Getting to the cam Valves

[nickr234]

So yea, I really messed up guys and I need probably all the help I can get.


I have a 1978 gs 750 and when I was doing a plug check on my 1st (left most) cylinder and I somehow cross threaded it on the way out.


To remedy this I bought a heli-coil kit and started to go to work. Since the whole thing was striped I had to tap the hole all of the way in. and of course I started at TDC so wouldn't hit the valves. But the cylinder head wouldn't let me go all the way in so I slowly turned the timing adjuster nut to turn the engine forward to let the piston down so I could tap it the rest of the way, this is were my troubles started, as turned the timing bolt forward it lurched forward just a little bit and it was enough for the valve to strike the tap (unknown to me at the time). I then taped the hole the rest of the way and took the tap out to see the intake valve have a nice little chunk taken out of it yay!!


So here is what I am thinking I am of course going to need to take the top end off and take the valve out and replace it. But here is the trouble. The factory manual doesn't really have that good of graphics and it doesn't show how to take the cam chain and cam rollers out. And I am wondering how to do that. I haven't torn the engine apart yet, and am considering taking it to a mechanic, but I kinda want to fix my mistake myself because I feel horrible about it (actually just really stupid) and I feel like it would be a good learning experience to take the top end off.


Can you guys give me some advice as to what to do. I'm going out of my mind a little bit right now lol.


Thanks in advance

[Big T]

Well, that will cost you a few hundred in gaskets , at least

Use factory gaskets and tear it down to the cases, because you'll probably create a leak at the base gasket when you pull the head off

You don't remove the cam chain, you pull the cams out from underneath it. Attach a length of wire so you can retrieve it later

Likewise, the cam guides don't come out as such. The front one just slides in, the rear is bolted on. You'll want to consider replacing them because they age and get hard

Just follow the

Carb removal
Cam removal
Head removal
Cylinder removal

in the FSM and you'll be fine. If you get hung up, ask here. Take pictures as you disassemble and lay out or bag the subassemblies as you remove them

You'll also want to consider:

1, A threadsert to really fix that plug hole
2. Refurbing the camchain tensioner (see BassCliff)
3. Refurbing the tach drive (ditto)

Just to save yourself time later on. A good learning experience indeed

[nickr234]

So here is what i am thinking.

I got all of the gaskets on their way (top cover, head and base). I am also going to buy a "NEW" head and will seriously consider just replacing the head with the one that i buy so i don’t have to deal with the thread-sert. Also i will just not risk the chance of having that bite me in the butt on a long ride if I don’t do it correctly. That head with give me a good practice for when I actually get to the real deal (the head comes along with everything included except the cam rollers). And it will also be a good test to make sure I get the right tools for the job.

Also if I take out all of the valves from the "new" head and replace them with the ones on my bike will I have to reshim them still? I do know that no matter what I will have to reshim the damaged one.

I am getting a little excited here and I think I will be able to do this I just need to take my time and not rush anything.

If you have any more pointers I would greatly appreciate it.

Thank you,

Nicholas

[Big T]

You'll probably need a few more gaskets and such

You'll need the square O ring between the head and block (#8)

Fresh valve stem seals are a good idea

The ovoid O rings under the block (#6) are a must

The O rings and gaskets for the cam chain tensioner and tach drive would be smart

You don't want to go swapping valves between heads unless it's necessary, or you bought new valves for the "old" head

You'll want to pull the valves out, check their seal, seats, tightness to valve stems and refresh the valve stem seals at a minimum. If they look good, or fair, a quick spin with lapping compound and you're good to go

What ever you do, checking the valve clearances when you're done is mandatory

[nickr234]

You don't want to go swapping valves between heads unless it's necessary, or you bought new valves for the "old" head

Why is that? Does it have something to do with how everything wears down together?

Also in your honest opinion how much of a chance do i have of skrewing this up if i have never done this before? (im still going to try no matter the answer)

Thanks again,

Nicholas

[Big T]

You really need to cut new seats for a new valve, so yes, it is sort of like parts mating

It's not really a hard job, but patience is a virtue

[Suzuki_Don]

Hardest part of this task is removing/reinstalling the valves (deep inside the head) you will need special valve spring compressor or make an adapter, also fitting the cylinders back on the pistons without breaking the rings.

[nickr234]

one last question. can i take the whole Valve assembly and switch them between heads.

[TheCafeKid]

Not really. Here's how it's laid out.

