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Machining Castings

Forrest A

Registered
Model engines suffer from wet combustion. There have many prolific model engine builders that have used Colman gas (white gas) and WD-40 mix for many years with great success. Bob Shores has written just how much to use. Go to:

http://www.floridaame.org/

Go to "Tips and links", Bob Shores, Tip #10.

Most people do not understand the prperties of WD-40 and its vast benifits. There are a lot of rumors that keep getting passed around. I build stuff that is very small and have found that WD-40 to be the best thing to keep rust at bay and also provide the right amount of lubrication. I buy the bulk stuff (what is needed to mix with the fuel, do not use the spray!) and mix it with Air tool oil for general lube.
 

Manorfarmdenton

Registered
Thanks everyone. I did some Googling last night and found Coleman fuel on Amazon and also the Aspen fuel. The latter is a lot cheaper at £3-96 a litre or £16-15 for 5 litres. I dont think I'll be running my lawnmower on it at that price but it sounds good for the Red Wing.

Re the Red Wing, I now have the main casting finished, the head finished, the flywheels machined but without keyways or governor mounting, and a built-up crankshaft sitting in a vee-block jig waiting for the Loctite to cure. Taking it out of the jig tomorrow and testing for true running will be stressful! John.
 

OTTO-Sawyer

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Age
57
Last Subscription Date
07/15/2019
How did your new flywheels turn out compared to the first set ?

Any pictures to post of the machining & building progress ?
 

deverett

Registered
...built-up crankshaft sitting in a vee-block jig waiting for the Loctite to cure. Taking it out of the jig tomorrow and testing for true running will be stressful! John.
John
You have probably considered it already, but I would advise pinning the webs to the shafts as a belt and braces measure. There will be quite a shock load on the joints when the engine fires. Some builders advocate taper pins across the webs and through the shaft parts, another way would be to insert parallel pins in the interface between the web and shafts.

Dave
The Emerald isle
 

OTTO-Sawyer

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Age
57
Last Subscription Date
07/15/2019
.... another way would be to insert parallel pins in the interface between the web and shafts.

Dave
The Emerald isle
If I'm reading that right, you're talking of using pins like a round key instead of broaching a square hole for a piece of keystock.

I did something similar to that to fix my winch when the winding drum spun on the knurled drive shaft. No way to re-knurl it larger as it was hardened, and when it spun it reamed out the hole in the drum, so I took a carbide end mill and milled 5 notches in the hardened shaft, pressed the drum back on and used the notches to guide an 1/8th inch drill bit to finish the other half of the hole in the drum, then drove 5 nails in as keys to replace the knurl. It was kind of crude way of getting the job done, but it gave me a good solid drive unit that couldn't slip and I didn't weaken the shaft by cross drilling it.

Eventually I overloaded the winch & blew the gears out the side of the housing, but the drum never slipped, although in retrospect, maybe I should have used softer aluminum wire instead of nails so maybe it would have sheared instead of blowing out the gears. Hard to say... the gears were getting worn and would bind up once in a while even before I 'fixed' the drum, so eventually they would have gone anyway.

Made for an easy way to to 'key' the two haves together though without the expence of buying a set of broach bars or setting up the shaper to cut them.
 

Manorfarmdenton

Registered
Good advice again - thank you both. With hindsight the parallel pin method would have been much less obvious, and a lot stronger. Too late though as I have already Loctited it together. Having read some accounts on here I was intending to cross-drill and pin, but am undecided about taper vs parallel, and what size. Suggestions gratefully received! I'm thinking possibly 1/8" silver steel, Loctited in and filed off flush? Taper pins would give a firmer hold though? Loctited in too?

At least I'm pleased to be able to say that the assembly is absolutely true. I gave the Loctite 24hrs in the jig, including a nice warm-up sitting on top of the Rayburn for an hour last evening, then held my breath while I ran it slowly in the lathe to check for runout!

Otto, the replacement flywheels were definitely meatier than the originals, one of which had a pronounced 'twist' as it rotated. I think they have machined up ok. I had a problem with the head casting as well. The protrusion to make the valve push-rod bracket was completely missing on the one that came with the kit! I thought I was going mad at first - because I'm new to this it takes me a while to convince myself its the casting and not me that is at fault! Engineers Emporium replaced it immediately though, and said it wasnt the only one like that. I think they should consider finding a new foundry!

I'll post one or two photos tomorrow if I can work out how to do it.

Thanks again for the moral support! John.
 

OTTO-Sawyer

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Age
57
Last Subscription Date
07/15/2019
... I had a problem with the head casting as well. The protrusion to make the valve push-rod bracket was completely missing on the one that came with the kit! I thought I was going mad at first - because I'm new to this it takes me a while to convince myself its the casting and not me that is at fault! Engineers Emporium replaced it immediately though, and said it wasnt the only one like that. I think they should consider finding a new foundry!... John.
Whether they look for a new foundry would depend on cost/profit, but at the very least they should check the parts before they ship them to paying customers. It would be a lot less hassle for them to throw out the bad ones or send them back to the foundry for replacements than to have to deal with upset customers shipping parts back & forth and getting a bad reputation for selling them in the first place.

