My apologies about the big delay in giving some solutions to detail soldering problems.
My experience building superdetailed, kitbashed and scratchbuilt brass/nickel sliver models led me to a solder/flux combination that revolutionized my soldering experience. That solder/flux combination is 96/4 Tin/Silver coreless solder and Superior Supersafe No. 30 Solder Flux. Both the solder and flux are available here:
https://www.hnflux.com/Frankly, using this combination will turn you into an expert solderer for small parts in N-scale. Also, your construction will last longer and be much more durable because 96/4 Silver/Tin solder is 6 times stronger than Tin/Lead electronics solder. Additionally, your solder joints will be bright, the solder will flow quicker and be thinner.
An important point is Superior Supersafe No. 30 Soldering Flux is self-neutralizing, so it won't eat your model a couple of years after you've painted it.
For the vast majority of my soldering efforts when building PCB turnouts, making handrails, ladders and other small wire parts, I've used my old Realistic 35W soldering iron with a small wedge tip.
I make sure the iron's tip is clean and tinned for EVERY solder joint...with a minimum of tinning on it.
Having a solder stand with a very damp sponge is absolutely essential along with a small can of tinning paste.
For precise placement and making sure that I don't use too much solder when I'm making very small joints, I flatten the end of my solder with my flat-nose pliers, then split the flattened portion with a sharp #11 X-acto blade making two "whiskers" which usually form a small "V" at the end of the unflattened solder wire. This makes a much finer strand of solder that will melt much quicker and apply much less solder to your joint.
For precise solder jobs,(A) I make sure that the brass/bronze/nickel silver pieces are clean and burnished. (B) Burnishing is easily accomplished using 400 grit sandpaper, or flat pieces, such as PCB ties, can have the oxidation burnished off using a simple pencil eraser. (C) For degreasing on parts that I've fabricated by holding them and bending them...I use Bestine Rubber Cement Thinner...which is also known as Heptane, to remove skin oils which inevitably contaminate metal parts if they're handled with bare fingers. Bestine/Heptane evaporates almost immediately and I just use a stiff, small brush to brush it on to what I am going to solder. Always make sure you tightly close the can of Bestine/Heptane as it and its fumes is/are highly flammable.
After I burnish and clean the parts, I use the gel version of Supersafe No. 30 flux because it stays localized and concentrated in the spot you want it to stay. For some applications, I will tin the parts first with the silver bearing solder... then position them where I want, flux them again and apply heat without adding any additional solder. This "tacks" them together, and I will then test the joint to see if I need to add a small amount of additional solder. Depends on the application...sometimes I have to, sometimes I don't.
I rarely have blobs of solder forming on my joints....like NEVER. Blobbing means that your flux is not working or that you're not getting enough heat to your joint...sometimes a combination of both...and maybe your parts are dirty or oxidized. Solder that is properly fluxed and done at a hot enough temp runs ("wets")...it doesn't blob.
After I'm done with soldering my model, I wash it with warm water and a mild detergent.
In your case, I would make sure the tip of my iron is in good shape...that it's at least a 35W iron...clean and tin its tip and desolder the blobs using small diameter desoldering braided wick. Then, resolder the joints using the 96/4 Tin/Silver solder (flattened and split) after having fluxed the joint with your new Superior Supersafe No. 30 Soldering Flux.
All that being said, the second most important thing I did to do precise soldering joints for model work, was to bite the bullet and pay for a 250W American Beauty Resistance Soldering Station, with the "probe" handpiece and the "tweezer" handpiece...and extra tweezer tips and probe tips. I use this almost exclusively now for building turnouts, making brass models of trackside structures and superdetailing imported brass models.
The main thing that the resistance soldering station does is allow you to position, clamp, solder and let cool in one operation using the probe or tweezer to position and hold the part, keep it in perfect position while you step on the foot pedal...and solder...then let off the foot pedal while the part cools...then release the joint after the solder has solidified.
If you are doing a lot of brass superdetailing, and plan to keep doing that kind of work...it is well worth it to purchase a top-notch resistance soldering station, and sometimes they are on sale.
Photo (1) - Superdetailed and modified Hallmark "UP Welded Caboose" turning it into an accurate UP CA-8 with old parts removed and new, finer parts soldered on:
For this model, I bent and soldered the grabs to the brass body without using mounting holes...just using the solder joints and flattened grab wire ends. The silver bearing solder is strong enough to allow this type of solder joint to be reliable and robust, whereas I would not do this using 6 times weaker Tin/Lead solder.
I am looking forward to further photos of your engine project!
Cheerio!
Bob Gilmore
