There are 2 real reasons why you would do a rebuild. The first 1 is ideally the one that we will be choosing going forward however no 2 does happen periodically for a large number of reasons especially if we are ultimately trying to push engine performance boundaries! Also if you start doing this as a side hustle or for a living you are going to have people bringing 2 stroke engines to you for all kinds of reasons so it’s important that you understand.
- Routine maintenance – that’s right we have a certain number of hrs on the piston and it’s time to swap it out
- A problem has occurred with the engine:
- top end failure – seize
- loss of compression suddenly
- Gradual loss of compression
- Another engine problem
The easiest job to do is the routine maintenance job. Nothing has gone wrong. The engine still has good compression and runs as it should do and nothing has become damaged. We are going to replace what we have for new parts – that’s it.
A problem has occurred – now here is a whole world of potentials. To me after an engine problem it is likely that we will want to perform a full engine rebuild for which this is not the guide and you will need the 2 stroke full engine rebuild guide on phoenixmotos.com, however in a few situations we can get away with a simple top end rebuild. one of those cases is top end failure – seize. sometimes the seize can be light and sometimes it can be major (which would probably cause other damage) but if you can assess the situation and be certain that nothing has ended up in the bottom end then you should be able to get away with a top end rebuild. in the other cases:-
- Loss of compression suddenly and Gradual loss of compression – there is likely to have been something go wrong with the piston or cylinder. Some metal fragments will almost certainly have come away. You need to make a judgement as to whether the fragments could have ended up in the bottom end as if they have you need to be doing a bottom end rebuild as well
- Another engine problem – assuming it’s a problem which involves splitting the cases you are going to be in the bottom end anyway so therefore a full rebuild is on the cards!
Rule of thumb: if nothing could have got into the bottom end then you are ok to proceed with a top end, otherwise you need to rebuild the bottom end too. Actually doing the bottom end is not that bad and the more often you do it the more competent you will become!
Tools required – not including standard tools like spanners screwdrivers etc.
- Spring puller
- Torque wrench
- Torque adaptor
- Gasket scraper
- Set of picks
- Feeler blades
- Drill and 2mm drill bits – if there is an exhaust bridge
- Scribe – if there is an exhaust bridge
- Straight edge (metal ruler) – if there is an exhaust bridge
- Centre punch (I like to use an automatic centre punch) – if there is an exhaust bridge
- Blow torch
- Compression tester
- Fine file
- Piston ring compressor – nice to have
- Dremel with sanding drum
- Hot air gun
- G clamp