Starting with the Boll Aero 18

Help Support HMEM:

mr-mechanical

Member
Joined
Apr 30, 2020
Messages
15
Reaction score
9
Location
Cumbria, UK
So tomorrow I plan to make a start on my first model engine.

I have choosen the Boll Aero 18. I have the drawings and 90% of the materials. Tomorrow I plan to machine the crank case.

I will make sure I take plenty of photo to share here.

Do you have any tips?

Also, looking at the drawings for the crankshaft itself, the drawing says to loctite the crankpin. What type of loctite is best for this application?
 
Last edited:

mr-mechanical

Member
Joined
Apr 30, 2020
Messages
15
Reaction score
9
Location
Cumbria, UK
So today I made a start on my first model engine and made the crank case for the BollAero 18.

This part was my second attempt as with the first part I was immediately unhappy with the position of the first hole drilled / bored..

But started again and I'm happy with this part.

I've had a look around and I plan to use loctite 638 for the crank pin.

Now to decide which part to make next.

IMG_20200516_115423.jpg
IMG_20200516_115428.jpg
IMG_20200516_144218.jpg
MVIMG_20200516_151552.jpg
 

mr-mechanical

Member
Joined
Apr 30, 2020
Messages
15
Reaction score
9
Location
Cumbria, UK
Last week I started on the crank case cap. However after a few minutes of frustration with my lathe I decided to take the cross slide apart and open up the diameter of and replace the gib screws.

The hex in the original ones were rounded and which ment I couldn't adjust them anymore.
However while drilling them out I found that I wasn't able to drill through once hitting half way point. Not sure if the material hardened or what. Eventually I managed to get a 2.5mm carbide drill through (the only carbide drill I had), but a 5mm HSS drill for the new M6 threads still wouldn't go through.

Anyways.... Today I received a 5mm carbide drill which went through no problem. Got the lathe back together and parting operations are massively more successful!

Sorry for rambling on about my lathe, here's what your here for... Today's progress on the Boll Aero
IMG_20200526_161124.jpg

Hopefully tomorrow I'll make some more progress on the engine... Assuming I don't decide to dismantle / fix something else.
 

ixb1

Well-Known Member
Joined
Feb 16, 2015
Messages
52
Reaction score
29
Location
CZ
My first engine was Boll aero too.
If you want made crankshaft with separate crankpin, i dont recommend use loctite.Crankpin must be pressed into web.Slide fit+ loctite leads to fail.Imo best option is one piece crankshaft.
It be better make cylinder with bigger bore diameter- bigger displacement is better :)
 

mr-mechanical

Member
Joined
Apr 30, 2020
Messages
15
Reaction score
9
Location
Cumbria, UK
Thanks for the tips. I'll have a look into turning the crank as one part.

How do you approach turning a crank? At the moment I think I would do it between two centres
 

ixb1

Well-Known Member
Joined
Feb 16, 2015
Messages
52
Reaction score
29
Location
CZ
Its more ways to turn crankshaft. I personally turn them in four jaw chuck out of ht bolt.
Plans do not contain one important note- cylinder bore must be tapered!
 
Last edited:

KenC

Active Member
Joined
May 30, 2016
Messages
42
Reaction score
13
Location
S W France
Its more ways to turn crankshaft. I personally turn them in four jaw chuck out of ht bolt.
Plans do not contain one important note- cylinder bore must be tapered!
The Boll engine is for beginners and the main idea is that it should simply run, it is not meant to be a power house. It does not need a tapered cylinder bore at all, that is for engines with a decent amount of performance and the ability to hot re-start easily. A perfectly parallel bore which is perfectly round and with a highly polished surface finish is the thing to aim for. If the builder really wants to taper the bore, the exhaust port area should be perhaps one thou smaller diameter than the bottom of the cylinder, and at top dead centre the cylinder bore would be one or two tenths of a thou smaller than the exhaust area. I would respectfully suggest that a beginner to model diesel engines will be hard pushed to produce a round and parallel bore rather than barrel shaped, and may equally be hard pushed to measure the bore taper accurately without the use of a bore comparator.
So forget tapered, round and parallel with a fine finish will do for now.
Ken
 

Mechanicboy

Well-Known Member
Joined
Jul 10, 2013
Messages
707
Reaction score
230
The Boll engine is for beginners and the main idea is that it should simply run, it is not meant to be a power house. It does not need a tapered cylinder bore at all, that is for engines with a decent amount of performance and the ability to hot re-start easily. A perfectly parallel bore which is perfectly round and with a highly polished surface finish is the thing to aim for. If the builder really wants to taper the bore, the exhaust port area should be perhaps one thou smaller diameter than the bottom of the cylinder, and at top dead centre the cylinder bore would be one or two tenths of a thou smaller than the exhaust area. I would respectfully suggest that a beginner to model diesel engines will be hard pushed to produce a round and parallel bore rather than barrel shaped, and may equally be hard pushed to measure the bore taper accurately without the use of a bore comparator.
So forget tapered, round and parallel with a fine finish will do for now.
Ken

With parallel cylinder, you will lost compression due heat of expansion then the engine can't run after the engine is started up. It's not difficult to create parallel shaped cylinder.

