question about cylinder head studs

[blackduc98]

I have a question about cylinder head studs (bike is a 97 kdx200). I just pulled my top end apart and removed the studs in preparation for sending the cylinder to be re-plated. My question is: are the studs tapered? Or maybe the threads in the cylinder are tapered? I am asking because if I try putting a nut on the part of the stud which normally screws into the cylinder, the nut only goes 2 turns before it stops. So I can only think of 3 possibilities:
(a) the stud's bottom half is tapered
(b) the threads on the bottom of the stud are slightly different pitch from top half
(c) stud got stretched

Someone enlighten me please. A companion question is: after my cylinder is re-plated, how do I clean up the threads? Can I just use a normal tap, and of so, what size? Also, is it OK to reuse old studs?

 

[canyncarvr]

(d) Wrong nut?


A tapered thread (say...pipe) would show up some past a thread or two. Consider: If it DID taper that fast, how is it going to make it all the way INto the cylinder? Well, obviously with a tapered thread there, too..but I don't think so.

It's listed as an 8x32 stud. I've not actually checked mine..but I believe they are not taper threaded.

I have a spare cylinder at home. I'll check one of mine if you're interested.

Shouldn't be any clean-up necessary. Those areas of the cylinder should be well protected during the plating process.

re: Reuse?

For the $2 they cost, I'd replace 'em. No particular reason. There shouldn't be a big stretch problem with the 18ft/lb they get twisted to.

Still, I've heard of other's bad luck with them breaking at that torque..which is why I wouldn't bother putting in the old ones.

FWIW..Mr. Fredette reuses them. He did on my cylinder, anyway. Well...I recall there was one new one. Don't know why. Maybe it broke! :ohmy:

Who's doing the replate?

 

[blackduc98]

(d) Wrong nut?

I tried it with the same nut that came off the stud's other end. Is it supposed to fit on both ends? I assumed that both ends would have the same size threads. The nut threads easily onto the stud half which goes thru the head (which is what you'd expect of course). But not so on the portion of the stud that threads into cylinder. Maybe it would thread easily if the stud was brand new?

A tapered thread (say...pipe) would show up some past a thread or two. Consider: If it DID taper that fast, how is it going to make it all the way INto the cylinder? Well, obviously with a tapered thread there, too..but I don't think so.

You may very well be right, i.e. it is not tapered. Perhaps the threads got stretched just a little? My street bike (early model air-cooled ducati 900ss) is well known for breaking head studs, and the explanation I've heard was that the stud breaks because the aluminum head expands considerably more than the steel stud when it heats up, and eventually fatigues and snaps the stud. Ducati's remedy was to switch to a "stretchier" stud. So I'm thinking that my KDX could have stretched stud threads, and perhaps cylinder threads too. Or maybe I'm just being overly paranoid. :yikes:

It's listed as an 8x32 stud. I've not actually checked mine..but I believe they are not taper threaded.
I have a spare cylinder at home. I'll check one of mine if you're interested.

If you get a chance, that would be great.

Shouldn't be any clean-up necessary. Those areas of the cylinder should be well protected during the plating process.

I was thinking about cleaning up leftover loctite or whatever the hell it was that made it so difficult to unscrew my studs.

Who's doing the replate?

I plan to send it directly to US Chrome, but I'm open to other recommendations.

 

[canyncarvr]

Sorry...I didn't keep track of this thread.

The studs are the same thread pitch on both ends. I took a spare stud of mine and threaded a nut to the end of the threads on both ends using my fingers.

You can remove loctite residue with a wire brush. I'm sure some solvent or other will work, but I don't recall which type.

Anecdotal info is not the best to count on..and that's what this is: My experience with USC isn't good. I know of other riders that have had a similar bad experience with them. I don't know from personal use who I'd prefer, but I won't ever use USC again.

I've heard good things about Langcourt. That's where my cylinder is going next time (to hopefully fix the USC mess!).

Good luck!!

 

[blackduc98]

replating (was: studs)

Sorry...I didn't keep track of this thread.
The studs are the same thread pitch on both ends. I took a spare stud of mine and threaded a nut to the end of the threads on both ends using my fingers.

No problem. Thanks for the update.

Anecdotal info is not the best to count on..and that's what this is: My experience with USC isn't good. I know of other riders that have had a similar bad experience with them. I don't know from personal use who I'd prefer, but I won't ever use USC again.

