Good work Ian.... Great explanation! regards Rob Rob Thompson 0429 493 828
On Tue, May 30, 2023 at 3:24 PM Ian WIlliams <[email protected]> wrote: > Hi TMG team, > > Rob I hope u don’t mind me responding as well. Here in NZ we have to have > the mag bench checked every 2 years and I look after 2 coming up 3 Dimona’s > and 2 Grob 109’s so do this job with monotonous regularity. > > My procedure is as follows. > > - Disconnect battery > - Remove the right hand Carb (from the front) and disconnect the choke > and throttle rods. > - Disconnect and remove the starter and remove spark plugs > - Turn the engine so cyl *1 (The front right hand side one) is top > dead centre on its compression stroke (Finger over the spark plug hole) > - Note the little mark on the prop flange … it is set to 25 degrees so > wont line up with the case centre seam at TDC .. it is used for retiming > the mag > - Use a long allan key and undo the 2 clamps attaching the Mag … the > Alternator bracket and probably the throttle bracket are also attached so > note how they are connected. I keep the bottom alternator bolt tight so it > doesn’t move slackening off the belt. > - Pull out the mag and remove the rear cap with the 4 HT leads (3 > screws) > - Get the Mag serviced > > Back on > > - The Dimona Mag is Right hand. So get a pin (an unused pop rivet > works well) Look at the back of the mag and u will see 2 holes. Use the > one marked RH Put the pop rivet into it and slowly turn the input until > the rivet shaft slips right in. The mag is direct drive but has a 2:1 > reduction inside and the pin / hole is in the smaller gear so u may have to > turn it twice to make the pin go fully in. > - Now the tricky bit. I use a length of masking tape crossed over to > secure the impulse in a fixed position but in such a way that once the flex > coupling is almost in place the masking tape can be pulled out. THEN > REMOVE THE POP RIVET then reinstall the rear cap and the 3 screws > .. note there is only one way it can go on. Taking care not to dislodge > the masking tape. > - Now Double check Cyl*1 is at TDC. Offer up the mag and the gasket > as Rob has described. Be real careful here. You can see the coupling > through the Alternator belt slot. With a torch. Once it looks as if it will > slip in OK, remove the masking tape and reinstall the 2 mounting clamps but > don’t tighten just yet. > - Make up a small “buzzer”. I use a real cheap electric ceramic > buzzer (about the size of your finger nail and a 1.5 volt AA battery) > Write it up and use 2 flying leads with clips at the end. Check that when > you join the clips together the buzzer makes a noise. Connect one clip to > the “P” lead on the mag and the other to ground Now rotate the prop around > the TDC point. You should hear a change of tone on the buzzer when the Mag > points change state. It is not much of a tone change but is clearly heard > - Now identify the mark on the prop flange and rotate the prop around > it listening for the change of buzzer tone. Adjust the mag position so > when rotating the prop in reverse (ie taking up any slack in the drive) the > change of tone happens exactly when the flange mark is lined up with the > split in the case halves. > - Once you are happy tighten the 2 mag retaining clamp / bolts > - Then slowly rotate the prop through all compressions and note the > spark should correspond with that cylinder on its compression stroke The > firing order is 1 3 2 4 ie 2 bangs on one side and 2 on the other. > - Because of the impulse of course the firing spark is quite retarded > when turning the prop manually and is roughly at TDC. This is a good way > of confirming u have it correct. > - Then put the leads back on the mag, reinstall the starter and Carb. > And of course the plugs and battery > - All should then make the usual noise . > > I hope this is of some help > > > > Best regards > > > > Ian Williams > > ZK-GCB > > > > > > PS… Is anybody else having big issues with Hoffmann propellors ?? > > > > *From:* [email protected] <[email protected]> *On > Behalf Of *Rob Thompson > *Sent:* Tuesday, May 30, 2023 9:38 AM > *To:* [email protected] > *Subject:* Re: [DOG mailing list] Magneto removal. > > > > 1 Line up the engine at the timing mark firing on #1 cylinder. > > > > 2 Remove the engine control rods and starter motor so you have room to get > the magneto out and back in again. > > > > 3 Take the cap and harness off using a right angle screw driver. I > replaced the slot head screws with Alan screws to make the job easier to > refit the cap. > > > > 3 Loosen the magneto bolts with a long Alan key. I welded a long Alan key > to a 1/4 inch socket and then used a small ratchet spanner in behind the > magneto. > > > > 5 Follow the magneto install instructions in the manual. *It is important > to get the gasket measurement right or the magneto may FAIL.* You can do > a trial fit with plasticine or Blu Tac which compresses against the > flywheel and then measure that you have the right clearance. > > > > regards > > Rob > > > > Rob Thompson > > 0429 493 828 > > > > > > > > On Tue, May 30, 2023 at 6:22 AM Tomasz Dzikuć <[email protected]> wrote: > > Dear Dimona users. > > > > The date of inspection of our magneto is approaching. > > > > The information I found on this list shows that the removal of the magneto > can be done without disassembling the entire engine. > > > > Unfortunately, we don't know how to do that. > > > > Does anyone have any short instructions on how to do this or just can > write some tips here. > > > > Thank you in advance and best regards from Poland. > > > > Tomasz Dzikuc > > > > TMG Team > > AZL Zielona Gora > >
