Hi folks! I has repaired the OS Max 10 FP and got the engine to run as a new engine.

I maked the new sleeve who are higher than old sleeve with contrapiston added inside. Sleeve are made of torsion bar from old car, the piston and contrapiston from old camshaft. Used 2 screws at cylinderhead only. Cause the treads in crankcase are damaged of early owner when he tried to fix the treads.

The engine ran 11500 rpm with 8x3 propeller.

No way back to glowengine again.

Jens Eirik

Nice job Jens, ohhhhhhhh for a lathe.

Hello Jens,

I have one 10FP on my bench for conversion. Thought about getting a davis head (im kinda lazy i guess) , but why not make one myself after all.
Question, what did you use as seal for the contrapiston ? A hi temp o ring ?

BEst regards,

Franck

The contrapiston lapped and mounted thight in the sleeve, but can be moved of compression and without leakage.

Also nothing contrapiston in the cylinderhead, the cylinderhead are to hold the sleeve at place in crankcase.


How i did with new sleeve and piston:
The sleeve was lapped first before the piston lapped a bit tight until exhaustport in the sleeve + lapped through sleeve with chrome polish pasta. The sleeve must be tapered to keep compression while piston are raising to top of dead centre.

How to control after lapping are finished:
Without oil the piston moves tight in sleeve and with oil will piston move light in sleeve + loose in bottom of sleeve and tight in top of sleeve.

Jens Eirik

THanks Jens for your explenation.

I know the technique of lapping, but have not mastered it yet on my lathe
I will make a head with contrapiston and O-ring instead.

Still puzzeling what engine i should use on my latest project a no-cal F8f. The 10FP or the Magnum XL15 (both _to be_ converted to diesel)

Best regards,

Franck

It is not difficult to make contrapiston without O-ring..

Lap the bore (sleeve) to all marks of the tool are disappeared. Make the contrapiston who are 0.1-0.15 mm bigger than bore. Lap the contrapiston sometimes and try to fit the contrapiston in the bore, it must be pressfit. If you can not press with finger and do it possible to press with drillpress or tailstock at lathe, some time with force of hand, all are ok. Not halfpress or loose fit!

Read here how do:

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.

Jens Eirik

Thanks Jens for your explanation !

I found this website too, lots of information.

http://modelenginenews.org/

I am going to do more on enginebuilding this authum and winter. I'd like to buy a complete "new" set of equipment. Still trying to find out what i need...
so much to choose.......

http://www.buitelaar.nl/

I made some progress (without lapping, sorry jens) and made a quick and dirty head with high temp O-ring (from a 4-stroke kawasaki valve) for the FP. The engine is a bit dusty and dirty, will clean
her up later this week. Engine has a nice compression, no leaks. Have to make me some new fuel first.