The cams rotate via the chain. The cams have lobes that ride on top of (but not always in depressing contact with) the shims which are located on top of shim buckets. Under the shim buckets reside the valve springs. Those are held in place with a two piece retainer that is held together by the spring pressure. To remove the retainers the valve springs must be compressed with a special tool or a home made tool made from a large C clamp and some PVC pipe with a window notched in it to get at the retainers once the valve springs are compressed. Basscliff has an excellent video tutorial by Steve last I knew.
The valves ride inside valve guides which cannot be removed without a machine shop more or less, as re-installing new guides (never used) requires reaming and pressing.

Now, you CAN simply replace your dinged valve. Is it the perfect fix? No. But many have done it including myself and Steve on his sons 850 when one of his snapped in half. However, usually a GSR member will sell you a head complete with the valves and caps and etc. Unless he's an idiot, as most of us on here know the parts wear as a set, and should be sold as a set. Youre better off, IMO, buying a complete head and installing new valve seals, lapping the valves by hand since you're there, and Bobs your mothers brother.
No sense in screwing around with your bunk head with a bad sparky hole to fix one valve. Look around someone here prolly has a head they'll part with. And if you're not in a huge hurry, I know I do but it'll be a couple weeks before I can get it apart and such.

[nickr234]

Thanks, it seem when i can get my head visually around what is going on i becomes easy to understand.

I actually have a head on the way but it doesn't have the rollers with it, will that skrew anything up if i use the rollers from the "old" head. all of the vavle faces look great on it accept for one exhaust vavlve looks a little burnt. it also comes with all the skrews and clamps so if i strip something i will have back ups. also it was only about $75 with shipping. woot for ebay. also the main gaskets i got for cheap, but i had to get the smaller gaskets from a suzuki supplier.

Also were is a good place to buy that spring compressor. i know it have to be a certain size, so im guess suzuki would be the only place.

[Big T]

The face you're concerned with is not the bottom of the valve

It's the beveled one that touches the head. It needs a nice, thin line around it that confirms a good seal.

Normally, you disassemble the head to confirm the status of the valves and their seal

If by "roller" you mean the camshafts, they can be swapped from head to head with now problem

Show us some pictures once you get the new head

[Guy]

Why not keep things simple?
I'd have stuck with the original head, sorted the plug thread issue, removed all the valves and lapped them, replacing the one you damaged with a new one and put it all back together with new seals and gaskets.
Swapping valves, cams and caps between heads is not a good idea and will probly end in tears. Usually results in a noisy top end too.

[nickr234]

well, not so good.

I lapped the valves and replaced the oil seals on the new head. the vavle seats themselves didn't look too bad on the intake, but the exhaust vavle seat looked like they could be reworked, but i didn't want to pay a machine shop for it. i then put the head on.

then I reshimmed it to get it within spec. but now that i'm done and tried to ride it around and i can't get up to the top end. i am only getting a PSI of 100-90-90-90 warm. so all of them are very low. any ideas, or am i going to have to just take it apart again and go over everything to make sure i didn't miss something? i also did not take the cylinder jugs off because there was no way i distrubed the gasket on it, it was locked tight to the rest of the engine.

Do you think it might be those exhaust vavle that are coming back to haunt me?

i also started it up with no oil for about 10 seconds untill i realized that i'm an idiot and need oil. could that have made any problems?

should i do a leakdown test?

Thanks in advance

[nickr234]

well

Well so i put everything back to stock (exhaust and air box).

it was a lot better but it just wasn't the same as before. From what i have said do you think that it is those valves that are not seating correctly? or do you think that i skrewed something up with those piston rings back when i started it without oil?. there is absolutly no smoke at all so i am just kinda thinking that it is the vavles. But what do you guys think

i will also take pictures of those seats and valves next time i take it apart which will be this weekend. what do you guys think?

[TheCafeKid]

Are you following the proper procedure for testing compression?
100-90-90-90 isn't great but it also doesn't sound horrid. It also sounds like it may come up a bit after running. I doubt you did any serious damage running it for a few seconds without oil. While not advisable and definately not GOOD for it, most of those parts are so impregnated with oil at this point that a few strokes isn't the death of it. Besides if you had done damage to cylinder walls it would be smoking. I've read through this thread a bit and it's a bit jumbled.
Plus there seems to be information missing as well.
You say you put it back to stock.. Runs better but still not great. What exactly did you have or not have intake and exhaust wise to begin with? And now you have airbox and stock pipes? Did you rebuild the carbs, replace the intKe boot orings, and assure that your airbox is sealed properly and the boots fit over the carbs correctly? And what is the bike doing? I'm afraid you may be chasing your tail looking for a problem with the motor when the problem lies inthe intake system instead. The 750 8v motor was one of if not THE most bulletproof motors to roll off the Zook line. Majorly overbuilt.
Let's roll this back to the beginning and start over.
What is your current intake and exhaust set up, and what has been done to it to ensure it's sealing and breathing properly?