From what material are valve guides made and are there o/s ones.

John

email (option): john.kater@chello.nl

They are cast iron in an M20. I'm not aware of any oversize guides off the shelve. It would be quite simple for a precision engineer to make some oversize guides. I don't know if there would be any advantage in Bronze guides in our old SV's.

But what has happened to your barrel that you need them oversize? Ron

email (option): ronpier@talk21.com

Ron, I bought a barrel because the old one has broken and sharp fins. But the top of the valve guide was damaged or "crumbled" therefor I want to replace it.
The guy in the workshop wants to drill it out instead of pressing it out. He told me that he would need an o/s guide. Making sure the valve has good contact in the valveseat. I hope it makes any sence. Al least this is what I understand.

John

email (option): john.kater@chello.nl

The guide should be drifted out from the bottom upwards using a suitable drift and hammer..NOT drilled...

The replacement guide can be fitted using the same method...

Note the stepped drift should have a sharp corner between the 'pilot' diameter that fits into the guide and the larger diameter that drives against the guide when struck...

The exhaust guide is couterbored and it should be fitted with the counterbore at the upper end...

Note also the distance measured from the top (head gasket) face of the barrel to the end of the guide after fitment...That is shown in the workshop manual and the guide should be drifted in sufficiently to conform to that..

The guide bore should be sized after fitting to give a .0035" clearance to the valve stem and the exhaust valve seat should be LIGHTLY recut to true it to the valve and then lapped...

Whilst a change to bronze is possible I wouldn't recommend changing the valve guide material unless you are ready to experiment with materials and clearances...Cast iron guides should be made from grey cast iron in G1 or G2 grade...There are no oversize guides available..

Note that the condition of the existing valve guide is completely normal in an M20/21 engine that has completed a high mileage and unless the guide is actually loose in the barrel an oversize guide won't be required...

I've never seen a loose guide yet in the numerous M20 engines I've rebuilt in the last 40 years...Ian

email (option): ian@wright52.plus.com

I would suggest you don't use that workshop again. If what you said they said is true they don't know what their doing.

Thanks Ian,

Tomorrow morning I go to the workshop and take the barrel back depending their answer.

John

email (option): john.kater@chello.nl

Just take it back full stop. The guy's clueless and no answer changes that.

"He told me that he would need an o/s guide. Making sure the valve has good contact in the valveseat. I hope it makes any sence."

Nope, in fact makes very little sense. Agree with what was said by others, take the barrel back. They guy i clueless.
This may sound a bit harsh, but if thats what the guy said it is apparent that he has never looked at an M20 manual, or maybe even worked on a sidevalve or other engine of this period.

There are people on this forum you could ship to if you don't find someone locally.

best regards,

Simon

Thanks for the info. Last week I took the barrel back. He told me always drilling the cast iron guides out, (by the way a very costly operation), because drifting them out would damaged the barrel and guide and make things worse.
I ordered the special tool and do it myself.
But first I will try it with the old barrel.

Anyway why not pressing them out ?

John

email (option): john.kater@chello.nl

You can press them out if you have access to a suitable press...I like using a fly press personally as it has more 'feel' than the hydraulic alternative but there are few fly presses around these days large enough for this job...

However, either will do if appropriate care is taken to ensure it's set up correctly...

You can use the drift you are buying as the pressing tool...

Note my original post regarding how far to press in the replacement guide...They do not have a 'shoulder' to press up to..Ian

email (option): ian@wright52.plus.com

Good for you John!

Can't really see why drilling out would be pricier than drifting/pressing. Unless there's a cost for using the machine of course. Which would make some sense I guess.
Anyway you're better of this way.

It actually never ceases to amaze my what "professionals" will recommend (and charge you for). Throw in a bit of male self security and lack of listening and you're set to go to run a business I guess.

It should be duly noted that I am certainly not a fully skilled mechanic, but even I can time and time again call out "professionals" on their lack of workmanship. Kinda makes you wonder...

But then there is the other side, all the extremely skilled people who know everything there is to know, and the some.

(I also am very fond of the fly press by the way, but bearings I find I like to press with hydraulic for some reason)

This is typical of a mechanic who is use to working on modern motorcycles where guides are designed not to be repaceable and are in alloy heads.

When all is said & done, how M20's would come into his shop in 12 months ?
The days of walking in with a barrel and the mechanic saying "Arh an M20 barrel. haven't had one of them in here for a while, lucky there are some ols chill cast guides in the parts room "

I had my barrels resleeved 20 years ago.
Walked in & the boss looked at it & said we can bore it out but +60's are real expensive but we can do you a new liner tomorrow"

Now I did not put the gudgeon clip in properly and thus it needed a rebore 6 years latter.
Armed with the new piston I had to take it back 3 times before the new shop would boree it out with enough clearence and only then after I signed the work order and a disclaimer.

email (option): bsansw1@tpg.com.au

['Armed with the new piston I had to take it back 3 times before the new shop would boree it out with enough clearence and only then after I signed the work order and a disclaimer']...

A point well worth noting...Always take the time to establish the correct clearances before approaching a modern engine shop that isn't familiar with old engines...

Faced with a lack of the relevant information they will apply a modern 'rule of thumb' measurement that will nearly always be too close..

The chap who runs my local shop still struggles in his head with applying the clearances I supply him...Being used to modern tolerances he thinks either the engine will be worn out from the outset or it won't work correctly.
He can't believe the 4.9-1 compression ratio either... ..Ian

email (option): ian@wright52.plus.com

A few hours ago I recieved the tool and 10 min. later the valve guide was removed from the barrel. Price: eng pound 18,75 labour: nothing. At 69 I work for free.
The new guide is in the freezer I hope it helps for an easy fit.

Thanks again .

John

email (option): john.kater@chello.nl