Breaking in engines on LPG 3

[cheguitarra]

Please forgive me if this is an unchallenging question, but i'm an electrical engineer looking to give my automotive pride and joy a new berth of life!

I have converted my Suzuki Sierra (known as a Samurai in other parts of the world) to run straight LPG and all has been running swimmingly for the last two years. But alas, time has come to rebuild.

On the side I have a G16A (1600cc 8v engine) I plan to rebuild to stock specs (unless specified otherwise), i'm running an Impco CA100 propane mixer, and the dizzy timing has been re-curved to suit the LPG fuel. I'm concerned that I may have issues seating in the rings of a freshly rebuilt motor on LPG, being a dry fuel i'm not sure if I need to take precautions during the breaking in process, or if I should avoid an LPG break in all together.

Whilst i'm aware of the general breaking in process, LPG information is extremely limited and any tips that can be forwarded my way would be greatly appreciated. I love my ride and it's my first and only car.

Thanks in advance for any pointers

 

[patprimmer]

If practical, I would raise the compression, probably a full ratio when rebuilding.

So long as the bores are straight with good finish and the ring end gap and piston to bore clearances are OK, follow the normal ring bedding procedure then go for it.

A dry fuel actually helps avoid the bores being washed down with fuel.

Regards
Pat
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[cheguitarra]

I believe with the machining involved the compression ratio will automatically raise from 9.5 to 9.8:1... but that's just the maths i've done. I will investigate what pistons can give me an even higher CR.

My main concern is my want to use chrome piston rings for longevity, but in regards to my rebuilder motor i've heard disputable chinese whispers of trying to seat such rings on LPG, moreso they don't seat and will just glaze the bore. Can this be confirmed or dismissed?

My thoughts are that the 'chinese whispers' engines are just internet ramble, were not broken in or loaded correctly in it's infancy, or something to this degree, but I don't want to ignore without investigating.

Thanks for your fast reply Patprimmer

 

[patprimmer]

If you are buying pistons I would aim for around 11:1 if available and economical.

Chrome rings take a lot longer to bed than iron rings.

I preffer iron rings for good seal and they are kind to the bores. Better to only wear rings than to wear bore.

Warm up and run at fast idle for 30 min to bed the cam and followers, then very short pulls at full load with a good cool down fast idle no load for a minute or two, then a slightly longer pull etc etc until the pulls are up around 10 seconds and red line rpm.

Don't be afraid to apply full load, just don't do it for very long initially as you don't want localised heating on the tight spots to score the bore, but you do want load on the rings to bed them hard against the bore.

Regards
Pat
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[belgian1776]

Back in the 80s when I worked at a local machine shop we built quite a few small and big block chevrolet engines that were propane only motors. We would run 11 to 1 compression in the small blocks and try to end up with 10.3 or so in the big blocks..
We also drilled a very small notch in the top of the guide on the exhaust side to make sure the exhaust valve was well lubricated.
We used chrome rings many times also.. Heat is what seats the rings. Like Pat, I am convinced that the dry fuel actually helped the rings seat. We never had any trouble with the rings on a propane motor. I don't know if this is any help but I thought I would kick my 2 cents in..

 

[Tmoose]

Lots of reputable sources attribute the accelerated "engine wear" during warm up to corrosion based wear from the condensation of combustion products onto the relatively cool cylinder walls. Once the cylinder warms above a certain temp, cylinder wear slows WAY down. Some say it practically ceases. Chrome faced rings are themselves highly resistant to the corrosion effects, with the end result that they can "wear" cylinders less than iron rings.

Most of the faced rings are very resistant to scuffing wear also. Probably more than cast iron, despite iron's graphite content. The carbon in the high strength irons (a good idea for top rings in tough applications) is more likely nodular form than a slippery flake graphite form, anyhow.

I think I'd focus my efforts to reduce cylinder wear would be focused on cleaning before assembly and assuring ingested air cleanliness, not ring material.

Some ring manufacturers maintain "no synthetic oil" for ring break in, at least with conventional cylinder finishing techniques.

 

[catserveng]

This is from my way back machine, I think you may be able to find the entire article on Impco's website somewhere, I had it in an old document,

"Impco wrote:
Excessive oil consumption is indicated by soot on the spark plugs and black smoke from the exhaust pipe under heavy load. Contrary to general belief, rich propane mixtures do not cause black exhaust smoke. A mixture rich enough to produce smoke will not burn in a combustion chamber. Blue smoke is oil vapor; black smoke is burned oil. Causes include worn intake valve guides and seals, poorly seated piston rings or broken rings and ring lands.

