Compression! Or lack therof......

**Cribbs74** Mon Mar 19, 2012 9:16 am

I bought a .020 cylinder set off of Bernie a while back and I installed it on Indra's TD .020. I noticed the compression was poor but, I figured it would tighten up one broke in. So I ran a couple tanks through it with a rich setting and then on the third tank I let er rip! Spools up fine runs real steady except the compression is still lacking. I mean it's lacking a lot. No pop just kind of turns over with a very slight bit of resistance. My other .020 has a good pop to it and the propeller spins around and whacks my finger when hand spun.

I know cylinders should be matched with good fitting piston's but, I figured a NIP one would have good enough compression from the get go.

Any ideas, it runs ok but, when it's cooled down zero compression.

I lapped the head and it has a new gasket installed.

EXModelEngines Mon Mar 19, 2012 9:33 am

A couple of thoughts:

Could be the glow head gasket (even though you changed it for a new one, try another) or the fit between the head/gasket/cylinder. Check underneath the gasket where it sits on the cylinder. Many of the new old stock ones had issues with old oil hardening from sitting over the years. I would clean the seat well and make sure it is a tight, flat fit. Also, try taking another glow head to see if that makes a difference.

The only other thing might be the cylinder itself, but that wouldn't be too likely since you mentioned it is brand new.

Matt

SuperDave Mon Mar 19, 2012 9:43 am

Ron:

As always look for a simple solution rather than assume the complex. Learned that from many years of practical experience with all sorts of things mechnical.

"Assumptions" often cost lots of $$$$$$$$$$$$$$$$$ in wasted expense. Very Happy

engine049 Mon Mar 19, 2012 10:00 am

Here's a way to check to see if your cylinder is leaking. Remove piston and cylinder, w/ glowhead removed put some spit on your finger stick it on top of the cylinder and push piston in and out check for compression that way. helps to have a good peewee cyl piston to know what it feels like. Someone could have removed a glowhead gasket previously at the factory with a pick or came off a test engine or mis-machinig from the factory. Any number of things could be wrong. I always advise everyone get a $2 30x magnification loupe. http://www.ebay.com/itm/30x-21mm-Jewelers-Eye-Loupe-Magnifier-Magnifying-glass-/160550823275?pt=LH_DefaultDomain_0&hash=item256193256b

$1.98 shipped to usa

**Cribbs74** Mon Mar 19, 2012 10:15 am

SuperDave wrote:Ron:

As always look for a simple solution rather than assume the complex. Learned that from many years of practical experience with all sorts of things mechnical.

"Assumptions" often cost lots of $$$$$$$$$$$$$$$$$ in wasted expense.

Good point Dave, thing is there are about 4 things that can cause bad compression in a Cox engine. All very simple....... piston to cylinder fit, leaking around head gasket, leaking through head itself and improper head sealing surface.

Matt did have a good point about the old oil residue though. Going to check that out tonight.

Mudhen Mon Mar 19, 2012 10:29 am

dankar04 Mon Mar 19, 2012 10:37 am

Years ago I bought a new in box TD .020 just because local H/S had one. Got it home and put prop on it. Low compression. Filled tank and gave it a go. Engine did start right up and ran strong. I did not push it but it ran very good. Next check compression and it was good as it should be. Ron like Matt said maybe threads have residue and need work. Both types of .020's should have good compression.

**Cribbs74** Mon Mar 19, 2012 10:59 am

Matt, Mud, Dan, Dave and Tom,

All very good info, thank you for taking the time to reply. I guess I have more work to do than I thought!

Ron

Surfer_kris Mon Mar 19, 2012 11:03 am

You can check the head for leaks by spraying soap-water on it, a head leak will give bubbles when engine is turned over.

A poor piston to cylinder fit can sometime be seen as bubbles in oil at the exhaust ports. A drop of pure castor oil in the exhaust port can also temporarily seal the piston/cylinder and be used for diagnostics.

John Goddard Mon Mar 19, 2012 11:32 am

I'd be interested in a solution Ron.

I bought that NIP 010 piston and cylinder b4 Xmas that was the same.
I got the 'other' 020 set from Bernie I'd better take a look I guess.

**Cribbs74** Wed Mar 21, 2012 7:52 am

John Goddard wrote:I'd be interested in a solution Ron.

I bought that NIP 010 piston and cylinder b4 Xmas that was the same.
I got the 'other' 020 set from Bernie I'd better take a look I guess.

Ok,

Quick update, my compression is much better. I basically followed Mud's and others suggestions and lo and behold it worked. There was no obvious sign of gunk etc but, after a good cleaning of the cylinder to include threads and 000 steel wool. Also a polish of the piston, new gasket the compression appeared. It's not awsome but at least the prop will pop over and slap my finger now. Before it just spun right through TDC.

So John, just go through Mud's and others suggestion and see what happens!

I use Never Dull to polish the piston. Not sure what they call it in the UK. Basically it's cotton wadding impregnated with some polishing solution.

I think another break in is all I need to make it perfect.

PV Pilot Wed Mar 21, 2012 8:37 am

cribbs74 wrote:
John Goddard wrote:I'd be interested in a solution Ron.

I bought that NIP 010 piston and cylinder b4 Xmas that was the same.
I got the 'other' 020 set from Bernie I'd better take a look I guess.

Ok,

Quick update, my compression is much better. I basically followed Mud's and others suggestions and lo and behold it worked. There was no obvious sign of gunk etc but, after a good cleaning of the cylinder to include threads and 000 steel wool. Also a polish of the piston, new gasket the compression appeared. It's not awsome but at least the prop will pop over and slap my finger now. Before it just spun right through TDC.

So John, just go through Mud's and others suggestion and see what happens!

I use Never Dull to polish the piston. Not sure what they call it in the UK. Basically it's cotton wadding impregnated with some polishing solution.

I think another break in is all I need to make it perfect.

Good News!,,congrats. Have used the Nevr-dull before and it's good stuff for a quick scrub. It's more of a extra fine abrasive solution in that stuff. I have the Heavy Metal polishing stuff I always post about in the cotton wad as well. A wad of the red coarse abrasive for the first cleaning/roughing, then finish polish with the medium green.

Kim Wed Mar 21, 2012 9:34 am

Ditto here! Another Mud Hen instructional note gets copied and stuck in the shop book! The gooey .020 that came with my Mini Stunt is about to receive the "Mud Hen Treatment" !!!!

John Goddard Wed Mar 21, 2012 11:43 am

I use Never Dull to polish the piston. Not sure what they call it in the UK. Basically it's cotton wadding impregnated with some polishing solution.
.[/quote]

Duraglit, Brasso or (don't laugh) Goddards

So, Metal Polish, Veterinary Surgeons, Rocket Scientists then me.
lol!

PV Pilot Wed Mar 21, 2012 11:50 am

John Goddard wrote:

I use Never Dull to polish the piston. Not sure what they call it in the UK. Basically it's cotton wadding impregnated with some polishing solution.
.

Duraglit, Brasso or (don't laugh) Goddards

So, Metal Polish, Veterinary Surgeons, Rocket Scientists then me.
lol!

[/quote]

LOL!

So, Metal Polish, Veterinary Surgeons, Rocket Scientists, Hot dog vendor, then me.
(3 steps forward, and one back for me, Very Happy

)

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