A.S.P. 'Series 3' .52 'S'

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A.S.P. 52 'Series 3' .52

A.S.P. 52 'Series 3' .52

Engine Test : A.S.P. 52 'Series 3' .52 Long(er) Stroke (RCM&E May 2003)

How does ASP's latest two stroke sportster shape up? Malc Pinnock gets intimate...

Along with this test I will try to give a few pointers on a safe engine strip for the DIY enthusiasts, or for who those of us who would like to try it but are not quite sure what to do, so read on and all will be revealed. But a word of warning however, any dismantling of a new engine will automatically void any manufacturers warranty and this applies to any make of engine, not just ASP.

The new kid on the block, ASPs latest engine [the .52’s] replaces the old 53. It has a slightly increased stroke and reduced bore over the engine it replaces giving increased power and torque at lower RPM. It is a very compact engine for its size, in fact no bigger than the average 40. So what's it like? Read on and we will endeavour to rip it apart.

Back Plate

Were do we start. First off lets remove the pressure die cast alloy back plate, this is retained by 4xM3 Allen capped bolts and is sealed by a plastic gasket. It fits deeply in the crankcase, and has a flat spot at the top for liner / piston clearance.

Cylinder Head

OK, up to the top of the engine to remove the die cast alloy head. (on a 6 bolt head undo the bolts like a clock; 12,6,2,8,4,10) The head is retained by 6xM3 Allen capped bolts and is sealed by a soft alloy head gasket that sits in a machined in recess in the underside of the cylinder head. The combustion chamber is of the modified hemi type, and is surrounded by a 4mm wide chamfered squish band. Centrally in the combustion chamber is the glow plug [std. long reach] tapping that has for the heavy handed amongst us been fitted with a brass insert? Die casting of both these parts is very crisp, with no flash or imperfections, and any machining that's been done, is also of a high standard.


Liner/Piston Assembly

Next job on the agenda is the removal of the liner/piston assembly, but first lets go round to the rear of the engine and scribe a small ‘x’ on the conrod, to aid us on reassembly. I also put a small mark centrally at the front of the piston crown, these marks ensure all parts, [in some cases pistons and rods are machined the same front and rear] go back together as they have been run and mated together. If you get re-assembly wrong, excessive wear will take place and some expensive spares will soon have to be purchased.

The liner in the 52 is quite a tight fit in the crankcase, so some heat was applied around the cylinder fins, from my trusty gas torch.[or put in an oven at 180-200deg for 5 to 10 minutes] not until golden brown like the naked chef? [Just enough to get the liner moving when the crankshaft is rotated]. Do not jam any metal objects in the ports to remove the liner, as this is instant wipe out. If you have to prize out a liner use a piece of softwood.

Right that’s the liner out, so it’s round to the rear to remove the conrod from the crankshaft. With the crankshaft at top dead centre [t.d.c] steady the piston crown with your thumb, and with your first finger on the bottom of the conrod gently pull backwards, on a new engine the fits are quite tight, so some care has to taken not to damage the bronze big end bush.

Do not try to remove the rod using pliers, as any marks on the rod will result in a weak spot that will cause the rod to break at high R.P.M. when run.

The liner / piston assembly is of the A.B.C. type, The liner is turned from brass with it’s internal running surfaces being hard chromed. It has a lip at the top for retention in the crankcase, that has a small vertical groove cut in it, for the steel locating peg that’s been pressed into the top of the crankcase, this ensures the ports are correctly aligned with the gas passages upon assembly. Porting is of the usual Schneurle type.

The large bridged exhaust port has an angled transfer port at each side and a single angled boost port at the rear opposite the exhaust, at the bottom the liner has been chamfered both internally and externally to aid fitting of the piston into the liner, and the liner into the crankcase.

Let’s now have a look at the piston and conrod assembly. The heavy-duty conrod has been CNC machined from high tensile alloy, and has bronze bushes for both the big and small end bearings. Both bearings are bored for lubrication, two holes for the big end and a single hole for the small end, and that rounds up the conrod.

