Compression test

[07_Z570]

School... like a month ago. Nascar Technical Institute, Mooresville, NC 28117 or 28115 I dunno which zip code they have..

[Danzig]

Have you finished up your schooling?

[07_Z570]

The Basic engines.... Yea.. Been through Brakes a little while ago. just went through Electronics.

[Danzig]

Where did you learn about the rings spinning on the piston? How was it presented to you in class?

[Liquifire 4/6]

Nick, the four stroke engines you've been learning about in school are considerably different than a two stroke mill. I know nothing about automotive engines, but I assume they have piston/rings similar in design to the lawn mower and tiller engines I've worked with. On the small four strokes I'm familiar with, the rings should be free to rotate on the piston. But this is an no no with a 2 stroke motor as the two strokes have many ports within the cylinders and narrow bridges between the ports that a ring can snag on if the gap happens to slide past it. That's why 2 stroke rings are held in place on with a ring retainer pin located in a specific position to keep the ring gap from straying into an undesirable area. I do stagger the ring end gaps when I assemble a 4 stroke engine, but being that I've yet to see a glass cylinder, I've no idea how the rings behave when it's running.

[07_Z570]

If the engine was rebuilt and shows such awful compression on one side it would appear they just threw in a set of new rings and never checked the tolerances of the bore. If you can get the heads off try micing the bores and comparing the values to the specs for your machine.. If I remember correctly a sticking ring will also show an increase in compression with an oil test. -Mike

Now, like you said Pete, 2 strokes use a Piston ring lock. Whats he(mike) talking about?

Yea, we've got a Glass Motor thing.. Runs on alcohol... they didnt Show us the Rings rotating with that.. Just how Spark Advanced or retard looks. Position of the pistion when the Combustion Occurs.. Pretty Neat.

Well Its the Same idea right? He does need a set of Rings in that motor right?

[Danzig]

Nick-

Learn from this post and I would like to know what your instructor is teaching also or if you assumed, I am only trying to help you in your future because I would be much better off today if I would have listened.
I was once a engine builder on a Winston Cup team in 1988-1989 fresh out of high school, probably close to your age. I worked in Kannapolis, North Carolina and lived in Concord, North Carolina. The team I worked for was the Sunoco Ultra Racing Team, car #98. Brad Noffsinger was the rookie driver. The building I worked at was licensed under Curb Motorsports. Or if you have or havent heard of Curb Record Industry (as in music). I was an apprentice in the engine building department for this team. I have done it all when it comes to these engines which were 357 Chevy's running Victor Junior Intakes and Holley carbs. Not sure about todays rule changes etc. I left there due to my own stupidity, girlfriend and being homesick, moving to North Carolina in June of 1988 after graduating from high school in May of 1988. I have also been involved as an active automechanic ever since and still tinker a bit these days too. My father and brother have both also worked at GM dealerships and we have also had an auto repair shop that we had run.


Back to North Carolina before I end this drama and my proof of my back round. If you do a google search and type in "Leading Edge Race Cars". There should be a telephone number listed for this business. The owners name is Pat Beattie. He has 2 sons Kyle and Eric. Both racing stock cars these days and I used to be their diaper changer on Sundays when Pat was at the race track or on the road. Pat moved to North Carolina with his wife Glenn from my home town in Illinois to go to the big show, Winston Cup. Well, his big show dream came true when he became the car hauler or truck driver for the late Alan Kulwicki and pit crew member as the windshield washer. Pat called me back home in Illinois and said he had a job for me. So, I packed bags and moved to North Carolina and the rest is history. Leading Edge race cars is a company that makes or has made the roll cages for the Craftmans series truck circuit. This was what was going on in 1997 when I was there last. Give Pat a call and ask about me. My knickname was Sasquatch (big foot)

Now, piston rings on 4 stroke engines cannot spin on the piston. Each ring is put on the piston with the ring gap 90 degrees the opposite of the other ring. If these rings were to spin eventually all the ring gaps would line up and blow compression right on by the piston, thus ending result misfire and oil being blown out the valve cover, etc.

Honing is done for: to collect oil on the cylinder wall suface and to aid as in a scuff in for the rings to seat and to clean up any surface imperfections left behind from old rings if the engine does not require a bore job.

Boring will be needed: when excessive cylinder skirt wear is found by using a dial bore gauge. Skirt wear is at the bottom of the cylinder wear the piston does not run and at the very top of the cylinder. If an engine does not get bored out and proper rings and proper pistons do not get installed, piston slap will ocurr resembling a connection rod knock. Some people mistake piston slap for rod bearings being bad.

Good Luck with your dreams too. It sounds like you have a bright future going to this type of tech school.

[michwil4]

Hey Paul,

Looks like you have quite the resume. I wished I could have tapped into some of your knowledge when I raced the local dirt tracks a few years ago. I raced Super Stocks for 8 years in northern WI and MN. Racing ended up taking too much money, time, and wives....well looking back, it wasn't all bad...heh,heh.

I bore-scoped that low cylinder last night. I found metal transfer and what looked like pitting on the cyl wall. I'll pull it apart saturday night after I come down from my tree stand...Opening day of WI deer season!

Would you be more inclined to bore a bad cylider or replace it?

mike

[07_Z570]

Well, Sounds like you Sure Know whats Going on!

