Ready machined inside cylinder block

[David HaynesParticipant @davidhaynes53962]

I am interested in buying a ready machined inside cylinder block for a loco I am hoping to build. It will be some time before I actually need it but the cost and time saving is potentially great I am not one to buy things 'just in case', but this is a project for which I have been already been producing construction drawings and thus I am already fairly committed. The overall width, between frames, of the cylinder block is correct but the length is 8.4mm short of my requirements. That discrepancy may be just due to the rear cover bosses. The inside depth from the rear of the block to front cylinder cover is right and the bores are correct (or within 1/64&quot.

However, the ports (4mm x 12mm steam and 6mm x 12mm exhaust) are quite a bit different than what I want (2.4mm x 17.5mm steam and 9.5mm x 17.5mm exhaust). My concern is, as the design I am producing is based on a proven cylinder pair, is it worth trying to change the port dimensions on this ready made item. If this is the case, I wonder how successful people have been in blanking and re-boring ports; what is the best filler?

Many thanks, Dave

[David HaynesParticipant @davidhaynes53962]

Feasability for adapting to fit my own needs

[JasonBModerator @jasonb]

As the areas are about the same the easiest method would be to fit a thin CI or Bronze plate over the existing ports with your new holes cut into it. This method is used if cast ports have not come out right or if they have been machined wrongly.

J

[David HaynesParticipant @davidhaynes53962]

Thanks Jason,

I will look at grades of bronze suited to bearings. Does anyone have any thoughts about PTFE as an alternative for this replacement valve surface. I see no drawbacks in this material, bearing and heat properties seem fit for purpose and any slight compressibility is perhaps not a problem in this application.

Thanks

Dave

[JasonBModerator @jasonb]

Biggest problem will be sealing it against the existing valve face as not a lot sticks to PTFE. If its not sealed you will get steam tracking between the inlet & exhaust ports The metal plate can have a smear of slow set Araldite or JB weld and a couple of small CSK brass screws.

Have a look at this and the previous 10 or so photos

[Sub MandrelParticipant @submandrel]

I'm sure ptfe would make a good valve block though.

Neil

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