The piston is pressure die cast from high content silicon alloy, with machining to it’s lower front skirt for flywheel clearance, and has a finely lapped finish to it’s running surfaces. Internally there are two large webs to support the fully floating hardened steel gudgeon pin that has been bored right through for lightness. The gudgeon pin is inserted into the piston from the rear, and is retained at the front by the piston skirt, that has not been fully bored through, with the same size bore as the conrod. Retention at the rear is by a wire circlip that is retained in a machined in groove.

A word of warning here, if you have to remove the gudgeon pin always replace the circlip, if a slightly bent one comes out when the engine is running, bye, bye, liner / piston. So a few pence here will save you a lot of bucks?


The remaining pieces to remove from the ASP, is the crankshaft and its ancillary's that consist of, a steel UNF prop nut, alloy prop washer and nicely turned wasted alloy prop driver, that has a machined in dirt shield for the front bearing, and the final part a steel thrust washer that sits between the prop driver and front bearing. Two opposing flats machined on the crankshaft retain the prop driver. Now these parts are removed, all that remains is to push out the shaft. This requires quite a firm push as it has a very good fit in the bearings, this is to prevent skidding when the engine is running. No need to belt it with a mallet though, just a good firm push between both hands will be enough.

OK, the shaft is now in my sticky little hands lets have a look at it. Turned from a single billet of chrome steel, Rear to front the shaft consists of a substantial 6mm-dia. big end pin, supported by a fully counter balanced flywheel. This leads on to the 15mm main shaft that has a very finely ground finish, and is cut with the angled induction port, that leads into the 9mm-gas passage. Moving forwards the shaft then steps down to a dia of 9.50mm for the front bearing. The final 6mm of this has been cut with the 2 opposing flats, for the retention of the prop driver, as mentioned earlier.

The final 30mm of the shaft steps down to 6.50mm. Of which the final 20mm are cut with a UNF thread for the prop-retaining nut.



A 40 sized crankcase, pressure die cast from alloy, with the cylinder liner and its transfer ports offset in the case, to keep the engines dimensions to a minimum size and keep the optimum size porting required for a 52 sized engine.

Looking at the case from the large exhaust port side, this has been bored at each end for the 2xM3 silencer mounting through bolts. Moving forward the front end is very stiff with 3 full axially running webs, 1 per side from the very substantial engine mounting lugs to the front bearing housing, and 1 centrally at the bottom running from the main case to the front bearing housing. There is a further web running from just below the exhaust port to the large carb boss, that has been bored through centrally from each side, for the 2xM2 carb retaining bolts and lock washers, the threads for these are tapped into the carb mounting spigot. The carb mounting boss also has provision for my preferred mounting method of the pinch bolt, but is left un-bored, this method would have been the better choice for the heavy handed amongst us, as stripped threads in light alloy carb bodies are costly to replace. It also allows you to swivel the carb a bit if required.

OK round to the other side, the cooling fins on this side continue down past the exhaust port to just above the machine polished manufacturers name plate, with the off set towards the front boost passage clearly visible.

Up to the top of the case we notice the quartic shaped cylinder fins, [A la Austin allegro steering wheel shaped] at the rear of the head is the single steel pin for locating the cylinder liner in it’s correct position, so the ports align with the transfer passages on assembly. The top of the case is also tapped for the 6xM3 Allen capped head bolts, and if we peer inside we notice the substantial offset transfer passages.

Round to the back door, With it’s 4xM3 back plate tapings. Looking inside we notice the machined in recess for big end clearance. And moving forward the 1st of the 2 smooth running ball races, the front bearing is of the single sealed type, this along with the dirt shroud on the prop driver should give good protection against dirt ingestion in the event of an unexpected meeting with terra firma. I do not remove bearings unless they need replacing. They are factory aligned and damage can be done to both crankcase and bearing if care is not taken when removing, or on re-assembly. That just about sums up the engine parts, so let’s have a look at the carb and it’s options.

ASP 52 Carb

ASP 52 Carb

A new carb (ala OS 4D) with a slightly larger venturi area, to improve performance. Twin needle, [choice of front or rear needle] with pressure die cast alloy body, fully sealed by rubber ‘O‘ ring, and fitted with an adjustable steel throttle arm. A very good ratchet for positive main needle adjustment, the main needle has been bored centrally for a wire extension and is fitted with an Allen capped locking grub screw. The steel throttle barrel has a chokebore of 8mm and the carb is very smooth in operation.

