Author Topic: NOS engine has very little compression, What to do? (Read 4571 times)

frank mccune · « **on:** April 17, 2016, 06:05:55 PM »

Hello All:

Perhaps someone may offer some guidance as what to do with this engine. It is a HP. 40 F circa 1971. Perhaps a Silver Star that had been converted to CL by adding a venture, nva and a gold head from the HP Gold Cup.

Here are a few notes that I made concerning this engine:

The engine has never been run before I ran it yesterday. I ran about two quarts through it in a rich 4 cycle while speeding the engine up for a few seconds to raise the temperature. The engine was permitted to cool to ambient temperature between runs. I have had other ringed engines that had very little compression when new but they improved as they got more run time. This engine did not indicate that it would get better with more run time. The cure for these engines were a new ring made and fitted by Mr. Bowman.

The compression is very poor and can only be started via an electric starter.

The cylinder looks very good as it still has the crosshatches in the cylinder bore and no indication of ever been run.

The ring appears to fit very well. The gap looks very good and the ring is very smooth on the perimeter.

The piston is also pristine with no rub marks or burrs. The piston groove is in great condition.

I used a new ring to check the cylinder for concentricity and proper end gap and all looked good.

One thing that I did notice was that the fuel would not come to the engine when being choked. I have had this problem with other engines that had very low compression. Perhaps if there low compression, there is also very little vacuum in the crankcase to pull fuel from the tank while being choked.

Once running, the engine appears to run very well.

I had the same problem with another HP .40 that was cured by a trip to Mr. Frank Bowman who fitted a new ring. Now, it starts first flip every time! It is a shame that he no longer offers his services! Is there anybody that does rings and engine as he once provided?

Suggestions or comments.

Tia,

Frank McCune

Tim Wescott · « **Reply #1 on:** April 17, 2016, 06:17:22 PM »

If the engine were converted, run "just once" and then sat around for decades, the ring might be stuck in the groove with gummed-up castor oil. If that were the case then you might be able to free it up with any of the usual means of removing castor gum.

Or, it's all hosed and you need to call Mr. Bowman.

RandySmith · « **Reply #2 on:** April 17, 2016, 06:50:20 PM »

If the motor is in as good of shape as you said, it will have good compression unless the ring is stuck, or damaged, BUT many times these have been taken apart, and the sleeve is bent or warped removing the sleeve...( same with ST engines) I have seen that a lot, Also sometime people run them in a peaked 2 cycle, ruin/flat spot the ring ( this is very hard to see), you should put a new ring in it and square it with the piston, pull the piston out and look with a strong light to see if the ring it touching the sleeve all the way around...full circle..

In addition when checking a new one flip it backwards to check compression

I have new HP 40 rings, and I believe Mecoa does too. I also may have some of my Special lapped ABC setups for the HP 40

Randy

frank mccune · « **Reply #3 on:** April 18, 2016, 05:18:57 AM »

Hello Randy and Tim:

Thank you for a quick reply to my latest engine drama.

Let me add some information to what I have already posted:

The engine has the same amount of compression when flipped in either direction.

I did use both the original and the new ring to check the fit in the cylinder. I could not see any light around the rings when they were inserted into the cylinder.

I did clean and inspect the ring groove while the ring was removed. All was well. One must note that the ring is pinned on this engine and one can not rotate the ring in its groove to check for a defect. One may take a ring and walk it around the ring groove to check for groove damage. I found no defect while doing this.

I doubt that additional running of this engine a will be of any benefit. I hope that I am wrong about this. I may fly it in a large, 500-600 sq. in. stunt plane today just to see if things improve. I have never been fortunate enough to have poor fitting piston rings "run in" and have a good fit. This includes cars, trucks, lawnmowers and model airplane engines. Replacement always solved the problem.

In closing I again want to thank you guys for taking the time and effort to offer advice. If you can think of any other tidbits of information, kindly post them.

Be well,

Frank McCune

ps. Tim, Mr. Bowman ceased making rings several months ago. Perhaps someone will pick up his business and continue making rings.

Avaiojet · « **Reply #4 on:** April 18, 2016, 12:01:09 PM »

Quote

I ran about two quarts through it in a rich 4 cycle while speeding the engine up for a few seconds to raise the temperature.

Frank,

Why did you do this? Did you read this someplace on "How to brake in a ringed engine."

