K&B .40

All outboard, inboard and aero questions answered here.
ALSO Veco, Torpedo, Fury, & Stallion

Moderator: SteveM

K&B .40

Postby chuckstarck » Tue Oct 04, 2011 3:09 pm

I have three of these, all are Torpedo version, the beginning of time where I come into the picture.

Two are still in excellent running condition but the third just isn't right.
It has virtually no compression. You can start it with a starter but not by hand which is my preference for these engines as they will start in the first if not the second flip after a simple two turn prime and they do it every time for me.

This engine will start and run hard if you keep the rpm up but if you drop to 1/3 throttle, it will start to sag, like either rich or lean, sounds more like lean but that's not the issue. Sometimes you can not get it to fire at all because the compression is nada.

So the choice, simple, put a ring in it, it's 40 years old and deserves a ring. The old one has a .0013 gap, gee that a lot but others have even run well with that gap. Never the less, put a ring in it. The new ring is so tight you can not hardly get just the ring in the cylinder. So I scotch brite the inside to get rid of a glossy black residue, not carbon, looks like the glaze from a fire place on the glass. The ring fits and it doesn't bind and it really looks like this will fix it. Noop, wrong guess. So I put the head in soapy water and spin the crank, no leaks around the head and none at the plug.

When the piston in the downstroke passes the bypass, it really pops which tells me that the ring is sealing 'down' but not up. Go figure, I need it going up.

What's your opinion on the problem? I thought if the ring were not sealing to the piston, it would show in the down stroke as the crank pressurizes as well. Another bad guess. I'm stumped.

:?:
chuckstarck
 
Posts: 7
Joined: Tue Jun 02, 2009 5:33 am
Location: Colorado

Postby Steve J. » Tue Oct 04, 2011 3:14 pm

Cylinder in backwards?
Steve J.
 
Posts: 16
Joined: Mon Sep 26, 2011 2:07 am
Location: Clovis, CA

cylinder

Postby chuckstarck » Tue Oct 04, 2011 4:55 pm

cylinder may be in backwards but that would be from manufacturing back in the 60's if it is. I never removed it from the casting.
chuckstarck
 
Posts: 7
Joined: Tue Jun 02, 2009 5:33 am
Location: Colorado

Postby MECOA » Tue Oct 04, 2011 7:27 pm

The bottom surface of the ring and the bottom surface of the ring groove must be perfect. Clean any varnish.

It sounds like blowby. You must prepare the cylinder surface when you install a new ring. See this even though you didn't score the piston http://www.mecoa.com/faq/piston/scored/scored.htm

The K&B 40 has a Dykes ring which don't feel like they have compression. Read this..
http://www.mecoa.com/faq/abc/abc.htm#ringtype

Check the piston/cylinder to be sure they are correct
http://www.mecoa.com/faq/whichway/piston/piston.htm


The gap can be up to .0025 -- Ring gap rule .003 per inch of bore.
MECOA
Site Admin
 
Posts: 1095
Joined: Mon Jun 30, 2003 9:48 pm

thanks for the response Mecoa

Postby chuckstarck » Wed Oct 05, 2011 3:18 am

Sorry, decimal in wrong place .0130

I cleaned the ring land but I'm going to break the old ring and use it to check that again.

I did use green scotch brite, and it looks just like your picture. I did clean away all the black varnish on the cyl.

The ring clearance visually looks very much the same all the way up and down. Almost completely closed. Light just barely passes through the gap in the new ring.

I understand the Dykes compression. This engine is not like the other two. You can spin the prop with your index finger like the plug is not in the engine. No compression during the up stroke. the down stroke has compression against the crankcase where you hear a good pop and can feel it in the prop when it passes the bypass.

I'm going to clean the ring land with the old ring broken as a tool (carefully).

It may be this black varnish (if it's varnish) along the bottom of the ring land. Do you have a better process to clean the varnish other than using a broken ring?
chuckstarck
 
Posts: 7
Joined: Tue Jun 02, 2009 5:33 am
Location: Colorado

Postby MECOA » Sun Oct 09, 2011 6:20 pm

Actually a broken ring is good cleaning tool.
MECOA
Site Admin
 
Posts: 1095
Joined: Mon Jun 30, 2003 9:48 pm

fixed it

Postby chuckstarck » Wed Oct 12, 2011 5:36 am

Cleaning the ring land with a broken ring was just the ticket. Even with 20 power lenses, I could not see anything there. I cleaned with the old broken ring using each half going in opposite directions. Very very successful. The compression is so high now that without a prop, using the back plate to turn the engine over, almost not possible. Maybe better than new!
Thanks Mecoa for confirming my broken ring option.
chuckstarck
 
Posts: 7
Joined: Tue Jun 02, 2009 5:33 am
Location: Colorado

Postby chiefss » Wed Oct 12, 2011 11:04 am

How do you use the backplate to turn the engine over? I thought the backplate was bolted to the crankcase.
chiefss
 
Posts: 611
Joined: Sun Sep 30, 2007 1:22 pm
Location: Bremerton, WA

turning the engine over with the back plate

Postby chuckstarck » Thu Oct 13, 2011 6:33 am

Actually holding on to the back plate is the best place to hold the engine, then by a simple turn of the wrist, the engine can be 180 degrees turned within a fraction of a second. I have started some engines and held them in my hand, up to a .15 by holding the back plate, yes that is true.

Now for your real question, propeller backplate, silly. lol
chuckstarck
 
Posts: 7
Joined: Tue Jun 02, 2009 5:33 am
Location: Colorado

Postby chiefss » Thu Oct 13, 2011 10:31 am

That is called the prop driver, or drive washer, silly. NOT the prop back plate. LOL. The back plate is the cover on the rear of a front induction engine.

I'm, just so silly. But at least I know what the parts of an engine are called.
chiefss
 
Posts: 611
Joined: Sun Sep 30, 2007 1:22 pm
Location: Bremerton, WA

Postby MECOA » Fri Oct 14, 2011 8:15 am

MECOA
Site Admin
 
Posts: 1095
Joined: Mon Jun 30, 2003 9:48 pm


Return to K&B Mfg. Engine Tech Questions

Who is online

Users browsing this forum: Google [Bot] and 22 guests

cron