Do it as i wrote here:

Lets take a look at a typical lapping job - that of producing a fine finished bore and piston for an IC engine. In fact, piston and bore are both lapped in separate operations (NOT both together). All of these operations will be carried out in the lathe (and I need hardly mention the importance of keeping lapping compounds off the machine, particularly the chuck and slideways). For the bore an expanding lap is ideal, and this should be some 3-4 times the total length of the bore. The first grade of abrasive would be mixed with light machine oil (10W or lighter) and liberally coated on the inside of the workpiece. Similarly, the slurry would be added to the outside (and inside assuming it is of the ventilated type) of the lap. The lathe would be started at about 300rpm (for a nominal 1" bore) and the lap passed rapidly through the bore, keeping it moving back and forth without it coming out the bore. How to hold the lap? well, perhaps the best way is with a 'floating' tailstock holder, and failing this holding with the hand is a method as good as any. Be careful when holding the lap by hand as it's possible it may jam, hold it lightly and expect the unexpected. Remember also that unless the lap is maintained dead parallel with the bore (an almost impossible task) it will tend to bell-mouth the bore a little - hence the reason for making the work a little longer than finished size and trimming to length later. When the inside of the bore has achieved an all-over grey appearance, with the fine scratches appearing even and criss-crossing both ways, and with no evidence of any deeper scratches (as might be left by the reamer) it's time to move onto the next finer grade. The work will have to be removed from the chuck to clean it properly, and this should be done with clean paraffin oil followed by hot soapy water. The same procedure applies to the lap and all traces of the abrasive must be removed. The process continues until you reach the 'flour' grade of abrasive by which time the finish on the workpiece should be very fine indeed. A final polished finish, should this be deemed necessary, can be achieved using metal polish (diluted Autosol, or some liquid chrome cleaner). The lap should be a separate 'finishing' lap so there is no chance of contamination with the coarser grades of abrasive which might be embedded in the main lap. The piston is treated in a similar way except of course the lap is female. Work will continue with the coarse abrasive until (using the un-trimmed bore as a gauge) the piston will not *quite* enter the bore. At this stage finer grade abrasives are used and work continues until the piston will just enter the bore tightly. At this stage, it is usual to finish mating the two parts by using metal polish and briefly using the piston to lap the bore directly. Great care needs be taken but this method ensures that the fit is good for the entire length of the bore.

The piston/sleeve are ready to use when the piston goes tight in sleeve while the parts are dry and without oil and piston goes easy in sleeve until tight in top of dead centre in sleeve with oil applied.
 
Last edited:

KenC

Active Member
Joined
May 30, 2016
Messages
42
Reaction score
13
Location
S W France
On the other hand you could read my guidance article on finishing pistons and cylinders on Adrian's Model Engines web site.
And sorry, it may be normal for one or two folk on this forum to finally finish the job by lapping the piston actually in the cylinder using some kind of metal polish, but that is certainly not a normal technique.
And to say that an engine with a parallel bore will not continue to run or be able to restart is just plain silly and certainly untrue. I have a number of home built engines without tapered bores that have flown my vintage free flight models for many years. One of my earliest diesels built in 1987 is still going strong and back then I did not know much about tapered bores, it was good enough to make an engine capable of flying a model.
Ken Croft
 
Last edited:

Nibby2226

Member
Joined
Apr 5, 2018
Messages
10
Reaction score
2
My first engine was Boll aero too.
If you want made crankshaft with separate crankpin, i dont recommend use loctite.Crankpin must be pressed into web.Slide fit+ loctite leads to fail.Imo best option is one piece crankshaft.
It be better make cylinder with bigger bore diameter- bigger displacement is better :)
My first engine also. Great learning experience and so satisfying when it burst in to life and filled the workshop with blue smoke. I've now moved on to a Vega V twin on the road to attempting a Howell V4.
 

dethrow55

Well-Known Member
Joined
Dec 23, 2015
Messages
116
Reaction score
22
Location
texas
hello will be watching this build just before this virus broke out i started this build so far i have the crank case, but on hold for now, taking care of mom 100yrs old april 12.james
 

Mechanicboy

Well-Known Member
Joined
Jul 10, 2013
Messages
707
Reaction score
230
The important things to achieve when using this combination is that the bore should be tapered, wider below the exhaust ports. As a rule of thumb, the taper should be in the order of 0.0015" to 0.002" per inch of working stroke, but it's not that critical. In actual fact, it's hard to produce a fully parallel bore! So this set-up is ideal for beginners. Read this further 👉 Cylinder/piston Material Selection for Model Engines and the other about cylinder lapping 👉 How To Make and Use Cylinder Hones
 
Last edited:

dethrow55

Well-Known Member
Joined
Dec 23, 2015
Messages
116
Reaction score
22
Location
texas
hello here is another similar to bolero motor its called nelson 2cc .free download
 

awake

Well-Known Member
HMEM Supporter
Joined
Sep 4, 2019
Messages
734
Reaction score
219
Location
North Carolina
... so satisfying when it burst in to life and filled the workshop with blue smoke ...
I've had some of those blue smoke moments, but it was more alarming than satisfying.

Oh, wait, you're not talking about accidentally setting some shop rags or steel wool or wood shavings on fire? Never mind ... carry on ...

:)
 

Nibby2226

Member
Joined
Apr 5, 2018
Messages
10
Reaction score
2
:) - nope, more the rite of passage of bring your first engine to life and also noting that the next one will be started outside!
 

mr-mechanical

Member
Joined
Apr 30, 2020
Messages
15
Reaction score
9
Location
Cumbria, UK
Some very interesting reading. Thanks for posting.
Once I get to the piston and cylinder I will be reading all this carefully.

Some more progress made yesterday with the main / crank bearing made
IMG_20200601_185815_503.jpg
 

Latest posts

Top