If they're Knowingly selling and shipping bad castings to paying customers they won't be in business long as the word gets out. It's good that they stand behind them and replace them, but they shouldn't let them get out the door in the first place.

Maybe an even better "use" for the bad castings would be to offer them customers as "Practice Parts" to help build machining skills before starting on the good parts. That would help them build a better reputation instead of having people complain to them or about them.
 

deverett

Registered
If I'm reading that right, you're talking of using pins like a round key instead of broaching a square hole for a piece of keystock.
That's exactly what I meant. You put it in a more easily understood way.

Dave
The Emerald Isle

---------- Post added at 07:02 AM ---------- Previous post was at 06:57 AM ----------

John

1/8" pins should be just fine. Taper would be better because you can guarantee a good tight fit. If you do use parallel pins, put a slight countersink at each end of the web and hammer the ends of the pins into the countersink - a la rivetting. The pins can then be filed flush. Use loctite with either method for extra security.

Dave
The Emerald Isle
 

Manorfarmdenton

Registered
<<put a slight countersink at each end of the web and hammer the ends of the pins into the countersink - a la rivetting>>
Thanks Dave - I hadn't thought of that. I'm so proud of my first attempt at a crankshaft it will be very stressful weilding a hammer anywhere near it though! The gentle art of filing is another skill I need to learn - my past metal-finishing experience has mostly been with a 9" angle grinder!

Otto - to be fair to Engineers Emporium they told me to dispose of the faulty head casting as I saw fit, and it has already come in handy!

John.
 

OTTO-Sawyer

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Age
57
Last Subscription Date
07/15/2019
... The gentle art of filing is another skill I need to learn - my past metal-finishing experience has mostly been with a 9" angle grinder!
John.
I like that you called it the "Art of filing".

I was lucky, in that my Grandfather showed me a few filing techniques at a young age that have served me well throughout my life. I've saved a few crankshafts over the years that would have required grinding otherwise, and in the process would have been ground undersized, which isn't a problem with babbitt bearings or if undersized bearings are available, but in many cases if a shaft is ground undersized then any pulleys or gears, like timing gears, that are supposed to be a snug fit no longer are. The trick (or art form) there is to keep the file moving around the shaft at a 15-45 degree angle along with moving accross the stroke of the file so you're not filing flat spots grooves or steps. With very light pressure, not much more than the weight of the file itself gliding over the surface you will feel it hit any high spots from nicks & dings that displace material, and then keep going over them in several different dirrections and patterns until you no longer feel it hit or catch. You don't want to apply any pressure that causes the file to leave marks in the good original areas, just lightly polish them. With enough practice, you can do it without even removing a coat of bluing applied to the shaft other than in the raised areas that you're knocking down to blend in. Almost like scraping babbitt bearings, except you're removing material from the shaft instead of the bearing. If you're filing a large flat surface that can be clamped down, then use both hands on the file to control it better and move at a slight angle (5-15 degrees) sideways instead of straight strokes that concentrate in a single area.

It's easier for me to show someone the techniques than to try to put them into words, but using similar techniques I have deburred damaged gear teeth & splines that have either been dropped or damaged from something running through them that shouldn't have like a broken bolt in the rear axle of a friends car one time that caused the gears to lock up. Started with an angle grinder and finished with a file, and it worked like new when I was done with it.

Sometimes it pays to be Obsesive Compulsive as a lot of people wouldn't take the time to do something like that and do it right. Back in the day, filing used to be considered a "skilled labor" and the Stewart Steam Engine kits included notes in the instruction sheets that if the builder didn't have access to a milling machine the castings could be filed to size. I don't know if the newer ones still have those notes or not, but ones from the late 1960s & earlier did.
 

Manorfarmdenton

Registered
Otto, it sounds as if you are a true artist with your file! Thanks for the advice on technique. I know that years ago the file was relied upon far more. The problem nowadays is that we want a quick fix? I know I have always suffered from a serious lack of patience, but building this Red Wing is working wonders in that respect. They say you can't teach an old dog new tricks, but it has taught me to stop and think before I wind the feedscrew!

I have just turned the piston from cast round, and getting it to 3 thou or so smaller than the bore was about the most fussy bit of machining I have done in the 45 odd years that I have owned a lathe!

I just came on to look for the file size for posting photos, then later I'll show the state of progress.
John.
 

OTTO-Sawyer

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Age
57
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07/15/2019
Not sure what the file size limits are, but if you plan on posting a lot of pictures (over time), the smaller the better as you can quickly run out of allotted space like I did.

