P.A.W. Diesel Engine

Yes, sorry. Thank you again. Actually it is kind of funny as you mentioned to set it in kerosene for a couple of days there and I had just read it and asked about setting it in there over the weekend, but you already answered it for me here. Just to repeat my post there, I had removed the head screw, cylinder screws (3 on top), prop nut, needle and spraybar assemblies, as well as the rear crankcase plug. I just want to clean it up nicely before dirtying it up. I also tried to remove the cylinder head assembly with no success. I did so by just removing the screws and a gentle twist and pull without any tools, as I know they do ruin things. Thank you.

Just a little update.  I will just soak it in kerosene and not try to remove the head as i was doing some reading and the consensus is to leave it alone.  I would just like to know how to tell if the head is working properly or not. The head screw goes in nice and easy than just 'bottoms out' with a fair bit of threads left.

Although kerosene is the main fuel component for these engines, there will be little benefit soaking it in kerosene as caster oil is not soluble in kerosene alone. The only way that the oil & kerosene are able to mix in the fuel is by the presence of ether. So, dried on caster won't shift with kerosene alone. You'd be better to soak it in glow fuel, or use the same cleaning technique as you would use for a glow engine.
Don't be tempted to screw the compression screw down further than the point where it currently contacts the contra-piston. The contra-piston is a very tight fit in the cylinder and it's common for them to lock solid. If the engine turns over TDC relatively easily, then I would attempt to start it with the compression set where it is. Just snug the screw up against the contra-piston. Don't flood it! If it will fire with a prime at the current setting, you should be able to start it. Once it's warm, back the screw out about a turn, prime and flick, if it fires and you hear a loud "clack", the contra-piston has moved back against the screw & you will now feel lower compression. If that's the case, the contra-piston is loosened in the cylinder and shouldn't pose any problems.
If the compression is too low to fire a prime from the beginning, then gently try to screw the compression screw down about a quarter turn after it firms up against the contra-piston. If it's real tight, don't force it. You need more heat.

Sorry for my long-winded explanation.

Rod.

Rod is correct with regard to kerosene and the compression screw.

From the photograph, the engine looks to be in good condition and little used.

I have a quite a few PAW engines and they are excellent little power houses and very long lasting.

The stiffness will be through gummed up castor oil. I get many in this condition and simply introduce a fine penetrating oil like 3 in One and warm the engine up. I uses a heat gun, wear gloves (sometimes!) and gradually the motor will rock free.

As Rod says, do not work the compression screw - the engine is likely to have been left in an "as run setting" - make sure that the screw is kept slack and DO NOT use it to force movement in the contra piston. Once the engine fires and starts to heat up the contra piston will become movable. Ideally you want it to slacken first.

My advice is not to dismantle the engine unless you think that there is swarf or dirt inside but even then I would err more on flushing out the orifices with WD40.

The back plate on the PAW can be difficult to remove - I use heat and a special tool to remove it. It is also a quite soft aluminium and easily damaged. Most of the PAWs I receive have quite chewed up back plates and I have to reengineer them.

Only strip one as a last resort - they are quite capable of completing self degumming once fired up and running with fresh diesel fuel.

It is difficult to tell the 049 from the 06. They share the same crankcase - the bearer holes on each lug are 11.4 mm apart and 24.6 mm across the bearers. The between bearer fit is 19mm. Standard hole size is 2.3mm but these are often enlarged. The weight of both engines is the same - 75 grams.

These is another do as I say and not as I do. I strip them, remove all marks from crankcase and cylinder head. Polish all machined aluminium (heads, back plates and prop drivers), sandblast/etch the crankcases, spit and polish all components - clean and lubricate them before assembly. I reassemble the piston, gudgeon pin and con rod exactly as disassembled. I have the tooling for all this and have done a few hundred.

Nevertheless, this is more akin to shelf queen creation. If you want to create a runner just use penetrating oil to loosen it up. Once it is flickable - fuel it and fire it. You would be surprised how even an engine gummed on the outside will clean easily when it has been fired up, run and wiped over with hot spent diesel fuel.

I used to be surprised by how many engines I get that are gummed up when a clean and an oil after running would keep them ready to run. However, I have found that it is usually due to them being stored after pranging a model or someone moving onwards and upwards with a different engine while intending to reuse the motor but never getting round to it.

It only takes about a year of no use for the gum up to need work!

Ian and Rod know what they are talking about.

Phil

I was trying to work out which engines size it might be, and it seems a little tricky...

All my PAW engines below .09 have a screw on aluminium head, while the .09 and up have three screws that hold the cylinder. So my guess is that it is actually a .09 engine, but the size of the compression screw indicates a .061...

Surfer_kris wrote:I was trying to work out which engines size it might be, and it seems a little tricky...

All my PAW engines below .09 have a screw on aluminium head, while the .09 and up have three screws that hold the cylinder. So my guess is that it is actually a .09 engine...

Well spotted, I am working on 3 09s at the moment and didn't look closely at the pictures.

The 09 has 2.8mm holes with 15.9mm between them, 29.2mm across bearers and 22.2mm between bearers. Weight 130g or 140g for twin bearing model.

