Hitchcocks Forum

A 2 stroke crankshaft question, if I may. It’s not Royal Enfield, but I am a Royal Enfield owner and this is the best forum I know of, so hopefully it may be acceptable. It could have been any 2 stroke engine, really. But to the point: .-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

I have a Sachs 175 cc 2 stroke that has done only 10000 km (approx. 6000 miles) since new in 1966. I know that is the genuine mileage, as the bike is an ex military, Norwegian made bike that has spent most of it’s life in storage, probably waiting for some war that luckily never came. As a result, the bike is “like new” in many ways, and definitely not tampered with in any way. I have had it a couple of years, ridden it only a few hundred km.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

There is however a metallic rattling or knocking in the engine, that I don’t like and can’t remember from a similar, more worn engine I had some years ago. On idle and on overrun it is sort of a high pitched rattle. When accelereating or going uphill at moderate to medium high rpm, i.e. giving the engine some load, it disappears. It is not easy to describe it exactly or pinpoint the source, as both the air intake and the exhaust is fairly noisy. Last Saturday I finally figured out this “test”: I engaged top gear (4th) and pushed the bike along, to exclude all noises but the engine rotating. There is a definite “knock” every time the piston passes tdc. This can’t be good? .-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

I think this may sound like a problem with the crankshaft bearings (an M20 roller bearing on each side) or big end bearing (a roller bearing). Can that be the case? In case, I hope for the main bearings, as they are far easier to renew .-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

As this is a 2 stroke, there is no engine oil to collect metal particles from worn bearings. Fortunately it is easy to take the head and cylinder off. Then I will probably be able to feel it if there is too much play somewhere. .-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

I can mention that I have had the head off for a decoke, but it wasn’t much at all to remove. The clutch and gearbox works just fine, there was just the tiniest traces of extremelu fine metallic particles in the gear oil etc. etc., so I can almost for shure rule out most other possible causes. .-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

I wonder how the main bearings or the big end can break down after only 10000 km, but I guess the combination of very little use, many years of storing, no engine oil and small amounts of moisture/water may cause corrosion and bearing failure. .-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

Anyway: I will have to investigate this during the winter. Probably I have to split the engine and change some bearings. Or may there be something else that I have completely forgotten? .-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

Regards, Anders F. R.

Hi there, ANDERS ----------- might be able to offer some practical help on this one. First---SACHS are the worlds' oldest motorcycle manufacturer --- but hopefully it's not been in store THAT long, ?? They made some 175s in the '50s and '60s that look very much like the BSA Bantam so I'm assuming it's one of those. I prepped. and raced 2-stroke Grass-Track bikes back in the mid-'70s when the BSA C15 and Baracudas' were being totally outclassed. I started with a 250 Bultaco and added a 350 Montessa later on, both being 2-stroke singles with roller bearings everywhere !!!----------- OK, to business then. To be frank there should NOT be any noise from the engine at anytime. However as these engines are about as simple as any reciprocating engine can get then it's not going to be any great probs for you to work on. From your v.good description my first instinct is either the small end OR rings, possibly--and this is so simple to check by stripping down to the crankcase............. Long-term storage with any machine has it's own, unique problems eg}--- was it "Laid-up" properly to start with ?? Just because it's Ex-Military is no guarantee. ( My last job pre retirement was 15 years with Military Engineering).......... Is it a vertical split or Horizontal split type ?? If horizontal then LUCKY YOU !!---eazy peezy stuff (Both mine were--- Starting on a Friday eve. then a full strip, repair and re-build, back into the frame AND racing again by the SUN... Winning, did you ask ? AHHH, we'll talk about that at a later time, eh ??

Doesn't sound like main or big end bearing to me. If it was the big end then I would have thought it would be more pronounced under load than disappear. A mettalic rattling sounds more like a broken ring assuming there is nothing simpler like a too long reach spark plug clipping the piston on TDC?