As mentioned earlier there are options for the carb. This is for either a front mounted main fuel needle or rear mounted safety needle. When ordering state your requirements.
Conversion from rear to front needle is easy; remove the whole <Actinic:Variable Name = 'blackened'/> needle assembly from rear needle holder, and replace it into the carb (by taking out the blanking plug).

My preference is for a front mounted needle as alterations are instant, but if you do go for the rear needle option, remember to allow a few seconds for the engine to settle.



The ASP 52 has 2 standard type silencer options; First off the quiet 2-piece die cast alloy type. This has an adjustable offset tail pipe, it is held together by a long central through bolt locking washer and ny-lock nut, and contains a very nice pressed alloy baffle.

The second option is for the super quiet silencer, similar to the first but with a turned bar stock alloy centre section. Both types are fitted with a chrome plated steel pressure nipple in the front body of the silencer, and the super quiet silencer option comes at a slightly price when ordering, and well worth the money when considering the neighbours who don’t like the noise, of the infernal combustion engine?

Just Engines also offer a full range of dustbin, Pitts, in cowl, tuned pipe or anything else we can dream up for the ASP and most other makes of engine, so please enquire when ordering.


The latest offering from ASP (the 52) is the third new high performance 2 stroke this year, alongside the much improved .40 and .46 (with a new compact .91 due out by the time you read this).
A very compact well made engine, with increased torque over the old ’53’ due to the increased stroke to bore ratio.

Very easy to start and adjust, in fact just a couple of flicks straight from the box. The test engine was run in on Flair Yellow Spot 20% Castor /5% Nitro. Castor based fuel is my preference for running in as it gives a new engine more protection against a lean run, After 1hours running in I then change to synthetic oils, or a synthetic/castor mix as In the 52s case. Flair Yellow/Gold a 10% synthetic 5% castor mix, with 5% nitro. ASP aero engines are timed for 2% to 5% nitro, so large doses of nitro will not improve the engines performance. It will just make the engine hard to set and possibly lead to internal damage, due to the pre ignition caused.

And just for the folks who want to know what it performs like in the air, bolted to the front of my Flair Lark, Vertically like a rat up a drain pipe?

And just for the wag down the field A.S.P. does not stand for [all spare parts] I think not? After this test Affordable Stunning Performance is probably more accurate!

Anyway back to the test, for less than a hundred quid this has got to be just about the best performing of the ‘sport’ engines available. Easy starting, easy to tune, and in a casing the size of the OS40FX, with the same bolt / bearer and OS Exhaust port spacing, giving you bags of silencer / pipe options. The Re-designed and re-timed ASP 52 offers excellent value for money, and just in case of that whoopsy spares are readily available. In my opinion this engine offers stunning performance at a very affordable price.

Data File


CONFIGURATION Single cylinder 2 stroke, ABC liner/piston with schneurle porting and twin ballraces.

DISPLACEMENT .52 cu. ins

BORE 22.4mm

STROKE 21.5mm

STATED POWER 1.75hp @ 17,000 rpm

WEIGHT inc. super quiet silencer 500g

SUPPLIED WITH Silencer & gasket, 1x allen key, full English written instructions.

2 Year warranty. Please state your option for carb and silencer when ordering.

Running in: Flair Yellow Spot 20% castor 5% nitro.
Test: Flair Yellow/Gold 10% synthetic 5% castor, 5% nitro.


AVERAGE NOISE TEST AT 7mtrs. Quiet silencer 82db


11x6 Radio Active (RAM) 2.400 13,400
11x7 RAM 2,400 12,800
11.5x5 Bolly Clubmans 2,400 14,400
12.25x3.75 APC 2,200 13,200
12x6 RAM 2,200 12,000
12x8 APC 2,200 10,000
13x6 RAM 2,200 10,400

and on a follow up test (due to popularity of prop)
13x4 APC 12,600

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