Thornycroft problem

paulg

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This 35hp thornycroft 90? has been stood for ages when we bought the boat.It,s 1985ish.Would not start.Did injectors,changed fuel/filters/bled system/bypassed filtersetc etc.Fuel pump has govenor sitting on top and the housing that holds the top bleed screw has come loose.It was "glued"in.Do I have to remove the whole unit or can it be epoxied back together in situ.Got it fired up today,at last but pressure on the part affects the running.Does any one know what I'm trying to describe?i

paul
 

chas

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Yes I do! I have the same problem. Mine came loose at the beginning of the season and I put it back in with gasket cement and wired it down with Monel wire. It has lasted to date - starts well but idles too fast. Apparqantly there is a replacement top cover for the pump which costs about £27. I spoke to my local Lucas CAV depot and they have offered to recondition the pump for me. When I described the problem, the fitter (who was not a young man) said "I have heard about those but never seen one"!

Best of luck!
 

brianhumber

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Sounds like the same engine as was in my old UFO. If my memory is correct this was a marinised version of a BMC engine. The injector pump is a CAV DPA rotary instead of the more well known in line or single cylinder units. I cannot remember bleed screws on the top, the distributor body and control cover bleed screws being on the side of the pump. There was a relief type valve on the top which was normally factory set. The good news is these pumps are still available as the engines were fitted in all sorts of Vans, landrovers, pumpsets etc. Try Automarine Diesel Sevices in Hove.
 

paulg

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Hi thanks for the response it's cheered me up no end.The engine is in a UFO34 which I'm in the process of rebuilding internally so if you know anything you think may be useful I/d be grateful.Original owner has moved the DECK stepped mast onto the main bulkhead ,well supported but I don't know yet how it will affect balance.The engine part we discussed is indeed a relief valve which I will re attach .It will get the boat the 50miles to here(with a bit of luck!)and then we can do a proper job.Was there supposed to be an O ring around the relief valve do you know?
Paul Gretton


paul
 

brianhumber

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Can't recall the DPA having rubber o rings I would suspect a diy job. No need really as the DPA is still supported CAV service agents.
If the engine and thus boat has not been used at sea for some time I would suggest you try to drain off bottom of fuel tank to check for any water or sludge, if you find sludge you must get rid of this before using at sea, finest fuel filter blocking agent known to man. Take plenty of filter replacements when you make your 50 mile trip.

I found the UFO a very stong seaboat. Am a little puzzled by your deck stepped mast as mine had a keel stepped mast with a balsa coachroof that would not take the compressive stress of a deck stepped mast. I had to reinforce the balsa in way of the front cabin/saloon bulkhead as it had gone soft through the GRP cracking. Also check your rudder, my internal lugs completely rusted away from the stock leading to movement of the blade independant from the stock. The moulds were still at the builders yard north of Wroxham in Norfolk so it was not a problem to get a new blade moudled onto the stock.

Good sailing
 

chas

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As far as I can rememeber, there is a small O ring between the lower (locking?) nut and the disk that has come out. The "bolt" that screws into the disk is hollow and has a smaller bolt in the top. This seems to the the bleed system. The slow running or stall adjustment is the larger bolt held by the locking nut. Until I managed the fix the disk back in firmly, my engine used to suddenly rev up (at about 20 min intervals), going from about 1500 rpm to 2500 rpm. If you enounter this, just push the disk back in. I hope this makes sense! It never stopped, though, if that is any comfort.
 
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