Oversize Valve Guide Dilemma

[SEd27]

I removed my valve guides yesterday to measure for replacement, but ran into a bit of a dilemma…

When I measured the old cast iron guides, I was getting between 0.511”- 0.514”. Granted this is with a digital caliper (I need to pick up a 0-1” micrometer).

However, the project came with x2 new standard bronze guides. I tried for fitment in the bores and it is not even close. If you turn the head upside down the guides will fall out.

Because these dimensions fall outside the available oversize, I am thinking the following are my only options:

1) See if Kibblewhite can produce a custom sizes. I am using their black diamond valves and have already sent them an inquiry.

2) Purchase 850 guides and find a machinist to cut them down to size. I have a lathe but don’t trust my precision.

Has anyone had any experience with this before?

What is the guide size limit 750 head?

I would have not gone down this path but there was noticeable play with the valves inserted. As well, one of the guides had a crack.

 

[concours]

How did you remove the guides? Cold? Hot?

 

[SEd27]

How did you remove the guides? Cold? Hot?

Heated the head in my powder coating oven then tapped them out with a valve guide drift.

 

[concours]

Any thoughts why the holes are bagged out?

Previously pushed out cold?

 

[SEd27]

Any thoughts why the holes are bagged out?

Previously pushed out cold?

Not sure. There were at least x4 previous owners that I am aware of dating back to the earlier 1980s.

There is evidence that some one has been inside the engine and gear box as I have found Japanese bearings.

The head does show some signs of a ham fisted previous owner as there were repaired fins and what appear to be punch/ cold chisel marks.

 

[acadian]

MAP sells +.015 guides

Norton Commando 750 Valve Guides - Intake

Exclusive NASCAR '45'TM Material A Proprietary Alloy as Designed for and used exclusively for NASCAR team is now available for your beloved British bike. Under exclusive arrangement with the manufacturer, MAP Cycle is proud to offer this ma

www.mapcycle.com

But first you need to accurately measure the guide bores. Since you punched them out they are probably scored. If you don't have the proper equipment to measure the bores then you should take it to a competent machinist. Proper guide fit should be .001-.0015.

 

[mdt-son]

Any thoughts why the holes are bagged out? Previously pushed out cold?

Whatever the reson is, SEd27 has to deal with the problem. Speculating why the holes are larger than factory spec doesn't help one bit.

If there are no scores in the holes, they should be measured for ovality. If diameters are equal and pretty even, reaming them will suffice. Then have a machinist turn down an oversize valve guide.
In case you need to provide new bores for guides, there isn't much you can do except try out, as I don'r think a bore limit is known. These are sand-cast heads, and wall thickness may vary somewhat from one head to another.
If drilling an oversize guide bore causes consumation of available wall thickness, I guess you need to scrap the head.
However, if wall thickness isn't a problem, another option is fitting a valve guide liner. With these in place, even a standard valve guide can be fitted.

- Knut

 

[baz]

Check for cracks around the guide boss area

 

[SEd27]

MAP sells +.015 guides

Norton Commando 750 Valve Guides - Intake

Exclusive NASCAR '45'TM Material A Proprietary Alloy as Designed for and used exclusively for NASCAR team is now available for your beloved British bike. Under exclusive arrangement with the manufacturer, MAP Cycle is proud to offer this ma

www.mapcycle.com

But first you need to accurately measure the guide bores. Since you punched them out they are probably scored. If you don't have the proper equipment to measure the bores then you should take it to a competent machinist. Proper guide fit should be .001-.0015.

I have some telescoping gauges, but only my digital caliper. I will have to get the head over to my buddy’s dad place, as he has the proper means for mot accurate measurements.

 

[acadian]

The telescoping gauges are tricky, most don't use the correct technique, you have to tension the pins with the tool at angle, then sweep over the centerline to get the correct measurement, I find ball gauges a bit easier to work with. Set the gauge in your mic, increasing by .0001 increments until the gauge won't fit in the hole, the previous setting will be your actual ID. This all assumes the hole is parallel and concentric of course.

