357XP advice

[timber tim]

On 11/07/2020 at 12:00, frammo said:

the score under exhaust port wont hurt its out of combustion/pressure stroke.have got many a saw going with worse than that..just ad meteor piston?the one running up to combustion chamber will cause problem if it is deep(bog down under load)if you cant feel it with your nail should be ok....brake hone at top is cheap option for final hone or if money is no object the yellow one.for sake of 20 odd quid and half hrs work i would run that barrel again.hope of help? ps use wd40 for honing

 

Slight catch to my finger nail on the upper score running up to the combustion chamber unfortunately- but from what you say its probably worth honing the cylinder and giving it a go. Have seen the flex hones on you tube and wondered if they were just a gimmick so good to know they work well. Do you think that using a compression gauge once reassembled will show if the score will cause a problem? Or is the only way to fire it up and to see if it bogs down?

[bmp01]

Flexhones are pretty harsh and not what you'd call precision items. Seen them used on 4 stroke engines successfully after some practice but don't think I'd like them 'balls on sticks' running across a port. At least with the brake hone the stones are tall enough to not 'fall' into the port.

Just my 2 pence worth....

 

 

[spudulike]

Interesting on how others work. I measure compression cold and if I then feel it is suspect or feels less than I have measured when cranking, measure again hot so I get a comparison of the drop when hot.

One of the most telling parts of the compression test is the measurement after the first pull, if it comes up high on the first pull, it generally shows an engine in good fettle.

[aspenarb]

There are a few things to consider if second lifeing barrels. Firstly is the piston rings, chrome or Nikasil bores normally run with softer rings, soft bores like iron blocks run with harder rings. Bore finish for obvious reasons will impact on ring life, soft rings designed to run in a chrome bore should not really be used in a honed bore. Less is more if you are poking abrasives up a chrome bore, just saying.

 

Bob

[spudulike]

2 hours ago, frammo said:

 pps what does the comparison between hot and cold tell you about condition of saw

If compression drops significantly when hot, the saw will lack any grunt, torque, mojo.....poor compression hot maybe wear to the piston, ring/s, or bore, it is possible the saw has nipped but the ring is loose enough to seal but is scored......etc

I do tend to use the starter handle to tell what the compression is like and use the gauge if it feels poor. Ergo start mechanisms do mislead at times making a saw feel low compression when it is really OK and some saws often feel low but when measured are fine - just the size of the pulley used.

Many times a saw comes in for a rebuild and a compression reading cold is all you can do as the saw isn't running and it does give you an idea of the state of the saw. and the type of work needed.

A cold compression check does give you an idea of what the engine gets to start it especially on the first pull. I generally use it more if I have a bad starter, saws that feel a bit low after a rebuild and ported kit.....everyone has their own methods and ways of gaining info from kit being repaired or modified.

[bmp01]

6 hours ago, frammo said:

personally i only compression test ported saws to check i havent overdone it..

Ok. Interesting point, what numbers do you use to say you've over done it? 

220psi is ok for a works saw but I've not managed that. ..

Edited July 18, 2020 by bmp01
Typo

[bmp01]

From my limited experience I'd say that's reasonably conservative cylinder pressure.   Looks like you've gone for a small squish to get over the high exhaust port ( "97 degs ex" ---> 166 exhaust duration, big number). You dont get any piston to det band contact with that ? 

 

 

[Joe Newton]

I think my ported 357 was pulling in excess of 200psi cold when Spud did it. That was a reconditioned cylinder from a previous seizure. 

 

That was a few years ago and it's been worked hard ever since. 

[spudulike]

What happened to the OP and his issues??? Any luck sorting the low compression?

[Joe Newton]

16 hours ago, frammo said:

Post a vid running 18” 3/8” through green oak am interested to see it perform ?

Send me a new 3/8 b&c and sprocket and I will...