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Brass cylinder block correction question

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Sam Longley 127/02/2017 15:57:06
742 forum posts
26 photos

I have a 65*65*65 brass cylinder block almost machined for my PYRTE traction engine complete with Phosphor bronze cylinder liner fitted. So the £'s investment is quite high for this component

Unfortunately I drilled the holes from each end of the actual cylinder to the inlet slots badly. One 4mm diam hole came through the inlet slot & into the exhaust slot

If I filled the slots with soft solder & re machined them so that the wall between the inlet & exhaust was effectively soft solder would the solder melt. Is there a big pressure difference which would blow out a 3mm th disc of solder 4mm diam out of place?

My other alternative is to put the whole block into a chuck & machine out a circular flat bottomed hole about 25mm diam & 12mm deep. I could then pres fit a plug of brass in place & re machine the slots.

Could I soft solder this to seal any joints or is there another jointing medium to use or do i need a jointing medium with 2 surfaces of brass that has been pushed hard together

How would the experts deal with this without throwing £50-00 at it for brass & bronze plus a lot of time wasted?


Sam Longley

Martin Connelly27/02/2017 17:25:43
1213 forum posts
146 photos

Could you mill out the web between the inlet and exhaust ports beyond the ports and put a plate in, tight fit and solder? It can't go anywhere if the solder softens.


IanT27/02/2017 17:29:06
1497 forum posts
142 photos

I'm afraid I'm not an expert Sam but given that no-one else seems to be offering a view - I'll chip in.

First - your idea of just using soft solder doesn't sound a great one to me. I don't know the distance between the two "slots" but if there is enough meat there to do it, one possible solution might be to drill through 'tapping' for the next sized (fine) thread tap you have (first checking that you can actually reach the point you need to with your tap (?). Then tap the whole hole and make a 'plug' consisting of a threaded 'end' but with a 'clearance' body. The idea being that you can fill the unwanted 'hole' with a metal screw but still be able to withdraw the unwanted part by cutting it off. You could also of course, fill the existing hole completely with threaded 'rod' and just re-drill out the unwanted part.

I have done this on a much smaller casting and was also able to 'tin' the threaded bit (I used a hot plate/hot air gun to heat the casting) before I screwed it home. You can then (very carefully) re-machine the casting... You will have to think this through to be sure it's possible in this instance, as it's size is a problem.

Your idea of replacing the whole area is also quite possible and I've done similar work fabricating parts from existing/scrap materials - normally silver soldering them together. I also regularly use scrap steel with pre-existing holes in them that I generally drill out to a convenient tapping size and then 'fill' with screwed rod. This is mainly about the cosmetics of a part but when its machined these bits tend to disappear. For large, shallow holes - I clean up the hole and turn a large 'washer to fit which can be screwed in (using studs which are cut off flush) in place and then machined flat.

None of this is engineering excellence - much more about useful bodges that save money by using available material (or correcting my c*** **s). They often take more time to do than starting (anew) with fresh material but that's a personal decision.

So, I'd be pretty sure your problem is correctable but take your time before you just leap in. Sometimes there's a simpler way to do things that only comes after sleeping on it a while.




PS Can't type fast enough. Martin posted whilst thumping this in. Sounds a good alternative and perhaps better on a larger piece. 


Edited By IanT on 27/02/2017 17:31:33

Paul Kemp27/02/2017 17:30:28
422 forum posts
18 photos

Picture might be helpful. Doubtful if ordinary soft solder will last the course, depends on your working pressure / steam temperature. Higher melting point soft solder might do it (Comsol) but I wouldn't rely on it. What is the thickness of the material between the inlet and exhaust ports? Would it be possible to open out the cylinder end of the hole a little and tap a suitable thread in the part you want to plug and then fit a short screwed plug with high temp loctite? That would be a positive definite solution. Another possibility might be to tap the existing hole all the way through and fit a long brass plug and then re-drill in the correct position? I do know of someone who has used JB Weld in this sort of application to recover a cast iron cylinder block where the cored transfer passage was not positioned correctly and ran into a drain cock bore. It's still working as far as I know but it's not something I would do out of choice.


