Valve lapping ?

[GLoweVA]

Okay, I've finally got enough motivation to go ahead and lap the valves on my SG.
I swapped the heads with my G a couple months ago, so the SG head is sitting on the carport floor.
(the reason why I swapped heads was because I have a low compression problem on the SG (#1,2) and I thought it was the head/valves, but it might be a bad head gasket. I don't think it's the rings because the compression numbers didn't change much after adding some oil in the spark hole)

I've been reading up as much as I can find on lapping.
I guess the first thing I should check is: to fill the intake (and exhaust) ports with some 'solvent' and see if the valves even leak by or not.
When I first got the bike, #3 exhuast valve was bent, so I got a new one in there, but didn't bother to check to see if it seated 100%.

So, with the G's head on the SG, I still have poor starting and marginal performance. (like before)
Okay, I'll order a new head gasket. (anyone know where to get one for a good price)

[TopCatGr58]

Hey George,

Glad to see you're not frozen YET! You have my sympathies having to drudge it out there commuting! You haven't come by to get the Lapping Tool and Lapping compound either!

Okay, the OEM head gasket is rediculously expensive, and so most folks just order the complete aftermarket kit from Partsnmore.com, it runs about $80.00 or so, but you get an entire gasket and valve seals kit....I paid like $8.00 ea for my valve seals in 2000 when I did my topend....not knowing about the Gasket Set!

I also think folks reported finding the kits on eBay as well as some other sources, and that the gaskets were being made by a japanese company so that they were considered good quality!

T.C.

[GLoweVA]

Yeah TC, it's been cold alright!
Thru most of Jan, I had the sickness and with the cold, I haven't been riding her to work. (taking the cage instead) (just started riding her again)
I do need to swing by and borrow that lapping tool, thanks for the offer.
A few years ago I did get the complete gasket kit for the G when I did the piston replacement, but only used the valve cover and head gaskets out of it.
I think all I want to get is just the head gasket. Cometic makes one for about $50 that I've seen online.
I think I read somewhere on here once about members 'refurbishing' their head gaskets. Is that even possible?


I wish I had a garage or it wasn't so cold out, plus I could use a few days off, been working at least 6 days a week trying to get this latest US Navy submarine delivered. Looks like the work schedule won't let up until April/May. That's great for the wallet, but not so for time for working on the bike.

[MaximPhil]

Hi George,
Gasket manufacturers will tell you gaskets are single use only. What it really comes down to is risk management. Fequently a soft material gasket such as the valve cover will work a second or even a third time if it is not visibly damaged. It is easy enough to do over when it leaks oil on your jeans so not high risk. Cyliner head gaskets on the other hand are multi part metal clad gaskets working under much greater pressure. Less likely to work a second time. Engine suffers if it fails and much more difficult to replace therefore much higher risk to not replace it.

I would replace the valve seals, which came in the kit you have, and also use new Exhaust gaskets although easy enough to replace it is in my opinion better to do it all at once. How is the camchain while you are in there and ordering parts May as well spend next weeks grocery money
Phil

[GLoweVA]

Thanks Phil, I do like the idea of replacing the valve seals if I end up lapping them. Heck the valve is already out, so why not, especially if I already have them in the gasket kit.

(I just got to check to see if I actually got to lap them or not)

As far as re-use, I've gotten away with re-using my head gasket on my G before and it seemed okay and didn't fail, but that didn't seem to be the case on the SG. (I guess from now on, everytime the head comes off, a new gasket is going on!) (got to order 2 now)

I used the exhaust gaskets out of the kit already for the G's 'header project' that TC did for me.

The SG has low milage on her, so I figure most of the other gaskets should be good. (heck, even the old valve cover gasket came off in one piece)

[natemoen]

Really it isn't a question about if the valves need lapping or not, just do it. If you have never done it on your valves just do it, can't hurt anything. Just make sure to clean all the lapping compound out after.

[Yard Dogg]

When it comes to valves, I only depend on lapping if there is minimal wear. If they are worn out badly, it's worth it to pay a machine shop to cut them, and seat them. I say that because the valve seats are cut at a different angle than the valves, and there is only a small surface area that the valve contacts the seat. If you lap them, the valve will end up with a groove where the seat is and loose compression faster than if the valve was machine cut. If you have a shop do the work, then have them shim your valve springs while in there to get the right valve spring tension too.