Because propane is introduced into the combustion chamber as a dry gas, lubrication on the cylinder walls does not wash away, and the cylinder bore wear is virtually eliminated. In spite of this obvious advantage, propane's gaseous nature is the very reason that rings do not seat in a propane fueled engine. The result is excessive oil consumption.

Oil consumption can be completely eliminated if handled correctly. We advocate the use of either a moly-filled or cast iron top ring. Chrome rings should not be used to unless the engine is first run on gasoline to seat the rings, then converted to propane. Otherwise, the surface of the chrome ring is so hard that it won't seat. A three-piece oil ring with chrome-plated steel rails is preferred for gaseous fuels. It has the ability to scrape oil better than a one-piece ring, and the steel rails conform better to the cylinder walls.

To seat the rings in new or rebored cylinders, a light mixture of Bon Ami and oil is used to "lap in" the rings. Mix two or three tablespoons of Bon Ami with two or three ounces of 10-weight oil to form an abrasive oil. While the engine is on the stand, paint the walls of the cylinders (pistons at bottom dead center) with the solution. Then rotate the engine about 50 turns. Leave the solution on the cylinders -- it will dissipate. A CK10 Sunnan power hone may be used to remove the last 0.003-inch, with a 280 grit stone. When the engine is fired up, the rings will seat instantly.

Evidence of even contact entirely around the ring diameter may be seen by noting the linear (up and down) polish marks over the cross hatch pattern left by the hone. Cylinders should be prepared similar to a go gasoline ring job.

A frequent difficulty is installation of piston rings without sufficient butt clearance (gap). Rings should be inserted in cylinders and checked for specific before being installed on the pistons."

The original bulletin was from the early 80's, sorry I don't have a complete copy.

Hope that helps,

Mike L.

 

[belgian1776]

We never used the "lap in" proceedure that Impco is suggesting. On the engines that we assembled and dyno'ed we would start engine and immediantly put under a light load to get temp up. Then after cam break in proceedure we would do several full load runs, shut engine off then deliver to customer. Never did have any comebacks.
I also dismantled a number of small block engines that had been run on propane exclusively with chrome rings. These engines ALL had severe cylinder and guide wear. Usually the seats were so beat into the head it was more cost effective to replace the heads. The blocks would usually clean up with a .060 rebore but not always. These were all engines that farmers ran in their pickups and were high mileage for that time period, 150,000 miles plus.

 

[catserveng]

I had this in a folder full of Impco documents, it was part of a larger article that is long since gone. I think it had to do with engines being rebuilt for the LA Times distribution trucks in the late 70's.

The guy who was our Impco rep in the 80's had a ton of great info he shared regularly, but since most of we dealt with was industrial engines I didn't keep all of it.

We used to use Bon Ami to clean up cylinders and reseat rings on older diesel engines, had a published procedure for "dusting" and a CAT part number for the Bon Ami.

This old procedure probably had a lot to do with the engine rating and service it was applied to, and it's fairly old, but thought the group might find it interesting.

Mike L.

 

[FeX32]

Some engines are designed purposefully to burn a slight amount of oil for engine longevity.

Also,

Once the cylinder warms above a certain temp, cylinder wear slows WAY down. Some say it practically ceases.

Is this not why we should warm our engines up for a small amount of time before driving off?


Fe

 

[cheguitarra]

Thanks for all the great replies... I am a bit more confident in the project than I was this time yesterday. I'll have to find some of that Bon Ami stuff, i've never seen it here in Australia.


A couple more quick Q's - chrome rings vs cast iron rings... how much faster will cast iron rings wear in comparison to their chrome counterparts?

Also, if I bump up the compression a whole ratio, is that going to substantially affect my initial and all out timing? My dizzy is curved for 14º inital and 28º open.

 

[patprimmer]

Compression and timing depends a lot on several factors like quench between the chamber and piston top and resultant turbulence, bore size, position of plug in the head, coolant temperature intake air temperature, intake valve closing point and amount of exhaust scavenging at overlap so no real hard and fast rules can be made.

What engine is it and how much attention to detail are you prepared to do for minor gains in power and fuel efficiency.

