Fitting new valves and guides

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cmattina
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Fitting new valves and guides

Postby cmattina » Mon Oct 19, 2020 9:36 pm

Hi all.

This is sort of a general question that may not be specific to Ariel, but may be specific to engines of our sort. Mine is 50 NH350

I bought the bike as a basket case and got around to the head last night. There were little holes in the guides, when i installed them, I had them both facing "up" or toward each other - was that right? I thought they were for oil or something, so i thought if they were facing up, gravity would take the oil down.

Secondly, the new valves were a tight fit, to say the least... I would say in a perfect world i would have the new guides reamed. But... i'd rather not wait 4-6 weeks to get that done. So, I used the grinding compound and worked the valves into the guides. I actually managed to get a very nice fit using the the valve and compound (not too tight or too loose). Did I screw anything up by doing it like that? Also, how loose or tight of a fit should the valves have within the guides? Should they have a bit of wiggle or just move without resistance?

daveleek
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Re: Fitting new valves and guides

Postby daveleek » Mon Oct 19, 2020 11:32 pm

It would have been easier for you to ream your guides and then take the head to an engineering shop to have the seats re-cut thats the method I have used always , I must say the way you used grinding paste is a new one on me , I hope someone comes along with a definitive method for an NH 350
valve and guide job
'

Gui.dorey
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Re: Fitting new valves and guides

Postby Gui.dorey » Tue Oct 20, 2020 7:38 am

I’m afraid that was not a good idea. The abrasive particles of the compound are now imbedded on the surface of your guides and will keep wearing your guides and valves away. You should have used a hand reamer and then lap the valves, or better yet have the seats recut.

Now it’s done, so if you don’t want to replace them, just run with it, but expect to have to replace valve and guides some time in the future. It depends how much mileage you put on her, I suppose.

Always ask first. Lots of experience here in the forum to help you.

As far as the wholes, someone who knows the engine better can probably give you an answer.
Last edited by Gui.dorey on Tue Oct 20, 2020 7:39 am, edited 1 time in total.

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adrie.degraaff
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Re: Fitting new valves and guides

Postby adrie.degraaff » Tue Oct 20, 2020 10:41 am

Gui.dorey wrote:As far as the wholes,

The holes are for the early model with mid guide oil feed but you can use them anyway.

cmattina
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Re: Fitting new valves and guides

Postby cmattina » Tue Oct 20, 2020 2:48 pm

Thanks for the answers all.

Also curious about the running clearance. Right now the valves fall under their own weight, is that enough clearance, or should there be a minute wiggle?

Shipping is my only way of accessing an engineering shop, so is somewhat cost prohibitive for what is already (to me) an expensive project - A very non concourse BITSA project that is costing me almost as much as a numbers matching project (you live and learn).

But it sounds like I may just get excessive wear? For the time it takes to do the valves i don't really mind doing them every few years.

Curious why embedding lapping compound is not an issue on the valve seats for excessive wear? I guess because it is not sliding back and forth?

Gui.dorey
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Re: Fitting new valves and guides

Postby Gui.dorey » Tue Oct 20, 2020 5:08 pm

The seats are hardened, the guides are a much softer metal - cast iron or bronze. So the abrasive will not imbed in the seats.

There should be a clearance spec for your model. Do you have a manual?

Gui.dorey
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Re: Fitting new valves and guides

Postby Gui.dorey » Tue Oct 20, 2020 5:23 pm

Here are the specs for all singles. Measure your parts to see if your valve to guide clearance is ok. If still under, buy a hand reamer and ream the guides to proper bore.
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cmattina
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Re: Fitting new valves and guides

Postby cmattina » Tue Oct 20, 2020 6:13 pm

Gui.dorey wrote:Here are the specs for all singles. Measure your parts to see if your valve to guide clearance is ok. If still under, buy a hand reamer and ream the guides to proper bore.


Thanks,

I 100% appreciate your help and looking that up for me.

I have a vernier that I can easily measure the stem diameter, but the bore hole is another story. I might do the wobble method using a dial indicator?

Is it REALLY necessary to have an exact measurement on these? I kind on want to get it together and running, and then get it perfect. Of course i do not want a valve to seize on my first start up.

Gui.dorey
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Re: Fitting new valves and guides

Postby Gui.dorey » Tue Oct 20, 2020 6:47 pm

The specs are there for a reason - too tight and they’ll seize, too loose and you’ll get oil flowing into your combustion chamber. And other problems which are just not worth it if you are rebuilding the engine.

The best advice is to take it to a shop. If you can’t or don’t want to, then if you have to invest in the proper tools. To wobble the stems or similar is not a method.

At a pinch, at least try to find a rod or shaft that has an outer diameter within the range of the guide bore and which you can measure with your caliper. Use this as a go no go tool for the guide bore. Not ideal, but it is your bike.

cmattina
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Re: Fitting new valves and guides

Postby cmattina » Tue Oct 20, 2020 7:57 pm

It's just tough to find any shops. Closest one is about the distance of London to Edinburgh. but i could mail it.


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