Ouch! That info comes a bit late since my cylinder is already at USC. But since this is the first time I've had anything re-plated, I'd appreciate if you could share the nature of your problem, i.e. what should I look out for?

 

[canyncarvr]

USC's point of view: Some cylinder base material is quite porous. Replating leaves pits. Some pits are OK.

They will send you a piece of paper with a lot of specks on it attempting to define the criteria used to determine if the cylinder is good enough...or not. If you don't get that 'documentation', tell them to send it to you.

Sort of like bad pixels on a digital screen..the number of bad pixels AND where they are (Right in the center? Off to the side?) are applied to the criteria to determine 'good screen' or 'bad screen'.

My cylinder came back full of holes. USC thinks it is OK. I do not. A local rebuilder wanted to know who did the work on my cylinder, 'I want to make sure I NEVER send anything to THEM!' he said.

I haven't checked...but there may well be different sites for USC operations. If so, one is not necessarily like all the others.

Plating material can be built up to quite a large thickness (says Langcourt). So.....plate it thick enough to cover the holes, then hone the thing out to the correct bore size!

My opinion matters not a whit, I'm sure. I'm not a metulurgist, neither. Still, I'm stuck with a cylinder that has some serious problems..and it is related to USC's replate. I'm less than happy with USC.

...I said that already.


Good luck! I hope you don't need it!!

 

[blackduc98]

received my replated cylinder from USChrome

USC's point of view: Some cylinder base material is quite porous. Replating leaves pits. Some pits are OK.

They will send you a piece of paper with a lot of specks on it attempting to define the criteria used to determine if the cylinder is good enough...or not. If you don't get that 'documentation', tell them to send it to you.

I received my cylinder from USC today. They did not include the piece of paper that you're talking about. I can see just a few pits but not with a naked eye - I have to use a magnifying glass and put my nose right inside the cylinder bore to see them. They look insignificant in size, and few and far between, but I really have no standard to compare to.

What does upset me is that there are a couple of small gouges near the top of the bore. click HERE for pic. The bottom gouge seems to be at the same "altitude" as the top piston ring, though I won't know for sure until I install everything sans the cyl head and measure it. I really don't want to send it back for repair :( so I hope it is above the top ring.


Gasket matching surfaces (click HERE for pic.) are very rough (probably from the chemical strip bath) so I'm planning to polish it with 600-grit sandpaper on a glass plate, which should be easy enough for the head gasket flange, but the base gasket will not be so easy since the cylinder skirt sticks out beyond the base gasket surface. Do you think I can cheat and just use gasket sealer on the base gasket instead of trying to polish it?

BTW, there was a $14 energy surcharge which came as a surprise, but it was my own fault for not paying attention to the small print on USC's pricing web page (it says at the bottom that a 5% energy surcharge will be applied). I'm not complaining about this - I'm just pointing this out so other folks don't get surprised. However, the way $14 was calculated irks me a bit: my bill breaks down like this:
$165 for strip, replate, and hone
$121 for wiseco piston
-------
$ 286 total

$14 is equal to 5% of $286. Seems to me that 5% should only be applied to $165, i.e. why should I pay an energy surcharge on the piston? I'm not going to worry about this unless I have to call USC regarding the gouged bore, in which case I'll ask them about their surcharge logic too.

 

[blackduc98]

Oops, forgot to update this thread. I called USChrome about the gouges. Their response was "That cylinder should have never left our shop. Our inspector should have caught it and the cylinder should have been re-done. We'll have UPS pick it up asap." USC also told me that if I wanted to, I could go ahead and install the cylinder as is, and if there are any problems then I could have it repaired under their standard 1-year warranty. Sounds fair to me.

 

[Rhein]

so any problems since then?

 

[blackduc98]

Problems? None that I could attribute to the cylinder :-)
I put the motor back together and it seems to be running fine. I used copper-cote on the head gasket because I didn't like the rough gasket matching surface that resulted from strip/replate process. Compression is 150 psi when the engine is cold, and it pulls strong - just twist the throttle and the front wheel lifts into the air in 1st and 2nd gear with 13/49 sprockets. So now I'm learning the fine points of carb jetting, and of riding this bike in tight New England woods. One caveat: I am fairly new to off-road riding, so I don't rev the snot out of this motor. YMMV