 

[mean gene]

Please find a competent machinist in your area. I understand the process, but. I do a lot of machining and will not do valve guide work. The interference fit is VERY particular to the material the guide is manufactured from. Shops that do this work have a lot of little tricks that they do not share. IMHO

 

[concours]

Whatever the reson is, SEd27 has to deal with the problem. Speculating why the holes are larger than factory spec doesn't help one bit.

If there are no scores in the holes, they should be measured for ovality. If diameters are equal and pretty even, reaming them will suffice. Then have a machinist turn down an oversize valve guide.
In case you need to provide new bores for guides, there isn't much you can do except try out, as I don'r think a bore limit is known. These are sand-cast heads, and wall thickness may vary somewhat from one head to another.
If drilling an oversize guide bore causes consumation of available wall thickness, I guess you need to scrap the head.
However, if wall thickness isn't a problem, another option is fitting a valve guide liner. With these in place, even a standard valve guide can be fitted.

- Knut

If you say so.

 

[concours]

Whatever the reson is, SEd27 has to deal with the problem. Speculating why the holes are larger than factory spec doesn't help one bit.

If there are no scores in the holes, they should be measured for ovality. If diameters are equal and pretty even, reaming them will suffice. Then have a machinist turn down an oversize valve guide.
In case you need to provide new bores for guides, there isn't much you can do except try out, as I don'r think a bore limit is known. These are sand-cast heads, and wall thickness may vary somewhat from one head to another.
If drilling an oversize guide bore causes consumation of available wall thickness, I guess you need to scrap the head.
However, if wall thickness isn't a problem, another option is fitting a valve guide liner. With these in place, even a standard valve guide can be fitted.

- Knut

It helps my own personal curiosity.
JMWO

 

[HopperXL]

It's too late now, but one way to avoid these kinds of problems with the valve guide holes in aluminum heads getting flogged out from too many valve guide changes, is to leave the original guides in place and get an auto machine shop to instal K-Liners.
They ream out the valve guide, in line with the existing valve seat, and install a spiral bronze liner that is then swaged into place. Valve seat then needs minimal or no recutting and guides are not smashed in and out with resulting wear on the holes in the head.

 

[bill]

Thats fine on an 850 guide BUT the 750 guide will break.

 

[HopperXL]

Thats fine on an 850 guide BUT the 750 guide will break.

That's interesting. Could be nasty. I haven't tried it on a Norton yet, but it works on BMW Airheads with great success.

 

[Lineslinger]

I've seen oversized, damaged or scored guide bores sleeved to bring them back to or within spec.

Whatever you decide have a good machinist do the work.
Hang with the guy while he does the work. I learned a whole lot about what I should not attempt (and saved my wallet) by watching and asking questions..

 

[dobba99]

You need to measure the bore for the guide in the head first before anything else. Then make sure it is straight and round and as accurately as possible aligned with the valve seat. This work needs a mill, tilting table, and expanding reamers or similar. Then you can decide on what material to make the guides from. In cases like this i machine oversize guides from cast iron (it wears better than the bronze jobbies) and aim for an interference fit of 0.001" Making guides from cast iron is relatively simple, the trick is to mount them on a mandrel (mounted between centers) to get the OD to size and then you know the OD is concentric to the bore. These engines are now 45 years or more old and the oversize guides available in a lot of cases are just not big enough. I recently had to put new guides in an ES2 head (500cc single, 75 yrs old!) that had to have the guide holes opened out 0.070" larger to get to a straight, round hole. That was way larger than any oversize guide available. If you haven't got the skill or equipment, you are looking for a competent cylinder head specialist familiar with these heads

 

[SEd27]

Thanks for all the responses. I have reached out to inquire with a machine shop that does motorcycle work (though mostly Harley stuff).

I will see what they say when they get back to me.

 

[KiwiShane]

Minimizing machine work...and effort

K-line Interrupted Spiral Guide-Liners

A Useful Solution to Reconditioning Valve Guides and Race Preparation K-Line introduced Bronze Guide-Liners to the market over 20 years ago and is the leader in bringing thin wall bronze liner tech…

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