If you crop them down even just taking a little off the edges, they'll load quicker and save you room for more later.
 

Manorfarmdenton

Registered
Just roughing out the bore, showing the small unmachined area at the top of the cylinder face. I daren't go any deeper as the cylinder was already 1/16" shorter than the drawing stated.
 

Attachments

Manorfarmdenton

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Forgive the multiple posts, but I haven't sussed how to embed the images in continuing text! This one shows how the casting is seriously skimpy under the bearing cap nearest to the camera. I had to set the caps further back than they should be or that stud would have broken out of the front of the base casting. That means the crank isn't central in the caps, but I don't think it will show when the flywheels are on. I have set the timing gear spindle back appropriately, obviously.
 

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OTTO-Sawyer

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Age
57
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07/15/2019
Just roughing out the bore, showing the small unmachined area at the top of the cylinder face. I daren't go any deeper as the cylinder was already 1/16" shorter than the drawing stated.
I could be wrong, but I'm guessing if you had to move the crankshaft centerline back because of the main castings, then you should be able to take a little more off the cylinder face to compensate and still have the compression ratio close to where it should be.

Shouldn't have to alter any of the dimensions, but at the same time, since you're building a single engine instead of mass producing them where you need interchangeable parts, you can get away with altering them where needed as long as you plan ahead and make them match each other like you did with your cam gear location to match the crankshaft location.

With the crank & timing gears moved back, you will need to make the pushrod longer if you don't move the head back by removing more from the end of the cylinder or the face of the head.

Good luck with it ! Looks like you're making good progress so far considering what you have to work with.
 

Manorfarmdenton

Registered
I didn't make any allowances when machining the spigot on the head that goes 3/8" into the bore, and its too late now as I have made the valve seats, but as Engineers Emporium suggested, I can compensate for the small discrepancy in bore length (Otto, it hadn't occurred to me that moving the crank back was an issue there too!) by fitting an annealed copper head gasket of an appropriate thickness. The compression ratio is only about 5:1 I think, and valve clearance isn't a problem as the piston misses the head by about 1/2" at TDC. Not exactly modern diesel engine tolerances!

I got well on with machining the piston this afternoon. I made the ring grooves by clamping a small HSS slitting saw to a piece of ground flat stock in the toolpost, as I didn't trust my grinding skills to make a suitable grooving bit. It made some nice grooves but was slow to use as I had to back it off and blow the teeth clear with the airline about a million times! Tomorrow its on to the mill with it to try to get the wrist pin hole diametrically through it as opposed to tangentially!
John.
 

OTTO-Sawyer

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Age
57
Last Subscription Date
07/15/2019
Any more updates ?

How'd the wrist pin hole work out for you ?

If it's off center a little, if you put the offset down it will help cut down on piston slap, which should be an issue on a low speed engine anyway, and if you put the offset up it will give you a better rod angle on the power stroke producing more torque, but there again, it wouldn't be noticeable on a slow running small model engine.

Perfectly centered might be nice, but it isn't neccesary. Most modern engine are purposely offset up to .090 (maybe more in some cases) to control piston slap, but the drag racers learned years ago that putting them in backwards made more power.

The inportant thing is to be at 90 degrees to the piston whether it's centered or not.

---------- Post added at 09:16 PM ---------- Previous post was at 09:13 PM ----------

Dang Typo's.... I meant to say "which Shouldn't be an issue" Not "which Should be an issue"
 

Manorfarmdenton

Registered
Very interesting comment about the offset. I didn't know that! As it happened my pin hole came dead right, so I don't have to pretend I was going for more torque! The con rod worked out well too, and there are no tight spots indicating the crank or wrist pin not being true. I have put the two cast rings supplied in the kit in the top and centre grooves but haven't fitted the O ring yet. I asked P M Research which groove it went in and they said the nearest one. I haven't worked out which that is yet! Sort of depends which end of the engine you are standing?

The valves were a bit of a challenge for someone used to bigger stuff, but running the lathe at 2000 rpm (its top speed) and using a cermet tip, I got a super finish on the 9/19 stainless rod I was turning down. I havent made the chamfer on the heads yet as my R.H. tool and 200mm chuck got in each-other's way. I have a L.H. toolholder for the cermet tips coming tomorrow, then I'll be able to do it.

So, so far so good. One lesson I learned though - don't have a container of tiny nuts and bolts sitting on the bench with its lid off, and then quickly pick up a worklamp with magnetic base that has inadvertently been sitting on a big spanner. The spanner will drop off the magnet at shoulder height, land on the edge of the container, and distribute the nuts and bolts all over the swarf-strewn workshop floor! I know this will happen as I have spent over an hour today on hands and knees peering under lathe and mills finding them! Luckily I did find all except one bolt. John.
 
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