Honda 50cc valve-guide reaming?

[ffoy]

Hi folks.

I thought I was being clever and bought NOS inlet and exhaust guides for my little Honda head (SS50).

Problem is they are supplied undersize (the bore) and need to be reamed to correct size to enable the valves to fit inside.

I don't know who to approach to get this done. I live in Glasgow and there isn't a wealth of enthusiastic restoration-minded businesses around so would prob need to take it a a car-engine re-conditioner. Past experience tells me I'll either get ignored at the counter or sent on a wild goose-chase round neighbouring shops and end up being referred back to the one I started at.

Sorry if I've offended any patriotic Scots out there but that's been my experience locally. Anything from trying to buy paint at motor-factors to getting bolt removed by spark-erosion. Disaster 

[Tomb]

I ream out my own, or lap the holes using silver steel polished down and lapping paste (grinding paste) the problem with this in cast iron guides like yours is the paste can be a pig to get out of the metal.

The other problem with reaming is concentricity/squareness, you need to use an old reamer with polished down lead to guide in the reamer, then when more material needs to be removed, raise the cutting edges with a HSS lathe tool drawn across the cutting edges. Its old school stuff but easy and cheap. Its good doing your own because you can "fit" them to the valves you have.

Also ream AFTER fitting as the different "fit" of the guide in your head may close the guide if tight. If the head is worn the guide can be Knurled before fitting.

If you own a lathe you can make your own guides, I make mine from Ali or Phozy Bronze.

And strictly speaking you should have the seats recut, but if you're accurate with the reaming you can get away with a valve regrind.

[ffoy]

Thanks Tomb  . That's the sort of reply I like. ie it's do-able if you observe rules x, y and z.

[Bryanj]

DO NOT use a car shop they won't do it accurate enough, try a big Honda dealer they should have the correct Honda reamer which is an odd size

[ffoy]

Thanks Bryanj. Afaik the nominal size of the valves/guides is 5.5mm. So they'd need to be reamed to within some recognised tolerance of that.

[Tomb]

A 7/32" reamer will give 5.56mm, an old one will give 5.5mm but measure your valves, you may find they are smaller than the nominal size.

A couple of years ago I was asked to look at a GSXR with oil burning problems, new guides and seals had been fitted but the brand new valves had stems that measured below the wear tolerance in the factory manual. ALL of them! So reaming to the stems of your valves is a good idea.

[AshimotoK0]

Thanks Tomb  . That's the sort of reply I like. ie it's do-able if you observe rules x, y and z.

I must say Tomb ... I am really appreciating reading your replies to other member on here. Straight talking replies giving advice from what, I am certain , is a wealth of mechanical knowledge that you have on our  bikes. You were absent for quite a while on here but I for one really appreciate your input .. to me that's what these forums are all about.

BTW I have found a couple of CB72/77 RH  alloy crankcase  covers that need repair, so I will be in touch.

[Tomb]

Thanks Ash, kind words. As you and a few others know I was absent from here for similar reasons to yours, I was conned/ripped off by a regular member on here, he hasn't been here for a fair while hence my return. It was a tiny amount £ but the trust broken from someone on here bites deep.

Moving on.....

I have some experience of Honda SOHC's but nothing compared to the regular lads here. What I do have from 18 years Toolmaking and a further 18 years Mech Fitting is lots of old school engineering experience that is probably more relevant to old British bikes, now our bikes are getting older I'm finding its getting useful on old Jap iron. If I can pass it on to help others I will gladly as a way of repaying the valuable advice I have had (and will need in the future on my 500 rebuild)

CB77 cases? Thanks, I'm sorry I have not looked for the fork parts you need just yet, personal stuff getting in the way, I'll PM you.

[MCTID]

Try 'Tracy Tools' - www.tracytools.com in Torquay for Reamers.

I have bought a few Drills and Taps from them and they are really helpful. I made a booboo on my latest purchase but a Guy phoned me to check before he despatched my order........that's what I call 'Excellent Customer Service'.

[Tomb]

Tracy don't appear to sell a 5.5mm but ring and ask as they may not list less common sizes.

They are readily available though
http://www.ebay.co.uk/sch/i.html?_from=R40&_sacat=0&_nkw=5.5mm+hand+reamer&_sop=15

Hand reamers appear to be more expensive than machine reamers, machine reamers can be used with care, but be wary of getting out of square, this will cause valve seat lining up issues that you really don't want.

[ffoy]

Great advice and input. Thanks guys. I've also bought from Tracy Tools before and do like the company.

Anyway I've measured my NOS valve stems (with vernier caliper) and they are 5.4mm, maybe a shade under - 5.38mm.

Looking online the most common figure(s) I'm seeing for clearance between valve-stem and guide is 0.02mm - 0.05mm so looks like I'd be aiming to ream mine out to 5.42mm perhaps....