The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Russ on 06.07. 2014 11:29

Title: Valve guide clearance
Post by: Russ on 06.07. 2014 11:29
Hi guys,
Just checking what the experts on this forum have learnt over the past forty years or so with regards to valve guide clearance.
I have just fitted new iron valve guides in my 51 A10 iron head, to which I will fit the original valves.
The valves are in good condition and are a very neat fit in the new guides, which will be reamed to suit, and the seats will then be cut in.
I have researched the forum on this topic and have the recommended clearances in the Haynes manual, page 14, but would appreciate your input as to what clearance I should give the valve stems in the valve guides.

Thanks Russ
Title: Re: Valve guide clearance
Post by: edboy on 06.07. 2014 15:10
hi russ, personally i would only ream if you felt a tight spot when moving the valve up and down before assembly . i assemble with graphogen as do a lot of other rebuilders to lubricate on initial start up. i ve also read of a mod where the top of the exhaust guides are countersunk slightly to pool a little oil for cast iron guides but no idea if it works.
Title: Re: Valve guide clearance
Post by: muskrat on 06.07. 2014 20:39
G'day Russ.
Try for 1 to 1 1/2 on inlet and 1 1/2 to 2 thou" on ex.
Cheers
Title: Re: Valve guide clearance
Post by: trevinoz on 06.07. 2014 22:09
What Musky said, Russ.
Don't have the exhaust guides too tight or you will be pulling the head off pretty soon after you get it going. Maybe the barrel too if the piston hits a valve.

Trev.
Title: Re: Valve guide clearance
Post by: Russ on 06.07. 2014 22:16
Thanks all,

That's exactly the advise I was after, appreciated.
Russ
Title: Re: Valve guide clearance
Post by: wilko on 07.07. 2014 00:19
How do you measure the valve guide bore?
Title: Re: Valve guide clearance
Post by: bikerboy on 07.07. 2014 01:43
How do you measure the valve guide bore?

Why would you need to? Measure the valve stem and then use a reamer to suit?

What happened to the days of just whacking a drill thru it after hammering it in the head cold?  *smile*
Title: Re: Valve guide clearance
Post by: BSA_54A10 on 07.07. 2014 09:16
lightly oil the valve stem.
Hold the head upside down
Drop the valve in the guide.
If it sits there then your clearences are not small
If it drops slowly then they are about right.
If it drops strait through then they are too big.
Title: Re: Valve guide clearance
Post by: Jules on 09.07. 2014 14:21
what grade oil Trevor and at what temperature... *smile*
Title: Re: Valve guide clearance
Post by: BSA_54A10 on 10.07. 2014 03:31
I usually use light machine oil because it washes off my fingers easily.
If you have a comprehensive drill set then you can use them as a rough bore measure.
]The other way is to stick you finger over the guide hole and pump the valve.
If it sticks to your finger it is about right.
Sort of like the thumb over the plug hole compression test.
Title: Re: Valve guide clearance
Post by: Colsbeeza on 26.08. 2018 13:37
More on Valve Guide Clearances.
I have detailed my cylinder smoking problem earlier in the forum item below:-
          https://www.a7a10.net/forum/index.php?topic=13316.msg107462#msg107462
A quick summary - after running for 40 miles, the GF is smoking severely on the Left Pipe. It was excessive and wasn't settling down, so  I have taken off the Cylinder block and head. The compression test implied glazed bore on the LHS.
I certainly think that I have glazed the bores due to lengthy problems getting it to run enough to ride it.
However, the valve guides were something else.
There was one odd type with a non-tapered top, and all 4 had been "knurled" inside - like there is a thread in each guide presumably to enlarge the ID of the worn guides, not cut but rolled in and then reamed to suit the valve stems. I believe this was sometimes done to lengthen the life of the guides at little cost, but was never intended to last very long. I imagine this would also accelerate wear on the valve stems due to reduced surface area.
Anyway, I measured the clearances - all are at least 8 thou, and the Left exhaust is at 10 thou. *problem* I would say R**ted.!
That probably explains a lot of the smoke. I measured the valve stems, and they are all worn a little - the clearances compared to a new uninstalled guide (5/16" = 0.3125") are all from 2.5 to 3.5 thou. That suggests valve stem wear of 1 to 2 thou. Stem ovality is good I think, the worst being about 0.6 of 1 thou.
I will replace the guides with new Cast Iron Guides, but am wondering whether the new guides when compressed to fit will be a little reduced in Inside Diameter - just a thou or two would do. I hope I don't have to buy new valves. I'd like to know whether I should go look for new valves now or wait until I can measure the installed guides which may be a few weeks.
Does anyone have experience whether the guides ID will shrink a few thou when installed.??
Cheers Colin
Title: Re: Valve guide clearance
Post by: coater87 on 26.08. 2018 14:41
CB,

 I installed cast Iron guides and new valves when I rebuilt motor.

 The guides I bought (cast Iron) did not fit on the stem when they were out of the bike and it did not get any better once popped in.

 I used a 5/16 hand reamer then sent the head in for centralizing.

 I kind of now wish I would have had the shop do the reaming also. The smoke from the left side has all but disappeared after the re-torque of the head, but I bet those reamed guides are all on the big side.

 Maybe I will look around for a spare cast iron head, and have the entire thing done properly on a sunnen valve machine by people who know whats what this winter.

 I also believe that valve seals from a Harley sportster could be made to fit our bikes, I will have that done if they are able.

 As far as getting 3 thousandths out of the shrink fit? The oversize metal has to go somewhere, but I dont know if you will get all of three out of it. A guess on mine about 1 to 1.5 shrink. You might be OK using a -.001 or even -.002 reamer for the quides *????*

Lee
Title: Re: Valve guide clearance
Post by: Triton Thrasher on 26.08. 2018 15:04
i ve also read of a mod where the top of the exhaust guides are countersunk slightly to pool a little oil for cast iron guides but no idea if it works.

There’s another mod where the top of the guide is bevelled to make oil run away from the valve stem.
Title: Re: Valve guide clearance
Post by: chaterlea25 on 26.08. 2018 23:19
Hi,
Ream the iron guides  to 0.3125 (5/16)
The valves should be sized to give the correct clearance to this
Different story with ally head and fancy
guide material

John
Title: Re: Valve guide clearance
Post by: Colsbeeza on 27.08. 2018 00:06
Thanks Fellas,
As an afterthought - Because only the central portion of the guide is shrunk in, is it likely that only the centre bit shrinks, leaving the guide tapered outwards at both ends.??
In which case, I cannot win with the old valves.
John CL, are you saying that you get the valve stems ground to fit the guide bores.? I have not heard that before. My unfitted new guides are already at 0.3100".
Any experience with the new Hepolite valves.?
Colin
Title: Re: Valve guide clearance
Post by: edboy on 27.08. 2018 10:55
this thread started 4 years ago.
is it a record?
Title: Re: Valve guide clearance
Post by: duTch on 27.08. 2018 11:01
 
Quote
this thread started 4 years ago.
is it a record?

 No, I think bergs re-set that when he questioned the bigbangbirth of the forum a few days ago
Title: Re: Valve guide clearance
Post by: edboy on 27.08. 2018 11:09
i think it was the introduction of motorways which created the bsa big bang event