Piston rings muddled up

[HacksawParticipant @hacksaw]

I'm doing up a Suffolk mower remember? Well the engine wouldn't go , so i swapped it for another i had , and the mower works. But i want the original engine back on it really..

Been tearing down the original engine , to find out what's wrong with it ,and the inlet valve was rusty .I guess the valve was open and then moisture  got to it .That's now sorted . But , i've got the piston rings off too and without me glasses on they looked the same so i tossed them into the box of parts…

With me glasses on they're different ! Any idea what is top ring and bottom ring ? And orientation? 3rd ring i didn't remove is an oil control one . 'Scuse rubbish drawing , here's the sections . Ring 1 looks a type of ridge dodger top ring

 

?

Edited By Hacksaw on 03/06/2017 21:56:09

[HacksawParticipant @hacksaw]

[EmgeeParticipant @emgee]

Hacksaw

The groove for ring 2 will have a shoulder on the inside to suit the step in the ring.

Emgee

[HacksawParticipant @hacksaw]

No step. And i cleaned the crud out so there's no tell tale of carbon.. There is no ridge on the bore, does it really matter where they go ? It'd only a 1 hp or so ,mower engine ..

[Adrian GilesParticipant @adriangiles39248]

Ring 1 is the top ring , therefore ring2 is the middle ring

[HacksawParticipant @hacksaw]

Ok , but what way up ? Ring one as a ridge dodger?

[not done it yetParticipant @notdoneityet]

doing up a Suffolk mower remember?

Nope!

Not replacing the rings with new? What is the ring gap in an unworn part of the bore? Can you see a line in the ring groove to determine where the inside stepped ring fits? The more worn (on thickness) is likely the top ring.

There won't be a ridge dodger if original, so that step is likely bottom side of second ring. You may need a ridge dodger if the bore is worn and you fit new rings.

Are they square or tapered rings (if not appreciably worn)?

You might need a magnifier as well as your reading specs. If there is metal displaced on the outer edge of the ring (sharp edge) it will be the bottom of the top ring.

[HacksawParticipant @hacksaw]

Square rings . No ridge at all ,low mileage..The second ring groove is slightly chamfered at the top ,under an eyeglass…

[Neil LickfoldParticipant @neillickfold44316]

It looks to me ring 1 is correct and the second ring is upside down. Not sure on your'e exact engine, but a lot of older engines that were one piece barrels, used a ring design like that on the top ring. Most likely due to the limit of blind honing a cylinder back in the day. The gap at the back of the second ring is for residual pressure to push against the ring to make it seal. The ring gap will be in the 0.2 to 0.25mm range, 0.008 to 0.010 thou, with inch feeler gauges. They can still work even at a smaller gap of 0.006 inches , if teh ring gap is too small, it wears the top of the bore prematurely.

Neil

[I.M. OUTAHEREParticipant @i-m-outahere]

Ring 2 is the top ring and the groove faces the top of the piston .

Ring 1 is the second ring and the groove faces the oil ring

Ian.

[Vincent O BrienParticipant @vincentobrien84126]

Hi Hacksaw I have a complete piston from one of these and from checking

Ring 2 is at top with the step at top

Ring 1 is at the bottom with the step at the crank side

Vince

[HacksawParticipant @hacksaw]

Thanks chaps , I'll go with that then..

[not done it yetParticipant @notdoneityet]

Compression rings have other duties than simply confining gases within the combustion chamber. They also help regulate the amountvof oil passing upwards in a four stroke engine and transfer heat from the piston to the cylinder walls. This latter duty indicates that the piston is rsther hotter than the cylinder walls. Therefore the rings will expand rather more than the cylinder. Interference, rather than sliding fit can lead to engine seizure, not just excessive wear.

Ahh, I see it is fairly modern engine design, a separate head – not a blind cylinder. Look at the B&S engine ring types used. That may be useful.

Or this may be more useful:

http://www.oldlawnmowerclub.co.uk/forum/suffolk-75g14-piston-rings-non-original

[HacksawParticipant @hacksaw]

Aghh still wont go

[MuzzerParticipant @muzzer]

Have you got a fat blue spark if you remove the plug and crank the engine? That always seemed to be the main weakness of these engines. If it's been sitting outside for years, the HT coil is likely to have moisture inside. You also need a decent condensor for the ignition to work properly.

This assumes the carb is getting mixture into the cylinder and the plug is not fouled / flooded.

I used to do these up as a source of income many years ago…

[HacksawParticipant @hacksaw]

Yes yes yes ,everything honky dory with it . Just wont run ! These things even clapped out will still try and run . Not this one though !

I fart about with them Suffolks too !

