Zac Posted December 22, 2018 Share Posted December 22, 2018 (edited) I bought a used Hpi Bullet MT 3.0 for what I thought was a good price but im having a problem with it. Sometimes when I let off the throttle from anywhere between 50 - 100% it cuts out. I first thought it was just the tuning, so I reset the needles to factory and idle to 1mm and re-tuned from there to no avail. Tried replacing glow plug to os No.8 still dies. So I sealed the carb and backplate with rtv sealant, went to try it out the next day but then the pullstart spring took its last breath. So I took off the cylinder head now fearing low compression and found the piston and head button with corresponding pitting as if there has been some kind of debris in there. The sleeve feels smooth all the way round. I don't know what to do please help. Here is what I found. https://ibb.co/stKMTjf https://ibb.co/GcCrnT4 Edited December 22, 2018 by Zac Quote Link to comment Share on other sites More sharing options...
Fly In My Soup Posted December 22, 2018 Share Posted December 22, 2018 Had three hpi 3.0 engines.....all three had head button failure...all three due to stripped/worn threads from glow plug changing after around 6-12 months... Get a new head button...I had real issues finding one around two years ago... But that was around the time hpi had financial difficulties Quote Link to comment Share on other sites More sharing options...
Zac Posted December 23, 2018 Author Share Posted December 23, 2018 10 hours ago, Fly In My Soup said: Get a new head button...I had real issues finding one around two years ago... But that was around the time hpi had financial difficulties I can get a new head button, but what about the piston and sleeve? I don't know how many gallons has been through it, and as I've not completely stripped down the engine I don't know what compression is like. Quote Link to comment Share on other sites More sharing options...
Wraithstorm67 Posted December 23, 2018 Share Posted December 23, 2018 Don't forget to check the clutch spring hasn't failed they are quite weak I upgraded mine to a 3 shoe clutch so much better Quote Link to comment Share on other sites More sharing options...
Fly In My Soup Posted December 23, 2018 Share Posted December 23, 2018 2 hours ago, Zac said: I can get a new head button, but what about the piston and sleeve? I don't know how many gallons has been through it, and as I've not completely stripped down the engine I don't know what compression is like. Yes the piston head is pitted somewhat... But at this size of engine it shouldn't really affect running or compression as the pits are contained within the circular head and not on the edge. Go grab a head button and rebuild...then try Quote Link to comment Share on other sites More sharing options...
Zac Posted December 23, 2018 Author Share Posted December 23, 2018 24 minutes ago, Fly In My Soup said: Yes the piston head is pitted somewhat... But at this size of engine it shouldn't really affect running or compression as the pits are contained within the circular head and not on the edge. Go grab a head button and rebuild...then try ok I will try that, but the pitting is on both the button and the top of the piston and the threads look fine on the button. Quote Link to comment Share on other sites More sharing options...
Fly In My Soup Posted December 23, 2018 Share Posted December 23, 2018 Has it been shimmed properly? There should be a few brass shims that form the head gasket. When it was built up..... Could you hear a hiss before the pop of the engine turning over ....e.g when you pull the pull start slowly out......you should hear a clean pop pop pop.....if it went hiss pop hiss pop hiss pop then its defo an air leak.... I can only give advice as per my own findings with three of these hpi engines.....without having it in my hands....its hard to pinpoint why an engine won't run properly as there are so many variables Quote Link to comment Share on other sites More sharing options...
Zac Posted December 23, 2018 Author Share Posted December 23, 2018 (edited) Im in the process of stripping it down now, there are 2 brass shims. I don't think there was an air leak but i did seal it. there seems to be no pinch but I cant get the sleeve out. Edited December 23, 2018 by Zac correction Quote Link to comment Share on other sites More sharing options...
Fly In My Soup Posted December 23, 2018 Share Posted December 23, 2018 Is the piston stuck in the sleeve? Take the heatsink off, take the manifold off, Heat the outer casing with a hairdryer/heat gun/blowtorch in circular motions round and round the outside of the casing (not the piston itself)..... Pour 3in1 oil on the top of the piston head and some on the underneath off the piston (access from the exhaust port) Wear gloves, its stinky...and hot.... And pull with moderate force on the pull start......when it's heated nicely. Repeat until free If you don't mean the piston is stuck in the sleeve, you mean the sleeve is stuck in the casing....then you can use this same method to free it....heat and oil....but instead of using the pull start... Pop it in a vice and use a tool to tap it free...I used to have a purpose made ( diy bodge welded ? ) tool for sleeve removal Quote Link to comment Share on other sites More sharing options...
Vr5fx Posted December 24, 2018 Share Posted December 24, 2018 On 23/12/2018 at 12:24, Zac said: Im in the process of stripping it down now, there are 2 brass shims. I don't think there was an air leak but i did seal it. there seems to be no pinch but I cant get the sleeve out. Cabletie between the top of the piston and the exhaust port on the sleeve, gently turn the flywheel and the piston will push the sleeve up with the cabletie. Then you can ease the sleeve out. Quote Link to comment Share on other sites More sharing options...
Zac Posted December 25, 2018 Author Share Posted December 25, 2018 21 hours ago, Vr5fx said: Cabletie between the top of the piston and the exhaust port on the sleeve, gently turn the flywheel and the piston will push the sleeve up with the cabletie. Then you can ease the sleeve out. I have tried this, its well stuck in there. Quote Link to comment Share on other sites More sharing options...
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