Charles

Lauri Malila · « **Reply #5 on:** April 18, 2016, 01:10:29 PM »

Frank,

Does it have a Dykes ring? I remember reading somewhere that dykes-ringed engines have poor compression when engine is not running.
I made dykes rings in our latest engines but must have done something wrong, compression is as good as with a standard ring.
Does the engine show signs of low power or overheating when running?

Lauri

Steve Helmick · « **Reply #6 on:** April 18, 2016, 02:52:47 PM »

I don't have any experience with the HP engines, but my T&L rebuilt (new CL cylinder & Bowman ring) G.51 had NO compression after a dozen or so runs and maybe half a dozen flights. I was benching this engine up in BC, and got Alan Resinger to look at it, because I knew he'd flown ST .60's for some years. We decided to pull the head off and there were random shiny spots on the cylinder, and I didn't see any signs of a cross-hatch anywhere.

As a retired machinist and having suffered 10 years in QC, which included plenty inspection of honed bores, I feel qualified. So, I asked Alan about the idea of roughing the cylinder with a brake cylinder hone, and he agreed that it might help. When I got back home, I pulled the engine apart and ran the brake hone through the cylinder a few times, putting a nice cross-hatch on it and removing the shiny spots. I emailed T&L about this, and it was not...shall I say...well received. I really don't think the cylinder got honed at T&L (he had that outsourced).

Last flew that engine/plane in Aug. 2010 in Edmonton, just a few weeks after the above episode. Until last October (5 years later!), it finally started showing signs of compression. Previously, it felt very much like an electric motor. I'm not sure if any of this will help, but I hope so.

Steve

Tim Wescott · « **Reply #7 on:** April 18, 2016, 03:40:37 PM »

Quote from: frank mccune on April 18, 2016, 05:18:57 AM

ps. Tim, Mr. Bowman ceased making rings several months ago. Perhaps someone will pick up his business and continue making rings.

Uh, call him and be really convincing?

I didn't get the part where you said you'd already replaced the ring -- sorry.

RandySmith · « **Reply #8 on:** April 18, 2016, 04:02:51 PM »

Frank if you have it apart and want to, send it to me, i will check it for roundness, and the ring and piston, I can also check the ends where many people ding the ring by hitting one of the ports, i can also check the inside case bore for you

Randy

frank mccune · « **Reply #9 on:** April 19, 2016, 07:30:01 AM »

Hello All:

After much thought about my dilemma, I have decided to fly this engine for awhile as it is and hope for the best. It responds instantly to an electric starter and seems to run very well. There is no overheating or loss of power as it establishes operating temperature.

This engine, .40F or perhaps Silver Star, has an aluminum piston with one conventional ring riding in a hardened steel cylinder. No Dykes Ring as I interpret the definition for a Dykes Ring, on in this engine.

If this does not work well, I will install a new ring. Perhaps I should do first! It may be the egg vs. chicken argument. Comments regarding replacing the ring now or later.

I recently replaced the rings on a 1948 McCoy .29 Sportsman that had very little compression after the new rings were installed. However, after running the engine on the bench. the compression improved to be very good. So. there may be hope for the HP.

Thank you to all who replied to my post.

Be well my friends,

Frank McCune

Bill Johnson · « **Reply #10 on:** April 21, 2016, 09:26:50 AM »

Quote from: frank mccune on April 19, 2016, 07:30:01 AM

I recently replaced the rings on a 1948 McCoy .29 Sportsman that had very little compression after the new rings were installed. However, after running the engine on the bench. the compression improved to be very good. So. there may be hope for the HP.

I think that's normal, Frank. The ring has to wear in to match the grooves on the liner before compression comes up. That's why on full size air-cooled aircraft engines, the first 10 hours of run time is done on straight mineral oil.

I think you'll be in good shape.

frank mccune · « **Reply #11 on:** April 21, 2016, 04:26:49 PM »

Hello:

A big thanks to all of you who responded to my break in dilemma.

I have been running a HP .40 Gold Cup this week to get enough compression to hand start it. Today the engine got a good enough ring/cylinder seal to enable me to hand start it on the first flip when cold. I accomplished this by running the engine a fast 4 cycle using a 10x3 plastic prop and fuel with 20% castor 5% synthetic and 5% nitro and the rest alky. I did the last three runs with the stock muffler attached. Not what I preferred but it kept the neighbors happy.

Now on to the Silver Star. It will receive the same treatment and if it does not respond well, then I will try a new ring.