Here's my John Player Suffolk ….and my Marlboro Honda Suffolk conversion….midlife crisis maybe? Don't tell anyone…

[I.M. OUTAHEREParticipant @i-m-outahere]

Could also be a crook plug , blocked carby or stale fuel .

I usually head for the plug first to see if it is wet or dry looking , if it is dry the carby gets a visit and if it looks wet i check over the ignition system .

[HacksawParticipant @hacksaw]

It runs! Swapped the stator and flywheel . And makes a terrible metallic rattle I think I'll paint the other engine and leave the nasty one under the bench. No one will know it's not the original

[KWILParticipant @kwil]

Lack of ignition then?

[Clive FosterParticipant @clivefoster55965]

Always felt those small Suffolk engines were about best of breed for mower duties. Seemed to go on pretty much for ever (OK 20+ years) if you changed the rings every couple or three years. Don't recall seeing any significant bore wear on any I went inside but newest one was probably 1970 ish build. Guy up t'mower shop reckoned the rings were made so as to wear rather than the bore.

Usually changed crank oil seal, points and condenser maybe every 6 years. Always did all three together when one needed attention. Valves probably due for a grind by then as well so scrape out the carbon too for proper bithday time. Broke all the rules and changed the oil every year which may have helped.

Clive.

[HacksawParticipant @hacksaw]

I guess it wasn't firing the plug under combustion conditions, sparked the plug out of the head though. The Dennis Bros. of Guildford 1960 mower restoration starts soon , that's got a big magneto , with fat juicy sparks already.. . Roller seat is absent , I'll make one from a gas cylinder.

[Howard LewisParticipant @howardlewis46836]

Piston Compression rings have internal chamfers or steps (usually at the top) to ensure that they twist and present a sharp edge to aid scraping oil off the bore, when descending on the power stroke.

Some rings are tapered to produce the same effect. Compression rings have a lot to do with oil control, and control of blowby.

The contact markings on the rings ought to indicate which way up they were fitted, unless so worn that they have already made full face contact., in which case maybe they should be replaced.

Many compression rings are gas backed, i.e. cylinder pressure assists the inbuilt ring load in producing the required wall contact pressure. Off load, this results in reduced friction, and fuel consumption.

For this to work well the surface finish of the side of the ring and its groove become important, as well the vertical clearance in the groove.

Nor are Compression Rings, necessarily round. They can have positive or negative ovality, depending upon the plane of the ovality, relative to the gap.

Ideally, the ring gap should be the least that prevents the ends butting together when the engine is under full load and hot. If the ring ends butt, breakage and damage to bore and piston is likely.

The usual gap is of the order of 0.001" – 0.002" per inch of bore diameter.

A Top ring with an external step at the top is only used as a "ridge dodger" to avoid contact with the unworn area at the top of a worn bore.

Oil control is a combination of wall pressure, liner cross hatch pattern and surface finish.

Many years ago engines had to be run in gently to wear off the peaks of the marks left by the boring bar.

Modern engines have the bore finished by honing, followed by a plateau hone.

Plateau honing does that before the engine is assembled, and leaves some of the helical grooves produced by the first hone, which act as oil reservoirs to prevent seizure. The correct combination of cross hatch angle and wall pressure will produce good oil control without the risk of scuffing or seizure. Get the combination wrong, and you will have problems!

The Suffolk Punch engines have no valve clearance adjusters.  Like the old Ford E93A side valves, the clearance is set by assembling and measuring the clearance (if any after reseating the valves)  and then grinding the end of the valve stem to obtain the specified clearance. For those who got it wrong with the Ford, there were service tools which elongated the valve stem by pressing a radiused  groove into it!"

Howard

Edited By Howard Lewis on 04/06/2017 21:08:43

[HacksawParticipant @hacksaw]

Many years ago , a boy had a go kart. It was his best toy . During the summer holidays after endless hours driving this thing up and down their remote lane , a piston ring let go and the engine no longer ran…

Really the 2 stroke engine had had it….A rebore was £17 including a new piston,and he didn't even have 50p in his shorts.. What to do? he thought . Something springy… He rummaged in dads garage, found some side cutters and snipped a spoke off a bike wheel, bent it round the piston and hammered it flat enough to fit in the pistons groove,little bit of filing and the piston was refitted , head on , plug connected..Did it work? Yes,it did !!! Long enough for me to save up 17 quid!

Some years later , on the same kart , I went tearing round a bend in the road, flat out , and crashed into the village copper on his motorbike coming the other way, knocking him off … Try doing that these days!.

[Nick_GParticipant @nick_g]

… Try doing that these days!.

.

It would be 50 bullets and a bystander member of the public accounting for one of them.

Nick

[HacksawParticipant @hacksaw]

I didn't mean it to come across like that, sorry.

[Author]

Posts