Broken camchain tensioner

[Richard K]

Dear Forum, I had a good day and have dismantled by non running Jota with all the bits that need to, ready to go to the powder coaters. Satisfied with with my endeavours, I have set about the engine and subsequently had a fairly disastrous day and as a consequence I am looking to you all for salvation. Firstly, I had anticipated doing a top end overhaul of the engine and planned to stop north of the crankcase. I was taking the cams off when the half moon shaped doo hickie that holds the cam shaft in place dropped off mid disemmbly and dropped into the only FUCKING hole in the garage that would have caused me so much pain- which was right down the cam chain passage and into the bowels of the engine. Anyway, I have a magnet on a pole and so went fishing for it. I got a bite and thanked the lucky stars only to discover it wasn't that but the broken half of the cam chain tensioner, that at some point prior to my ownership has obviously parted company with it's upper end (which was still held in place by the retaining bolt. I also noted that at some point, the now liberated camchain has started to bite (about a mm) into the crank case. The damage that was sone to the crankcase looks sufficiently trivial to not cause problems. So now my dilemma. Do I go into the bowels of the engine to try to find any damage down there ? Or do I trust to good luck and hope that the half moon doohickie can float around in there in perpetuity and that the broken half of the cam chain tensioner has done no harm in there. Thoughts please. Oh and for good luck, I am also asking- while I am this far in, what would anyone replace ? The head looks spotless, the barrels are as smooth as a babies bottom and the rings looks fine, I havent had it running yet, but it turned over nicely before I dismantled it.

 

[mcnicol]

Richard, the chances are more than fair that if you take the bottom cam chain guide off from the bottom crankcase and reach in and feel around, you'll quite likely find the cam bearing locator stuck in the sludge in the bottom of the bottom case. So don't go flailing the motor around too much until you've retrieved it.
And if that doesn't work, you have the motor so far apart at this point I would be very tempted to go ahead and see what else the DPOs have left in there, plus check bearings, replace seals etc.

Ken

 

[Richard K]

Thanks Ken. Incidentally, I have 77JOTA on a California plate

 

[sfcpiet]

Camchain tensioner blades often break due to getting a right hammering from too loose chains.  Witness marks at the crankcase mouth as well as around the main bearing support in the crankcase are also quite common, but nothing to worry too much about.

Check top ring clearance in the ring groove.  Piston usually looks fine, but the up-down movement of the ring turns the engine into a giant high-powered oil pump, spewing oil out the breather once the revs top 6000-6500.  New pistons are the only way out, or you spend ages looking for wider rings and somebody willing to machine the grooves to suit.  The factory actually specified new pistons in the course of normal servicing at 65000km for the RGS models, to counteract the phenomenon.

piet

 

[Richard K]

Thanks Piet, I just invested in a micrometer and so will be doing some thinking and some sums.