Many of the traditional extra wear with dry fuel issues where more to do with it being unleaded rather than dry. If you run an engine designed for unleaded fuel on gas, it should have exceptional engine life. Taxi cabs for instance run almost exclusively on LPG in Aus.

Ring wear, bore wear and oil consumption past the rings is very dependent on the cross hatch angle and depth and on the final bore finish.

It also depends on piston to bore clearance, rpm turned, oil grade and oil and bore temperatures.

Bon Ami was a competitor to Ajax powder in Aus in the 60s and 70s at least. I would NOT put it in my engine. Proper honing techniques make it redundant and even detrimental.



Regards
Pat
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[Tmoose]

catserv provided Impco info that listed a series of procedures that involved BonAmi. Then at the end of that paragraph IMPCO said " A CK10 Sunnan power hone may be used to remove the last 0.003-inch, with a 280 grit stone. When the engine is fired up, the rings will seat instantly."

Those honing instructions were pretty much the standard cylinder finishing procedure used by decent quality engine shops, at least throughout the 70s and 80s.

My money remains on good cleaning after a controlled finish is created on a round, straight cylnder. I'll let others force their engines to ingest clouds of pulverized sodium carbonate, calcium carbonate and feldspar.

 

[cheguitarra]

Engine Specs as far as I know them


G16A (8 valve SOHC), 4 cylinder, circa 1992.
Bore 75.0mm (2.95 in)
Stroke 90.0mm (3.54 in)
Piston Displacment 1590cm (1590cc, 97.0 cu.in)
Compression ratio 8.9 : 1

I just realised I got the compression wrong... I thought it was 9.5:1... turns out that's the G16B (the superseding engine model).


I'm not looking for maximum horsepower with my rebuild, i've got the wrong car if I want to go fast - basically looking to stay stock as possible with a few tweaks to optimise for LPG fuel. Long term reliability and economy are my primary objectives.

 

[IceStationZebra]

I formerly worked as an engineer for a forklift OEM. We did not worry about piston rings, we used whatever the engine supplier normally used. (GM, Mazda, etc.) The main issue was valve seats - we upgraded to inconel valves and valve rotators if at all possible.

ISZ

 

[patprimmer]

Raising the compression on that to as much as 11:1 will give good increase to power and economy. It may reduce engine life, but not likely to any significant degree.

At what cot the extra mpg is cost effective is another story which you need to do some homework to decide.

I don't have data for typical mpg increase per unit of CR increase, but maybe someone else will chip in.

At a wild guess I would say, maybe 10% increase in mpg going from 8.5 to 11:1

How long has the first engine lasted? How long will the rest of the car last?

Regards
Pat
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[dicer]

I think you should read what Patprimmer says.
#1, DO NOT USE AN ABRASIVE, unless you plan to remove it all after use, do not add it and run the engine forever on it.
So old radial aircraft cylinders and rings are lapped, but the lapping compound is not left on the components.

#2 Surface finish is the proper technique, for your engine.

#3 Propane has a high octane so yes raise the compression ratio
to what Pat said.

 

[Tmoose]

Hastings (a moderately well know US piston ring manufacturer) has this to say -

http://www.hastingsmfg.com/ServiceTips/gas_vs_gaseous_fuels_oil_economy.htm

 

[cheguitarra]

OK, so my concerns are as follows - Impco wrote their reference guide 30-ish years ago when most blocks were cast iron lugs running leaded fuel. Compared to this, my motor was an advanced unit for 1990 - all alloy, Japanese build quality, and designed from the get go to run unleaded petrol, so in theory it's a perfect candidate for LPG. But mis-seated rings seem to be a common point of concern.

I have to ask how modern cars can run on LPG straight from the factory without a hint of fuss (like my dad's 2010 Ford Falcon ute, and every taxi out there)? How can I find out their secrets?

 

[LionelHutz]

Pat basically already mentioned it. The typical break-in procedure is something like this. Run it at a varying 2000-2500rpm for 30 minutes if you need to break in a flat tappet cam. Then, run 5 or 6 medium throttle accelerations up to around 1/2 redline. Finally, run 2 or 3 hard accelerations up close to redline. After, change the oil and drive it like you stole it.

Make sure the cylinders are properly machined (honed) as per the ring manufacturer's specifications and I personally wouldn't bother with any special harder than normal ring material.

I also would personally would run a full synthetic oil unless it has a flat tappet cam where it either needs an additive or typically a non-synthetic oil with higher levels of wear additive.