gy6 valve guide replacement?

[xlint89]

As some of you may know, I floated my valves when over-revving and bent both valves on my GY6 150 howhitt engine.

The intake is only slightly bent. I think it's from contacting the bent exhaust valve. But the exhaust valve is WAYYY bent. And because of that, it egg-shaped the valve guide opening in my NCY ported head.

How difficult is it to replace a valve guide in these heads, or is it easier and just as costly to just replace the head? Thanks

[toomanytoys2]

It really isn't that hard. I have never done a GY6, but have done many on the air cooled VWs and the procedure is the same. To get the guides out, you need to heat the head, then drive them out. To install the guides, You put the guides in the freezer and get them nice and cold. Then you heat the head and drive them in. However, after you drive in the guides, you have to run a reamer through them. The guides usually get a little distorted after they are driven in. The reamer brings them back to the correct diameter.

So the process is really not too hard, but you may have a difficult time locating the guides and reamer.

Good luck.

[xlint89]

Thanks for the response.

[ckau]

Originally Posted by toomanytoys2

So the process is really not too hard, but you may have a difficult time locating the guides and reamer.

Good luck.

with all my veiwing of scooter and gy6 asociated parts sites, I don't recall ever seeing just the guides and/or a reamer offered. I 'm sure they can be had but it will take some persistant searching to find them.
Any idea of how high you were turning or what caused the snafu?

[xlint89]

I thought I saw some guides listed somewhere, but after talking to Tom from Syc Powersports, he was sure he would be able to help me source a giude or 2, even from a good used head if need be. (really good guy)


As far as the RPM, I would have to say somewhere around 9k. I don't have a tach mounted up, but can tell you she was SCREAMING.... And yet I still kept my foot into it.

It really happened after a short sustained run of high RPM, it didn't just reach high RPM and go. It was me ultimately murdering it that led to it's demise.

[xlint89]

Here you go.

http://www.bing.com/images/search?q=...48514&first=39

[xlint89]

Well, it really was easy to do.

Got a new valve guide from ******** for around $6. However the valve opening was too small.

Bought a #9 drill bit and drilled it out for a perfect fit.

Used a SS allen head bolt and drove the old guide out. Lubed up the new one, installed the seal and drove the new one in.

That was it.

Thanks for the tips and the offer of the valve guide Tom.

[Johnny 5]

What cam were you using and what rear sprocket.
I am thinking of of getting titanium valve retainers from scooter elements for 45 bucks.
The A12 cam has way more lift than stock and I am concerned about bending valves.
Did your ncy head have heavy valve springs?
I thought the stiff springs would prevent valve float.
That is cool that you were able to save your cylinder head.

Check out on you tube camshafts at 14,000 rpm.

[xlint89]

I was using the A11 cam. I read a few posts that said the A11 comes really close to the valve and you have to pay close attention to cleaerance with it. (you should with all cam replacements, but especially with the A11)

I have 13/42 internal gears with a 39 tooth axle sprocket and 16T engine sprocket on the reverse gearbox. (have now gone to a 36T axle sprocket. So far it seems to be doing well, but I haven't opened her up too much yet since I'm seating new piston rings)

Weight savings and strength on the valve train is always a good thing.

I don't think the A12 has as much of an issue as the A11 as far as valve contact. It's not always just the height of the cam lobe, but also the "timing" of it. The piston chases the exhaust valve closed, that's why it "floating" can be disasterous. The A12 may start to close the exh valve sooner than the A11, and may be why it isn't as much of a concern.

My head didn't have any different springs than what came with it as far as I'm aware. The NCY 14,000 RPM springs aren't much better than stock from what I've been told. Taida springs claim to be better than the NCY, but who knows??? (although I did replace mine with the Taida springs) Tom at Syc powersports gets his performance valve springs from a company that makes them in the U.S. They are quite a bit pricier, but those are the ones he runs. And from my dealings with him, he doesn't use "junk".

Stiffer springs do help prevent valve float. But too stiff will also add wear and tear on other components as well. You'll have faster wear of the cam, rocker arms, and most likely stretch the timing chain faster too. It's a balancing act if you will. Just enough pressure to close the valves, but no too much in order to promote longevity.

The best thing to do is keep your RPM down where float isn't a problem.

Drag race vehicles turn really high RPM to make high HP.

Off road vehicles and trucks that pull heavy loads tend to turn much lower RPM and concentrate on the TQ an engine puts out.

If you set up your buggy to run in your engine's TQ peak RPM range, I doubt you'll have to worry about ever bending a valve. And it will have all the power to take you up a steep hill.

Now if you want to drag race your buggy, then you WILL need the stiffer springs and titanium retainers, plus the A12 prob isn't the best choice for you either. You'd want a A9 or something like that.

Hope this helps