[CaptonZap]

Years ago, when I dealt with small engines, Briggs, Clinton, et al, if the head gasket came off clean, (I didn't have to scrape or pry it off,) I was taught that a THICK coat of high temperature silver or gold paint, applied to both surfaces, and then torqued religiously, would do, if you could not find a replacement gasket.
Later, when I ran with the stock car racers, who seemed to take the heads off weekly, I found that they would use the gaskets more than once, using the same procedure. (These were low bucks claimer racers. Strange, but it seems that stock engines, revved a thousand or so past their design limits, had a habit of destroying valve train components, if not more vital engine parts.).

With that said, I agree with the advice to replace it, if you have any doubts.
If money is an issue, a can of paint is cheap, and a re-torque of the head after a good warm up and a few mild miles on the engine might get you through. CZ

[Yard Dogg]

Don't forget you can make copper head gaskets too.

[GLoweVA]

Don't forget you can make copper head gaskets too.

Yeah Dogg, I forgot about that. But with the price of copper today....

[MPittma100]

Valve lapping

Well, it would seem as if the problem with the engine may or may not be with the head. And I am basing this on your statement that nothing much changed as a result of changing them out. This suggests that changing parts out may not be the best approach this problem.

Your best diagnosis will come from a cylinder leakage test before taking the head off. You are allowed 15%. Any more and there is a problem. The possibilities for the leak, if you have one, are either or both vales, rings, or head gasket.

If there is a valve(s) leaking, the best route for repair is to take either head (preferrably the original one to the engine) to your local machine shop and have them make the repair. Take the cams with you and they can adjust the valves so you want have to go through the shim dilemna afterwards.

Lapping valves is something you do after they are ground. Lapping alone will not stop a valve from leaking.

My 2 cents.

MP

[CaptonZap]

If there is a valve(s) leaking, the best route for repair is to take either head (preferrably the original one to the engine) to your local machine shop and have them make the repair. Take the cams with you and they can adjust the valves so you won't have to go through the shim dilemna afterwards.

Lapping valves is something you do after they are ground. Lapping alone will not stop a valve from leaking.

My 2 cents.

MP

If you do take the head to a machine shop, for valve grinding, and setting the valves, BE SURE to tell them that this is an interference engine, other wise they may bend a valve by setting the head on a flat surface while adjusting the valve clearance, or rotating one cam without rotating the other the same amount.
And they won't know where to get more valves.

The cams MUST be in the proper relationship to each other as they are BOTH rotated, and the head must be elevated from the table, so that the valves do not hit the table as the cams are rotated.
Another 2 cents worth of opinion, CZ

[MaximPhil]

Having read this forum for many years I have heard the horror stories of people having professional mechanic adjust the timing and ending up with bent valves. I am therefore baffeled at the suggestion ANY and Every Machine Shop would have the skill to do a good job OFF the bike in ONE shot getting it right when I have seen experienced XSives who knew what they were doing have multiple goes to get the timing just right.

Just saying
Phil

[TopCatGr58]

Hey George,

I didn't get to reply earlier, COMETIC makes the gaskets that are used with the Wiseco Big Bore kits, that's what I put on Godzilla when I did the rebuild.

I also bent a couple of valves by accident/ignorance as has been stated by others, both cams in at the same time...DOH! When I put the replacement valve in I did NOT grind it, because it was made for the bike/engine and I "assumed" that it was shaped properly to begin with. SO...I just lapped it in and was able to obtain the same 1/16th or 1/8th" gray line all the way around the valve and valve seat. It's been over 10 years, and it's been holding up great with over 16K miles. I also lapped all of the other valves/seats as well.

Tod/Trbig has also posted about having re-used the head gaskets many times without ill effects. I can understand the use of copper paint to put a few thousandths of extra compressible thickness..not exactly the same as annealing copper compression washers.

T.C.

[DGXSER]

honestly, if you are trying to achieve a "new" engine for one of these bikes, or building a megga horsepower machine out of one, I would go to the extent of having the valve seats machined. Honestly though, the money you will spend having the valve seats ground will exceed what I have paid for 2 of 3 of these bikes.

Now, this is not to say that machining is a bad thing to do, just way overkill IMHO. Lapping the valves in these engines will produce the desired effect. Seen it, done it. Dbeardslee and I did a couple heads a few years back.