way harder on the laping than you would have needed to.

Before you even start you should move the valve back and forth and rotate the valve feeling for bind or looseness. If a valve or guide is worn badly your efforts may not gain you much. If it sticks there is either carbon or a bend. Fix this before you do all the other work. The machine shop may not even look for these things but I'd hope they catch a bent valve before grinding.

As Steve also mentioned you only grind so far before you can not find a shim then you either get a new head or valves and seats all increasingly hard to get.

Remember if the shop makes a mistake you will not know till you get it together. Their answer will almost assuredly be well it was bad messed up when we got it and thats the best we could do. The cheaper shop is not always the better choice and be ware of those people in shops that want to do you a favor cause some really just want to do you.

Hope this helps some here I made it as simple as I can.

[TopCatGr58]

Hey George,

Geez...dude, I've tried to hint that you just need to ask me regarding tools or such that you may need to use/borrow! I've got a spare 4 gallon pancake compressor that you're more than welcome to borrow.

Secondly regarding the lapping compound....I used the Permatex brand "Valve Grinding Compound", their part # 80036, 34A 1.5 oz version. Note it says "Grinding" compound, not just lapping compound! And I have essentially a whole tube of this still!

Here's a quote from the Tech Data Sheet regarding this product!

Permatex Valve Grinding Compound is an odorless grey
paste containing selected abrasive grits dispersed in a waterbase,
non-corrosive binder composed of gelling agents,
lubricants, preservatives and ethylene glycol. It is a multipurpose
compound designed to aid valve grinding operations
on automotive, industrial and marine engines. Can be used
for lapping and grinding chromium-cobalt, hard-faced seats
and discs. Removes burrs, surface defects, gums, carbon
deposits and corrosion. Mixes with water to form easy-to-use
paste. Combines special grits of various sizes that become
finer as the compound is worked. Provides a fine, smooth
finish.

Here's their website link for this product.

http://www.permatex.com/products/pro...ompound-detail

T.C.

[CaptonZap]

Yep TC, thats the stuff I tried. On a 2 inch valve for a big honkin V8, it might work. It was way to coarse for valves the size of ours, IMHO.
To each his own.

CZ

[TopCatGr58]

Hey again CZ,

Well, I don't know what to tell you? I used it for redoing my head after it had some 50K miles. As it says, as I worked with it, the stuff would grind finer and finer...I would start spinning and could feel the courseness but as I repeatedly spun the valve, it would get smoother and smoother until I wouldn't feel any grinding feeling. I would then lift it up to allow it to pull more fresh compound into the interface and would spin it again with the same process. I ended up with nice 1/8" wide smooth grey lines all the way around the valves and seats, and obtained 180 psi across all 4 after the top-end breakin. It's been running great for 10+ years, so I guess I did something right? 2 were NEW valves to replace bent ones, the other 6 were the OEM's with the aforementioned 50k miles wear. No severe pitting at all on them.

As we like to say....YMMV! T.C.

[GLoweVA]

Hey George,

Geez...dude, I've tried to hint that you just need to ask me regarding tools or such that you may need to use/borrow! I've got a spare 4 gallon pancake compressor that you're more than welcome to borrow.

T.C.

TC, thanks again for the offer.
I wish I wasn't working so much. I have one had a day off in the last 3 weeks.
With the 'honey do' list, there isn't much time to play with the bike.
This weekend may be open for both days. (we'll see)
I'm just thankful that she still starts when it's time to go to (come home from) work.
I'm currently getting about 28-29MPG which isn't too bad, but it is a little hassle with the 3.9Gal SG tank and my 30 mile one way commute.
I get about 1.5 trips and then it's time to fill it up again.
Once I get this thing figured out, I should be getting about 35ish (MPG) and then I can get 2 full round trips outta each tank (120miles)

She is a decent solid bike, the rest of her is in good shape, just this issue with the compression/tuning.

[DGXSER]

George. I am almost certain it is more tuning than compression oriented. My SH compression readings are all around 100 PSI give or take less than 10%. I get anywhere from 34-40 MPG out of the bike. YMMV...literally.

[Yard Dogg]

Yeah, I was gonna say, you should be able to get 35 - 40 mpg if tuned right. I got 40 MPG religiously on my old Midnight. When I rode my XJ for the first time, I got 28MPG, but I was missing 5th gear and it was quick tuned just to get to state patrol.