Rebuilding top end on a 74 z1 900?

My 2 cents.....

Lapping valves is no substitute..... If you want the most efficiency out of your motor....just bite the bullet and get the valve job done. And I agree with Jay...it's very possible it will need guides.

Having done many KZ motors over the years, I can tell you with 100% experience and confidence that a good valve job pays dividends in the way the bike responds and also in the exhaust note.

George,

I can tell from your post that you've never done a valve job on a KZ......

wiredgeorge wrote:

Hey oldkaws4ever... No one actually gave you the advice you need... DO YOU NEED NEW VALVES? To figure this out, you can do it WITHOUT removing the cylinder head. Check your valve clearances. If you need a bunch of the skinniest shims, the seats are worn and if I were installing new seats, I would replace the valves at the same time as the valves are likely tired as well. .

A leak down test will tell you how well the valves are sealing. They can seal but still be far from an optimal valve job.

Post edited by: larrycavan, at: 2007/08/07 06:02

The reason I say to replace the exhaust valve and seat is it is an old engine and you dont know for sure if you have a hardend seat to acept unleaded fuel. As for the valve replacement you would want to, FIRST you have an air cooled engine so it operates at higher temperatures. SECOND if you were to grind the valve just the slightest you are removing matterial which means less heat it will take.
As for my experience, I have done valve grinds, I have replaced valve seats and guides, I worked at a machine shop for three years part time. This does not make me a machinist or a profesional, but I can tell you for sur I know more then the average joe mechanic on this suject.
It doesnt matter if you have a bike car or truck. You face the seat based on grinding circle and thickness of the seat, and matting surface area. If it is still not within specs. you grind more till it is. The more you grind the less matterial you have and the more your placing the valve furture into the head.

Yeah Larry... that is the way you tell if you need new valves... a leakdown test. Do you think you need new valves if they aren't sealing well? If you put new valves in do they seal well automatically or do you need to lap or recut the seats? The fella was looking for info and I tried to present a little info. He was asking about how hard it was to change valves and I thought the bigger question was whether new valves are needed. If you and wireman want to jump me for giving some advice, that's OK... If the advice is wrong.

Here is a problem I see with cylinder leak down test. You also have to look at the piston sealing if it isnt then you are not getting a good reading.
You can do all the on bike test you want to but the real you is to take it apart and inspect, and measure.

Actually I have a story with this well maybe not but its a story that this tread reminded me of:
My frend had a ninga I beleave it was a 600 and he took it to people that told his valves are bad, and he got a different opinion that said piston was bad, and even another that said electrical gremlins:laugh: .
It turns out after I did my testing it was inconsistant and could not come to a conclusion. So I told him I would have to take the head off to make a decision. Turns out after I took the head off it appeared to be a mesh of some sort that filled his cylinder. It looked like some mouse or what ever built a nest in the intake and it got sucked in and would have it missfire, spit out thecarb and powersurge at WOT.

wiredgeorge wrote:

Yeah Larry... that is the way you tell if you need new valves... a leakdown test. Do you think you need new valves if they aren't sealing well? If you put new valves in do they seal well automatically or do you need to lap or recut the seats? The fella was looking for info and I tried to present a little info. He was asking about how hard it was to change valves and I thought the bigger question was whether new valves are needed. If you and wireman want to jump me for giving some advice, that's OK... If the advice is wrong.

who started jumping who about giving the wrong advice here?:whistle: its just anytime anybody else has an answer you dont like its wrong,thats why they call them opinions.Larry builds a lot of motors,youve built motors,ive built motors we all have our ways of doing things

well here is the real deal, in order to tell if you need to replace the valves the head must be taken apart and the valves checked for size along with the guides, in addition you need to grind the face of the valves and inspect them for being too thin.
Valve seats, on a bike engine, check the height of the valves to see if they are too deep in the seat both prior to and after grinding them, this is done with a height guage.
and by the way, I spent about ten years in the automotive machine shop buisness,

George,

There are two ways of doing things. The cheap way and the right way. The cheap way generally costs more in the end....Taking it apart the second time adds up....I've seen it a thousand times.

The valve seats are not something you replace simpley because the head needs a valve job. You might be amazed at how much seat material there is to work with.

In fact, when installing the common 37.5 / 31 oversize valve combo in one of those heads, you have to sink the valves a bunch.

