Part two sees the engine stripped.
The Honda SS125’S motor goes under the surgeon’s knife. Steve Cooper passed the forceps and took the pictures.
in our first instalment of Project SS125 Honda the bike had been broken down ready for a total overhaul. Owner, Peter Spence, has already told restorer, Andy Jones, that he’s determined to use the bike the way Honda intended and that means it’ll be worked hard. So, it’s likely to be spinning its crank at ten grand plus speeds at some point its life. Now we know these bikes are well engineered but who in their right mind would be beasting an unknown engine this hard? The bottom end is a robust roller bearing assembly and should be very reliable but if something lets go how easy is it going to be to find new crank parts? Exactly and with that in mind the engine is off to see Dr Dave Jupp in his Home Counties surgery: gloves on, tools out and crank up that camera Scoop!
2 5 5/ Cover off and clutch actuating mechanism revealed on the inside of the case. Surrounding the cam on the end of the crank are the two arms of the advance/retard mechanism. 6/ The rotor has been pulled off the crank with correct tools and the stator unbolted. The insulation and wiring of the latter will be inspected for damage later. 7/ Inner cover removed the cam chain tensioner to the right of the chain and its adjusting rod are visible with the jockey wheel to the left. There’s also some evidence of blue gasket material at the crankcase joint.
8 8/ The camchain leads a relatively easy life and so it’s fitted with a simple split link which makes the next job that much easier. 9/ With the cam sprocket removed from the camshaft it’s now possible to remove the cam chain and prepare to lift off the cylinder head. 10/ Just a few gentle taps and the cylinder head is off. Apart from some carbon build up all looks good. Note the hollow metal dowels on the head and barrels; we need to make sure they’re all accounted for. 3 2/ The top engine mount now needs to be undone as it is fixed to the studs that run right from the top engine case, through the cylinders and up through the cylinder head. 3/ The mount also acts as a baffle and breather system for the engine. Our first look inside the motor here shows no build up of oil/water condensate, which is encouraging. 4/ With the cover off on the left-hand side we have access to the points and condenser. The peripheral crosshead screws need to be removed to gain access the generator system. Note the timing plate which looks like many two-stroke systems. 4
11 11/ The cam followers or tappets and their respective spindles are zip tied together; red for exhaust, green for inlet. The camshaft itself is simply a snug fit on its mounts. 12/ The camchain’s rubber wheels are removed and checked for damage. High running temperatures and old oil rarely do synthetic materials any favours. 13/ With the base nuts removed the barrel is lifted clear to reveal two remarkably clean standard-sized pistons. This confirms our suspicions that the engine has seen little use since a rebuild some time in its past.
14 14/ And here’s further corroborative evidence. The original cross hatching of the factory hone can still be clearly seen so whatever happened to the motor it wasn’t a seizure. 15/ Whoever went inside also cleaned out the centrifugal oil filter as the few pieces of crud in here certainly don’t line up with the bike’s documented mileage! 16/ Over on the other side of the engine the side case is off. More evidence of blue silicone gasket sealer and some vile brown sludge in the bottom of the side case begin to raise concerns. 17/ With clutch plates removed the basket is lifted off along with the oil pump which is driven via a bell crank off the back of it. There’s more brown sludge in here as well. 13
The plan now is get everything cleaned up, measured and checked ready for the rebuild. We’ve already picked up on the fact that the valve stem oil seals have gone hard and these were probably letting oil seep by into the combustion chamber. The good news is that the crank is in top shape. It’s been said before but it still holds true; providing these early Hondas are kept fed with fresh, clean oil they are likely to run for years. The pistons look like they have seen minimal use and there’s no evidence of blow-by so tolerances must be good. Also the rings are still amazingly springy, again suggesting little use. Admittedly the piston crowns are heavily carbonised but perhaps the dead and diseased air filter we saw in Part I may well be the reason for the apparently rich mixture. Whatever, the carb will need a looking at as well just to make sure. So, why was the engine taken apart and rebuilt with blue silicone sealer? Well, with a blend of circumstantial evidence and informed supposition there’s a theory. Given the sooty piston crowns perhaps a previous owner surmised the bike was burning oil and this, allied to a possible oilseal leak, trigged the so-called overhaul. The cases were taken apart to sort out the seals (the ones in place all look quite fresh by the way) and a set of new standard pistons and rings were dropped in for good measure. The grungy gloop in the bottom crankcase needs to be cleared, but once done we’re ready to rebuild the motor. Stay tuned!
1 1/ Starting on the top end the long bolt that passes through the cam and holds on the cam sprocket cover is removed allowing us sight of the cam chain.
18 20 18/ This says it all; blue silicone gasket sealer oozing out between the upper and lower cases. However, we’ve yet to determine why the engine was previously taken down. 19/ With all the bolts removed the cases are carefully tapped apart liberating the crank and transmission. There’s loads of silicone evident along with some high-quality crud in the bottom of the gearbox casing. 20/ Nothing obviously wrong here upon first inspection: the crank is a pressed-up item and typically over engineered. Honda was aware these bikes would get worked hard; none of the bearings are exactly small.
21 21/ The gear selector drum carries some evidence of mild corrosion, which is possibly consistent with damp storage, but it’ll be easily cleaned up. 22/ Disgusting: there’s no other word for it. This stodgy oily porridge is incredibly thick and tenacious. It’s been there for years; why wasn’t it removed when the engine was apart? 23/ Using a twin-forked spring compressing tool the valve caps are pushed down to facilitate removal of the collets. The cylinder head is amazingly petite and compact. 19
24 24/ And there are all the components stripped out of the head. Again nothing looks like it has seen particularly hard work and everything should clean up fine.