Be well my friends,

Frank McCune

John Leidle · « **Reply #12 on:** April 21, 2016, 04:55:45 PM »

I rehoned HP when I felt the compression was low ,, after I did it still had low compression but runs good.
John

bob whitney · « **Reply #13 on:** April 21, 2016, 08:29:13 PM »

a brake hone is ok if u know the cyl is round to begin with , if it has hi spots the brake hone will just follow the cyl. u need something like a sunnen hone to remove the hi spots.

i was given a new,old S/T 60 in pieces,when i put it together it didnt have any comp .after tearing it back down ,found 4 shiny spots . put it on the sunnen hone then checked for roundness and re assembled it and it has great comp now

Bill Johnson · « **Reply #14 on:** April 21, 2016, 10:01:24 PM »

Quote from: bob whitney on April 21, 2016, 08:29:13 PM

a brake hone is ok if u know the cyl is round to begin with , if it has hi spots the brake hone will just follow the cyl. u need something like a sunnen hone to remove the hi spots.

i was given a new,old S/T 60 in pieces,when i put it together it didnt have any comp .after tearing it back down ,found 4 shiny spots . put it on the sunnen hone then checked for roundness and re assembled it and it has great comp now

Bob, do you think a brake cylinder hone would work also?

Brett Buck · « **Reply #15 on:** April 22, 2016, 09:53:49 AM »

Quote from: Bill Johnson on April 21, 2016, 10:01:24 PM

Bob, do you think a brake cylinder hone would work also?

Before anybody goes crazy, the purpose would be to merely *rough up* a shiny spot, should it appear. This is to mitigate the effects of the mirror-smooth local finish that sometimes gets polished onto the cylinder as noted by Scott Bair in his classic paper.

It takes about 10 seconds at the very slowest you can turn it - I used to turn it by hand. You don't want to take off any consequential metal or you will very likely damage the cylinder beyond repair. And only on ringed engines with iron or steel liners. Any use on a ABC/ABN/AAC engine will only ruin it immediately.

Brett

Glenn (Gravitywell) Reach · « **Reply #16 on:** April 22, 2016, 10:16:48 AM »

I have an old schneurl(sp) ported Irvine engine that actually windmills when it stops running while flying. It has never had compression and you have to start it with an electric starter. But once started it pulls like a bear! Compression is overrated!LOL

RandySmith · « **Reply #17 on:** April 22, 2016, 01:20:47 PM »

You can lightly hone Steel sleeves , and you need to go slow while moving the hone up and down the sleeve, then reverse ends and do the same... this is a "FEEL" thing and you do NEED to go slow until you know what your doing, you can ruin a sleeve doing this
The steel sleeves, Chromed sleeves , ABC and AAC can be honed, they are tougher than steel sleeves and typically take longer, DO NOT ever do a OS ABN sleeve , as it is so thin and soft you will ruin the sleeve very quickly.
Never keep the hone still, in one place, your trying to just lightly cut very small thin spiraling swirls that twist up and down into the sleeve, and buff out shiney spots, try to pay attention mainly to the middle and upper part of the liner, as this is what polishes most

Randy

Author Topic: NOS engine has very little compression, What to do? (Read 4571 times)

frank mccune

NOS engine has very little compression, What to do?

Tim Wescott

Re: NOS engine has very little compression, What to do?

RandySmith

Re: NOS engine has very little compression, What to do?

frank mccune

Re: NOS engine has very little compression, What to do?

Avaiojet

Re: NOS engine has very little compression, What to do?

Lauri Malila

Re: NOS engine has very little compression, What to do?

Steve Helmick

Re: NOS engine has very little compression, What to do?

Tim Wescott

Re: NOS engine has very little compression, What to do?

RandySmith

Re: NOS engine has very little compression, What to do?

frank mccune

Re: NOS engine has very little compression, What to do?

Bill Johnson

Re: NOS engine has very little compression, What to do?

frank mccune

Re: NOS engine has very little compression, What to do?

John Leidle

Re: NOS engine has very little compression, What to do?

bob whitney

Re: NOS engine has very little compression, What to do?

Bill Johnson

Re: NOS engine has very little compression, What to do?

Brett Buck

Re: NOS engine has very little compression, What to do?

Glenn (Gravitywell) Reach

Re: NOS engine has very little compression, What to do?

RandySmith

Re: NOS engine has very little compression, What to do?