TT Redline 53 Crankshaft Query

[philjac94]

Can someone comment on the following? The engine has only just gone through its break-in. Bearings are in perfect condition.

Engine crankshaft axial clearance (endfloat) excessive, measured (0.3mm) with fan hub installed and thrust washer fitted. Pulled the engine apart and re-measured, sure enough in laymen terms the crank is too long for the crankshaft housing by 0.3mm. This is never good (in my mind) as this allows the whole crank/clutch/fan assy to move, also, within the engine the conrod bigend/journal & little end/gudgeon relationship alters by this 0.3mm. This was also seen on the backplate, I could rotate the engine while pushing rearwards and hear the bigend journal touch/scrape the backplate. The solution is to either regrind the crankshaft bearing landing or shim the front bearing. I did the latter using a standard 22/16mm wave washer these are 0.25mm thick. The remaining 0.05mm is taken up by the "wave" giving a soft preload. The result is no axial displacement and both bearings equally softly loaded, with still enough room for expansion once at running temp. I don't know which item is wrong as i don't have machine drawings or maybe TT designed the engine that way on purpose but i cannot think of any purpose for allowing an engine to run on the backplate for axial restraint.

[Grant_beltcp]

Are you sure you put the fan hub assembly on all the way?
I had to take off the back plate off the engine and lock the shaft up and push it all the way in when i put the fan hub assembly on. If you do it that way it gets rid of all the play and stops it rubbing on the back plate.
Atleast it did with mine.

[philjac94]

It was positively home, like i said even when measured ther was the same difference.
Ran the engine since mod and sounds great. Hopefully mine was a one off. Hate to think what a major recall would cost TT. Would be a touch worse than their carby recall.

[murp]

I just bought a used TT53 and while I was installing the fan hub I noticed that the backplate had gauges in it from the conrod journal just as you described. I believe some metal bits from the backplate caused the scoring I see on the side of the piston. Unfortunately I have no way of repairing it - is there anywhere to buy replacement parts for this motor?

[philjac94]

Parts are readily available for this motor, In Australia anyway. It would have to be a fair size slither of metal from the backplate to damage the piston. How deep or severe is the scrape. More likely cause is the glow plug element which detaches when leaned/burnt out. While its apart i recommend fitting the 22/16 wave washer if the end float is excessive. Works a Treat.