Replacing valve seats in a KZ is not the norm...unless you were installing very big valves for drag racing.

Now let's approach the shims being on the thin side. If the valves have never been tipped, it probably won't matter at all. You have stem material to work with to ge the shims back up to say 240ish range.

"Don't try to describe the ocean if you've never seen it" ----Mr. Jimmy Buffet







wiredgeorge wrote:

Yeah Larry... that is the way you tell if you need new valves... a leakdown test. Do you think you need new valves if they aren't sealing well? If you put new valves in do they seal well automatically or do you need to lap or recut the seats? The fella was looking for info and I tried to present a little info. He was asking about how hard it was to change valves and I thought the bigger question was whether new valves are needed. If you and wireman want to jump me for giving some advice, that's OK... If the advice is wrong.

Post edited by: larrycavan, at: 2007/08/07 19:08

Larry I am not sure where you are going with this, but the question was to replace valves, nothing about over size, but either way, if he is going to do a top end, then yes take it apart, check the valves and seats and guides, it is of good opinion that with that few miles things will be in good condition, and replacing the seals will be in order.
One thing to think about is how the bike was cared for, could be it was run hard and parts are damamged,or it is in great condition, only time will tell

Larry has said all the right things about a leakdown... the issue got off to the wrong foot because I think fundamentally, the wrong question was asked... I think it was "how hard is it to change out the valves"... or something along those lines. I pointed out that the easiest way to get a hint if new valves are needed is by shim size... this would indicate valve and seat wear. If the shims are still relative thick... that is over 250 or so, I doubt that new valves are an issue.

The better question would be, "I am going to freshen my 18K mile engine, what do I need to do with the top end?" In this case, a leakdown test would be the first thing I would do if giving an estimate for work... I would know how the valves were sealing. I can't imagine the original poster has a leakdown tester and will probably take off the cylinder head anyway to dig around.

This being the case, the most likely thing needed will be to check the valve guides which will probably be OK at this mileage and to de-carbon and lap and install new seals. He should probably check the seal using machinists dye which gives a great indication of the seal when the head is off the bike. He should also check valve length to ensure the valves are in spec and if the engine is a 1000, I think the valve springs have a compression spec... I don't think the 900 springs have a spec for compression, only overall length.

I guess a better way of addressing this question originally would have been to point out that the issue was not being addressed with the right initial question... hope that came across more clearly. I hope he doesn't ask about the block and pistons! bwhahaha

I tried to point out that there is no need to worry about having to replace valve seats on that head....That's the thing in the post that caught my attention and why I commented on it.

I've never in over 25 years of working on these things, seen a head with 18,000 miles that couldn't use a valve job. I've also never seen one that needed valve seats replaced unless it was "racing related".


Generally, unless they are bent, The valves can be refaced and reused. Guides are hit and miss. The later cast iron guides are IMO better than the early head bronze guides.

I'm pretty set in my ways about valve jobs because they do make a difference. It is IMO the right way to do it. Taking the time to pull the head, maybe re-ring the pistons and not do a valve job is just wrong IMO. :sick:

90% of the time, it's guides, valve job, seals and resurface....out the door.

George is right...the question should have been put differently....it was a bit open ended...thus the varying opinions...no harm done...everyone is right to a degree.

I developed a certain method of doing things that I just don't stray from. If you're doing this for someone and getting paid, you leave nothing to chance. That's been my method for so long now, I just do it without thinking about it.

I never agree with cutting a corner to save $100 for anyone. If they don't have the money to do it "my way", and I still agree to do the work for them, then the full system gets applied regardless of the price.

Look at it this way. Use everything you know in everything you do and you'll seldom go wrong....



PS...speaking of valves. Stay away from those JUNK OEM replacement valves that seem to be coming from China or somewhere where they make inferior junk. They are horrible.

I had a guy bring me a head and 4 brand new OEM replacement valves. I put them in my valve machine and not a one of the valve faces was anywhere near straight. I refaced one to try to salvage it...total crap. I gave him 4 used KZ1000 36mm intake valves that I refaced....they worked just fine. He was going to ship the junk valves back to where he bought them.

Be Aware of that..

Post edited by: larrycavan, at: 2007/08/08 20:00

what is a good source for good stock replacement valves,not stainless?