Piston rings muddled up

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

Hacksaw

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

Emgee

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 ..

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

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

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.

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

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

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.

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

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

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

Aghh still wont go

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...

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...

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 .

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

Lack of ignition then?

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.

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.