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compression

Posted by john_evans1 at September 25. 2017

Having finally bought a compression tester to establish why my m50 is so slow up hills I find the readings to be quite good..or better than anticipated.

I get 110psi cold and the same warm..not hot.

Are these figures normal. I would assume so but cannot find reference to baseline figures.

Thanks.

Ps it was so slow up hills yesterday that I was in danger of being overtaken by a fastrack tractor!  I do not like to rev the nuts off it so could have gone faster but it was hard work!

Re: compression

Posted by John Oldridge at September 25. 2017

Hi John,

I could only dream about figures like that, I had a thread running a while ago about the same thing, my psi figures were way below yours, and I can easily kick it  over ( hot or cold). To try and improve the psi reading I even fitted a new head + valves etc, but it didn't improve much. I have to say that my M50 (Slimline 1960) performance seems ok, ie 55-60 ish on the level but I do tend to ring it neck a bit. As its only a 350 with a lightish short stroke I always tend to drop a gear(or two) to maintain momentum on hills......................It is what it is!

​Regards John O

Original thread April 2017

Re: compression

Posted by john_evans1 at September 25. 2017

John. Yes I knew 100psi was a good base but it is a cheap tester hence maybe not that accurate. When I bought the bike I could stand on the kickstart but it is now easier to turn over.

I saw 60 on a downhill straight yesterday but have a feeling the speedo was reading a bit slow. I had a spell where revving the engine hard loosened the tappets but tbis is now resolved. I do not want to risk ut though so am reluctant to rev hard in low gears.

45mph is a nice pace but even then upgrades loose speed and require patience or hard work to regain speed.

I really was hoping that the compression guage would give me reason to lift the head and check it over..but it is not worth doing based on the results.

The readings were at pull throttle.no additional lube to the bore. I then started it up and ran it for 5 mins then retested. Not really up to temp but a fair estimate. Readings were very similar and show no loss after 3 minutes.

Maybe I will have to settle for capn slow but I still feel there is more to come.

Re: compression

Posted by David Cooper at September 25. 2017

I'd suggest a rev counter (so you can see that it's really not revving too hard - they all sound like that) and a pair of ear plugs.  Ear plugs are good for at least +10mph in every gear.

As Jo Craig is supposed to have said: "an engine has no sense or feeling...."

Re: compression

Posted by Dan Field at September 25. 2017

My model 50 is still in boxes and missing a few important parts so I can't comment, but I took my poorly running jubilee out at the weekend and that comfortably managed 45, so I guess your 350 should do a bit better! Have you checked the gearing?

Re: compression

Posted by john_evans1 at September 25. 2017

David

Joe Craig did not pay for his own repairs. Knowing there is a potential issue means I do not push my luck. High revs and a jumped push rod due to loosened adjusters equal a bent pushrods and breakdown on inhospitable moorland with a poor mobile signal.

I do not worry how things sound unless very bad,but I do worry about the effect of vibes at sustained high revs.

 

Dan.

Gearing is standard. It will slog,it will rev but will not maintain pace up hills with my bulk aboard.

Re: compression

Posted by boo_cock at September 25. 2017

I think you may be barking up the wrong tree here. Try checking your ignition timing and points gap. Give it a bit of advance them try a retard and see what happens. Easy if you have manual advance system on a magneto.

Next try feathering the throttle a bit or give it a bit of choke to see how it behaves. Then change the jetting to suit.

Yes, low compression makes it flatter than a fart, but so do a combination of other things too.

Try testing your compression gauge on various other bikes for comparison and get some sort of bench mark.

Re: compression

Posted by John Oldridge at September 26. 2017

Hi John,

Boo-cock? has good  points,....check the timing, etc mine was a little bit retarded, and correcting it improved performance. I achieved a genuine 68 mph on Saturday (Our last Yorks branch ride out) but it was on the A59 coming to Bolton Abbey down hill !  I have a sat-nav on the bike to confirm speeds.(the chrono reads about  8mph fast at 60!)

Regards John O

Re: compression

Posted by robert_tuck at September 26. 2017

Have you checked the valve timing?, not whether the marks line up but with a timing disc , It seems it can be out enough to turn a sloth into a slug.Without substantial modification it will never feel happy trying to keep up with A road and motorway traffic. However it is an ideal mount for club runs round muddy lanes and trips to the shops. I don't have a bike that will do less than 90mph  but none are relaxed when cruising over 60 , its all relative.

Re: compression

Posted by George Phillips at September 26. 2017
You don't say which year your M50 is, John. 110psi is roughly equivalent to a CR of around 7.5:1. The good book (Bacon) shows the a CR ranges over the years to be 7.0:1 ('33 - '39), 7.3:1 ('55 - '58),7.3: ('58 - '63) and 9:1 ('64 to '66). Hope this helps. George

Re: compression

Posted by John Shorter at September 26. 2017

You cannot expect a 350 single to be happy, flogging up hill in top gear, better to change down, and use a few more revs.  that being said, my old BSA B31 would hold 65 m.p.h, on the flat, the equivalent Norton should be capable of, at least, the same.

Re: compression

Posted by christopher_shepperd at September 26. 2017

The smaller engines are happier when they have good RPMs.  Slogging the engine as it sounds like you are will not make it last any longer.  Give 'er some stick and she'll love you for it.