The 15 and 19 are more difficult as they share the same crankcase with 23.4mm between them, 33mm across bearers and 25.8mm between bearers. Weights are the same - 170g or 185 with twin bearings. Hole size 2.8mm.

The weights have to be taken with a pinch of salt as there have been many crankcase designs - as mentioned before, a lot of used engines will have the mounting holes enlarged. Why?

2.8mm is ideal for 6 BA screws and 2.3 mm for 8 BA screws.  The more common (in the UK) M2, M2.5 and M3 are either too large or too small.

Identifying PAW engines by just looking is not easy - below is an example. These are the three 09s I am cleaning up.

The three heads looking from the top look the same



but they aren't!



The plot thickens ..

The cylinder liners have exactly the same external dimensions - the two on the right are interchangeable and the pistons swappable - but the one on the left has a slightly different bore. That engine also has a different crankshaft producing a different stroke - still an 09 though!

Here are the crankcases - the bottom one hasn't been blasted yet and is different to the top two. It holds the left hand cylinder and matching crankshaft. However, the mounting holes are identical.



Still more fettling to do but this one is almost finished and ready to run.







I am missing prop driver nuts, drive washers and an NVA for the other two. I restore engines in batches and then order parts and/or recover them from scrappies. A bit of a production line really.

The compression screws need either polishing or blacking and I may even make spinners for them.

Most PAW engines just need a clean as mentioned before. If they have been sadly neglected the crankcases have corrosion and pitting that stands out. So I sand blast them and seal them them - I quite like that finish.

The heads, back plates and prop drivers adonise easily but they also polish to a chrome finish. the crankcase alloy doesn't take to adonising but will polish. I have a pal who sandblasts and then uses a heat resistant paint on the crankcase followed by an oven bake. I tried that and made a right mess of it! The paint was also expensive!

I decided to have a quick look at my shelf queen PAW engines and ended up feeling a bit of an idiot.

PAW nomenclature varies - 049 is also 80 (.8cc) and 06 is also 100 (1.0cc) - similarly 09 is also boxed as 149.

Anyway, I pulled out a few and had a close look.

Lo and behold - I have both with bolt on heads as well as screw on heads.

Here are some 049s (80s)



and 06s (100s)



As Kris indicated, I cannot tell the screw on heads apart but the engines with the bolt on heads have the back plate marked.

The 049 has "80" stamped on it



the 06 has "100" stamped on it



Doh!

Don't feel even remotely like an idiot.  That is the best part of a forum like this in my opinion.  Learning from one-another.  Thank you for the pics and as well, them are beautiful engines you have there.

ian1954 wrote:I... ended up feeling a bit of an idiot.

Well I hope the idiot didn't mind.  Can't be too careful these days.

Ooops, guess it is my fault, I only have the screw on type on engines below .09, or perhaps I need to check a few boxes here too....

The early screw on type had a colour "coding" to the size (green being .061), so only the later plain head ones would really need the stamp I guess. But it would have been nice with something stamped on a mounting lug there too, just to be sure...

Oldenginerod wrote:

ian1954 wrote:I... ended up feeling a bit of an idiot.

Well I hope the idiot didn't mind.  Can't be too careful these days.

Even if I said that "I feel like an idiot" - it could be misinterpreted with an answer " Where would you find one?"

I simply spray with a colourless fine oil like 3 in One or Gun Oil.

After the sandblasting, the case is rough and accepts dirty finger prints very easily. My fingers are always dirty and it is annoying to pick up an engine and then see a huge thumbprint on the side.

It also makes them easier to clean after running.

After sandblasting the cases are a very light grey but they darken over time to a battleship grey. The oil accelerates that.

I spray on, wipe off and leave overnight before handling it again. After that fingerprints, smudges and castor oil cleans off with a paper tower and adds "patina"

Oil and an aluminium alloy doesn't sound right but it works!

I uses a small airbrush style blaster and very fine aluminium oxide grit.

ian1954 wrote:I simply spray with a colourless fine oil like 3 in One or Gun Oil.

After the sandblasting, the case is rough and accepts dirty finger prints very easily. My fingers are always dirty and it is annoying to pick up an engine and then see a huge thumbprint on the side.

It also makes them easier to clean after running.

After sandblasting the cases are a very light grey but they darken over time to a battleship grey. The oil accelerates that.

I spray on, wipe off and leave overnight before handling it again. After that fingerprints, smudges and castor oil cleans off with a paper tower and adds "patina"

Oil and an aluminium alloy doesn't sound right but it works!

I uses a small airbrush style blaster and very fine aluminium oxide grit.

Do you gize have a product called "ArmorAll" http://www.armorall.com.au/product-types/protectant/ ? This is the best stuff to use for this purpose. It won't burn or cook onto the metal, yet it causes any dirt etc to cling to it, where it can be wiped or washed off without fuss or effort. I've used it for many years on my motorbikes and it works a-treat.

We do have ArmourAll Protectant - gloss and matt. I have never used it though.

I will give it a try. I have also used Swarfega Duck oil but reserve that for my motorbike when cleaning.