I would say it is most likely to be the following very common two stroke engine faults:....1) Stuck piston rings that have carboned up in the piston grooves....2)Small end bearing wear.... 3) Piston slap, as often the piston can wear very quickly on a two stoke if the pre-mix petrol oil ratio is too lean. 4)....I would not rule out big end wear either, but least likely....not likely to be main bearing wear....BUT some European bikes used main bearings with nylon cages that broke up after becoming brittle from the effect of the two stroke mix....very common on MZ's

Thank you, all of you, for quick and informative replies! -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-. Alan R.: Yes, it is one of those "standard" Sachs 175 made from the early fifties until the late sixties. Shaped almost like an egg with a cylinder on the side. Nice looking and known to be reliable as far as I have heard. Unfortunately it is split vertically. I have dismatled and assembled two of these engines earlier, and it's not too difficult as long as you only need to deal with the engine part of it. Just be careful not to disturb the mainshaft and layshaft and loose a lot of small bearing rollers on the "wrong end" of those. That is almost impossible to sort without dismantling the gearbox completely as well. Don't ask me how I know..... You are right about not knowing HOW it has been stored. -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.

Frank: Wrong plug can be ruled out. I know I have the correct one, an I have had the cylinder head off and seen from inside that it is correct. Still a question worth asking. I have missed the obvious before. -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.

Les H.: I doubt this one has a nylon ball- or roller cage. Both that I have dismantled had bronze cages, and so have a lot of others that I have seen in bits and pieces. -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.

In general: I have inspected the cylinder bore with the head off, and it looked fine without scores or much visible wear. Can't rule out stuck, worn or broken rings. Fortunately it's only 10 bolts and one exhaust nut in total to remove the cylinder, head and carburettor and have a good look at both piston and rings. Then I can measure (approximately at least) crankshaft and big end play too. I really should do that asap. Then I know and can have peace of mind (and order the reqiured replacement parts). -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.

Fortunately Sachs and the rest of the bike is "very metric". Most bearings are straight from the SKF catalogue, and I have a couple of the almost unobtainable clutch bearing (SKF 393386) only made for Sachs by SKF. Pistons, rings, carb parts etc. etc. are still easy to get, so I should be able to keep this one on the road "for ever". -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.

Btw: the bike is a "Tempo Taifun". I doubt you have ever heard of it, don't think they were ever exported. At least not the military version. It was made by Jonas Øglænd in Sandnes in two civilian versions from 1960 to 1966 and about 630 pieces were made of this particular military model for the Norwegian army between 1964 and 1966. 175 cc, 11 bhp, 115 kg and top speed of 85 - 90 km/h, humming like a big wasp. I bet they would scare the sh*t out of the enemy! Well, enough history class..... -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.

Thanks again, and regards! -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-. Anders F. R.

Hi Anders, Just to be clear about things. I listed the suggestions in descending order of likeliness. That’s why I said the main bearings “were not likely” to be the problem. Frank and I also said it is unlikely to be big end wear, but then you say there IS a chance that both the main bearings and the big end WILL need checking, which is the opposite to what you and ourselves had said earlier. I note you don’t comment on the chance of it being small end wear and this was my second suggestion after the possibility stuck rings. Anyway, you will soon find the problem when the barrel is removed Anders I’m sure. Good luck.

Smallend wear is my vote. The bearing will probably be a needle roller and these can suffer from rust due to condensation, especially during a long lay up.
REgards, Mark

Hi again! -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.

Les H: My English may not be good enough.... What I was trying to say is that when I first take off the cylinder, I can "investigate" both piston, rings, small end, big end AND to a certain degree main bearings. Total main bearing failure should at least be obvious. Hopefully you are all right in that main bearings and big end are not the problem. -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.

Mark M: The small end is a plain bronze bearing on this engine. I have never heard that these are likely to fail, but it may still be possible. -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.

Thanks again for all good help here.Tomorrow I will put my Model G in winter storage, and then the BMW R50. After that I may have time to look at the Sachs engine again. -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.

Regards, Anders F. R.

Hi ANDERS-----------something like this ?? }------ http://www.tempo-online.net/taifun.htm -----------------

I worked in a motorcycle shop in the early 80's and have seen very pitted
needle roller big ends pitted from storage due the acidic nature of the oil used , running the engine not knowing will run out the bearings in a flash , I just cant remeber the make of oil that did it or if this is still a problem with oils now .