KWIL27/02/2017 19:07:21
3213 forum posts
63 photos

Why not silver solder? Careful heating, should be OK. I have repaired a port on a gunmetal cylinder block succesfully.

Old School27/02/2017 19:56:47
323 forum posts
26 photos

To late to silver solder once you have had a go with soft solder you cannot get it clean enough to silver solder.

Jim Nic27/02/2017 21:06:01
238 forum posts
148 photos

If the engine is to be run on air rather than steam I would be tempted to try filling the hole in the web with JB Weld epoxy filler, simple and comparitively quick. Should that not work then your flat bottomed hole and a plug would be my next choice, I would use Loctite 638 on the plug which would then not need to be a press fit. Give the Loctite 24 to 48 hours to cure before machining.


vintagengineer27/02/2017 21:11:05
468 forum posts
6 photos

I would tap the hole and fit a threaded plug, but I would coat the thread with solder paint so as to seal the joint.

IanT27/02/2017 21:58:47
1497 forum posts
142 photos

I don't think Sam has used anything just yet Old School - so his options are still open.

Kwil prefers silver solder (as do I normally) but I've not attempted to silver solder a lump quite this large (and solid) before, which would require a lot of heat. I have certainly managed to (partially) melt a brass component by applying too much localised heat, so I am somewhat wary where brass is concerned now. There could be some risk of distortion (to the machined surfaces) when applying red heat but I don't know if this would be a problem in practice. I try to machine/tap/thread my fabrications after soldering where possible. Others may have more experience and be able to offer better advice in this regard.

Vintage makes a good point about using solder paste - I'm sure it would help with respect to any soft soldering in this case. Sorry Sam - lot's of "ifs, buts and maybes" here - but hopefully the suggestions will help you find a way forward.

Be good/useful to know what you decide to do and how it turns out.



David Taylor27/02/2017 23:13:41
128 forum posts
39 photos

Martins solution looks pretty good in this case. You're replacing the whole wall between the two ports. I hope I remember the idea if I ever have the same problem. I very nearly did on my current loco - you can see where the drill went into the port wall but I was lucky enough that it didn't go through.

Sam Longley 128/02/2017 08:02:24
742 forum posts
26 photos

Just replacing the wall does seem a first option before i mill out the whole lot

Unless I get some other advice i think that will be the way forward.

Thanks for the suggestion Martin

The wall is 3mm thick

the inlet slots are 6mm long * 6 deep

the exhaust slot 9mm long * 9mm deep

As IanT suggests silver soldering a large lump of brass is not really on for someone with my limited ability of silver soldering. It will be hard enough getting enough heat to soft solder, so I will have to research some form of locktight

Jim Nic suggests 638 so i will look that up


Edited By Sam Longley 1 on 28/02/2017 08:07:24

JasonB28/02/2017 08:12:10
17824 forum posts
1948 photos
1 articles

648 is better at higher temps than 638 if you are going down the loctite route.

Michael Gilligan28/02/2017 08:39:13
15450 forum posts
668 photos
Posted by JasonB on 28/02/2017 08:12:10:

648 is better at higher temps than 638 if you are going down the loctite route.


It's also worth noting that both products were updated for 2014

This press-release from Henkel gives a useful summary: **LINK**

So [despite my general enthusiasm for using old stock]: For Sam's purpose, the later version offers a substantial performance advantage.


Jim Nic28/02/2017 09:33:53
238 forum posts
148 photos

Oops! Sorry I didn't read the question properly and missed that it was PYRTE we are talking of here. My suggestions are of no use in this case.


Nick_G28/02/2017 13:15:40
1808 forum posts
744 photos


Will this help.?

Don't know if it's 'machineable' like normal JB



Sam Longley 128/02/2017 13:23:52
742 forum posts
26 photos





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