This is How I Put it, Everything I've Learned working with my grandfather/Uncle in the Garage. I put it all Behind me when i walk into that school. and Whatever they Tell Me, Thats the Way it Must be. However, Every Instructor will Tell you something Diffrent. This same Instructor tells us to Use HOT Soapy water to rinse the Block after a Bore/Hone Job. Because the Hot water will Dry Faster, so you can apply oil. A few days later we had a Subtitute Instructor, and we went over everything with him, he asked what we rinse the block with after Boring and honing, I said, Hot Soapy Water. and every one agreed. Except the Instructor. He said, NO Never Use hot soapy water, Use Cold soapy water. He kinda had an attitude about it. So I proceded to tell him what the other instructor told us and why, and he said he was wrong.

Kinda hard to Learn when Every Instructor has their Own ways. Because the Tests only Have One answer for One way.

I understand the Whole end gaps lining up thing. but Supposedly if they didnt rotate with the hone. the hone would wear rapidly.
I Believe I do remember the Piston Ring End locks on a 2 stroke. Chevrolet/Gm (what we use in the school for teaching aids) Dont have the Ring end lock.

[Danzig]

Hey Paul,

Looks like you have quite the resume. I wished I could have tapped into some of your knowledge when I raced the local dirt tracks a few years ago. I raced Super Stocks for 8 years in northern WI and MN. Racing ended up taking too much money, time, and wives....well looking back, it wasn't all bad...heh,heh.

I bore-scoped that low cylinder last night. I found metal transfer and what looked like pitting on the cyl wall. I'll pull it apart saturday night after I come down from my tree stand...Opening day of WI deer season!

Would you be more inclined to bore a bad cylider or replace it?

mike

Mitch-

Would I replace a cylinder or hone it? Well, you came to right forum for the answers, but snowmobile engines are nothing like the automotive field but also similiar too. I just went through a motor back in August and was unsure about the the cylinders I had for my 80 L-fire. I posted pictures on here of the cylinders and pistons. I do know you dont hone the chrome lined cylinders, you can clean them with muriatic acid which I have done. All I did in the end was replace the rings on the engine and put it back together. I am no tech expert on this forum by any such means. I am learning each day and trying not to lead people with bad or un-factual info.

[JoeRainville]

Hey Guys,

Paul, well stated info on 4-cycle engines. I concure with rings not spinning around the piston, but there might be slight movement due to the change in direction of piston travel.

Now, about chrome bores: Again, you guys were right, all Kawi motors came with chome bores "to the best of my knowledge." However, it is common to find a set that were steel sleeved as a repair. Chrome bores can be honed LIGHTLY to removed scuffs and any aluminum crud.

If you have a burn down, HCL or "Muratic" (sp) acid can be used to dissolve any aluminum stuck to the chrome bore. When you hone, use the finest stones you have with lots of oil. Most any motor oil will work, heck I use 10W30 myself, with a cheap Craftsman hone. Go slow, and you can get a nice light cross hatch. Do not go crazy, as the chrome, although hard, is only a few thousandths thick.

If the chrome is worn through, pealing or badly pitted, you will need to get it nickasiled. They do not re-chrome jugs since nickasil is harder, and wears much better. That is was you get if you send a jug out to "US CHROME". Nickasil is short for Nickel - Chromium - Silicon, (I think).

HOWEVER, you do not use the same rings on a nick'ed jug that you would for chrome. Chrome bores gets iron rings. Iron/steel or Nickasil bores get chrome rings. Luckily, WISCO offers a ring choice for Kawi 440cc motors, and still offers an overbore option if you have a set of sleeved jugs that need overbore.

I hope this helps,
-Joe Rainville


B)

[Maj_hazard]

If the engine was rebuilt and shows such awful compression on one side it would appear they just threw in a set of new rings and never checked the tolerances of the bore. If you can get the heads off try micing the bores and comparing the values to the specs for your machine.. If I remember correctly a sticking ring will also show an increase in compression with an oil test. -Mike

Now, like you said Pete, 2 strokes use a Piston ring lock. Whats he(mike) talking about?

Yea, we've got a Glass Motor thing.. Runs on alcohol... they didnt Show us the Rings rotating with that.. Just how Spark Advanced or retard looks. Position of the pistion when the Combustion Occurs.. Pretty Neat.

Well Its the Same idea right? He does need a set of Rings in that motor right?

The ring moves in and out of the grove within the piston (not rotate) as it adjusts to minor changes in the bores diameter. If the ring or the grove it sits within gets carboned up the small in and out movements become lazy or the ring may outright stick and compression can suffer. The point I was trying to make was a wet oil compression test will indicate a poor seal between ring and bore but does not necessarly mean the rings and bore are out of spec.

I hope I'm a little clearer

Cheers

Mike

[HoosierDeereMan]

Another thing that my be going on here is that there is a broken ring. It gets tough sometimes trying to compress the ring in the groove, line up the locating pins with the piston ring and start the piston into the bottom of the cylinder all at the same time. It is a possibility that a ring may have been broken during assembly. The only way you are going to know is to tear this cylinder apart.

[michwil4]

Thanks everyone...I'lllet you know what I find on monday

mike