Re: compression

Posted by john_evans1 at September 26. 2017

Lots of response. Thanks you.

It is a 63 model. Valve timing is ok. Ignition timing is fine and has been experimented with.

Plugs are usually dark brown to black but dry. It goes better with an n9ycc than n5.

I do not slog it in top gear. Just commenting that I do not hammer the bike as a matter of course. If I have to then I do but not all the time. The hills I were quite steep.second gear and 25 mph. Throttle just enough to maintain speed.more throttle did nothing and less lost momentum.

Carb settings are standard and the carb fairly new. Choke when riding kills performance so settings are ok. Mpg however is poor. Mid 50's..

I have been riding/building bikes for 43yrs but the lack of reliable performance stumps me..some days it flies..60/70 easy.other days it struggles.

Re: compression

Posted by robert_tuck at September 26. 2017

Sounds a little rich probably on the needle position.

Re: compression

Posted by john_evans1 at September 26. 2017

Yes Robert. My thoughts too, however having tried each nedle position it runs best in position 2..I.e. standard. The top position gives good low down power but goes flat at higher revs.

The lower positions were just flat and hopeless.

I even tried a no 0 needle I happened to have, wow it went well up to 30 then hopeless after that.

Re: compression

Posted by Dan Field at September 26. 2017

Interesting, I know nothing about Amal needles but wonder if a new needle and needle jet would help? Is the cutaway standard?

Re: compression

Posted by john_evans1 at September 26. 2017

Yup..all standard parts in the carb...This is why the bike is such a quandry. It goes ok. Is slow but reliable yet at times goes VERY well for no obvious reason.

I bouught it from a chap in cornwall who had two. He bought this off a friend but decided ge preferred the other m50. Probably because of the erratic performance. Anyway I have a love hate relationship with it so will resolve matters...oh did I mention the fork has started leaking at the bottom?  Great!!

 

Re: compression

Posted by Ian MacDougall at September 26. 2017

Apart from the carburation, ignition & valve timing issues already discussed here are a couple of things that took the edge off my 19S performance in the past:

At one point I thought it would be a good idea to fit a carb bellmouth with gauze to act as a spark arrestor. It took me a while to realise that it also presented a significant resistance to air flow.

At another time the silencer developed a bit of a rattle which I ignored for a while but eventually decided to treat the bike to a new exhaust. This gave a noticeable increase in performance, I can only assume that the rattle was due to a loose baffle which was restricting gas flow.

Ian McD

Re: compression

Posted by john_evans1 at September 26. 2017

Interesting Ian. My silencer is fairly new.No loose baffle but fruity! The Down pipe does loosen a little at the port but there is no soot etc evident.

the carb has no obstruction.

Re: compression

Posted by Barry Carson at September 27. 2017

are the chain/sprockets in good condition

are there any brakes sticking

tappets ok

check the chainguard see if its sitting on the chain when you get on the bike

is the fork oil leaking from the top nut and running down dripping off the bottom

 

Barry

 

 

Re: compression

Posted by robert_tuck at September 27. 2017

Most of my enjoyment in running old bikes stem from the oppertunity to tinker and "improve" things .

Re: compression

Posted by George Phillips at September 27. 2017
I think it's called "bonding", Robert.

Re: compression

Posted by ian_soady at September 27. 2017

I must admit all the 350s I've had have felt gutless. I had a B31 in the 70s that wouldn't do more than 60 realistically; more recently a Velo Viper which went well but only if it was wound up till the valves nearly bounced.

They all suffer from having to lug about a heavy frame etc usually well capable of handling their 500cc stablemates.

I much prefer the lazier power delivery of the bigger engines.

Re: compression

Posted by robert_tuck at September 27. 2017

I got to "test ride" a Yamaha MT09,  the  instant power from any revs or speed  is enough to get the front wheel up so fast that you could ride it like a unicycle  (well  --someone could!) , bloody terrifying , and impossible down some muddy lane without electronic gismos to manage it, bit like a jet fighter that is uncontrolable without a computer to help. Give me a 350 Norton anytime, or a test ride in a Supermarine Spitfire!.

Re: compression

Posted by john_evans1 at September 28. 2017

I agree about the weight of the machine..plus my bulk but seriously doubt the bhp figures suggested for the engine.

I also understand that an old 350 does not compare with a modern superbike and am familiar with both types having owned bikes as diverse as a zzr1100 and 1920'svflat tanker.

The Norton is not much better than the oldie.

I used to enjoy tinkering but the older I get the more I prefer to simply ride. The suggestion of bonding suggests unreliability to me,not fun.

Each to their own of course but riding is more important to me than working on it in the shed.

Re: compression

Posted by tony_harris at October 02. 2017

My 59 NH 350 Ariel would do about 75mph and hold 60mph loaded with luggage two up. To be fare though it would struggle on hills so I just changed down.

Check other things as suggested.

Re: compression

Posted by john_evans1 at October 04. 2017

I went for a ride today and drove the bike harder.

Topping up with v power I travelled at 50 ish for 20 ml.

Lots of fuel was guzzled and once home the plug was checked. Dark brown so not bad.

I then checked compression with a hot motor. Again 110psi..no change.

Leaving the guage connected for five minutes no leakage was detected.

The bike still seems slow in spite of these readings.

I tried posting an image of the guage/reading but cannot seem to achieve it...message says file too big.

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