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Reverse Gear Problem

I have a 2011 20hp four stroke with remotes. I cannot engage reverse gear mostly (forward is fine) but when it occasionally engages sounds as if it is slipping with a ratchety noise. I last used the boart 2 years ago now when there was an emergency situation and I needed to slam the boat into reverse a few times and I might have damaged the dog clutch. The cable adjustment is fine and all line up in neutral; I have also tried adjuting the cables to the limit without any improvement. The lever operated by the cable on the engine seems to be moving to the fwd, neutral and reverse positions ok I am going to have to go and take it apart in a week or so but the lead time on parts can be quite long here in the UK for Tohatsu parts so I am trying to best guess parts to order beforehand. I am thinking new dog clutch, sliding pin and pin retaining spring circlip and a new O ring water seal for the hub. The motor has only done 400 hours. The workshop manual is on the boat 250 miles away so I am thinking a bit blind here. Should I need any other parts to get this engine going again. I want to fix this quickly to retrieve some sailing in this strange covid year. My engine and transmission diagnostic skills are not bad so I am assuming that I have got this right but is there anything else it could be?
 
I assume you have an MFS20C. Year is irrelevant. Verify you are fully engaging the cam into reverse (down all the way). Consider that if the clutch dog is damaged, the reverse gear may also have damage, and the bits flowing with the lube can eventually damage the bearings and the teeth of the gears.
 
Thanks for reply pv... Yes MFS20C. I have not used the boat at all so hopefully no consequential damage due to bits in the oil. The shift rod seems to go to the upper and lower marks relative to the guide bush. Is there another way of checking this?
 
Thanks for reply pv... Yes MFS20C. I have not used the boat at all so hopefully no consequential damage due to bits in the oil. The shift rod seems to go to the upper and lower marks relative to the guide bush. Is there another way of checking this?
 
It is disappointing to find that (in uk) all the parts I might need are not in stock in the UK - delivery up to 5 weeks from Japan? So much for trying to retrieve some sailing in this difficult year. Stay safe.
 
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