# IC engine valve troubles



## RonGinger (Sep 4, 2011)

Many years ago I built a 4 cylinder engine, mostly following the PANTHER PUP design. I made it water cooled, so the block and head are completely my design.

It eventually ran, but I had a tough time getting the valves to seal, and I dont think I ever got all 4 cylinders to fire. I ran it at shows for a few years, but it eventually refused to start.

Today I decided its time had come, so I tore it apart 

I first tried to measure compression. I made an adapter to fit my car compression tester, but all I got was a needle flicker, no pressure at all. I suspect the total volume of the air in the hose and gauge is much more than the displacement of the engine, so it doesnt read.

Has anyone found a way to measure compression of a 1" bore cylinder?

My valves all show a shiny ring that looks like a reasonable seat, and no signs of any leak spots.

The valves are tight fit in the valve guides. I have read that loosening that fit can make a valve seat better. Anyone have experience with that?

Should I try to lap the valves in, as with big engines? I have heard this causes more problems with small valves because the seat becomes to wide and the effective pressure is to low to seal/

Im thinking about installing the head and using shop air through the spark plug hole to pressurize each cylinder an see if there are any leaks. Has anyone tried this?

Id like to get this thing running again.


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## stevehuckss396 (Sep 4, 2011)

How wide are the seats. To get a tiny valve to seal the seat needs to be as thin as .010 wide. If you need to lapp the valves use a very high grit number compound. Try 5000 or something. You are correct that normal compound will only make it worse. Brian Rupnow built the Kerzel hit and miss and had a terrible time with the valves. Take a look at his thread for do's and donts.


As far as the compression tester goes, I have seen articles and I think on this board where a check valve was installed between the cylinder and tester. The volume of the mini cylinder is the problem. The check valve will allow you to "pump up" the tester to get a more accurate test.


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## deverett (Sep 4, 2011)

Jan Ridders designed a simple compression tester.

http://modelengineeringwebsite.com/Compression_tester.html

Dave
The Emerald Isle


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## Brian Rupnow (Sep 4, 2011)

Stevehucks is correct. I had a terrible trial with my Kerzel build, but eventually I did get the valves to seal. I think the final solution was to build a valve seating tool which was posted by one of this forums talented members. There is information in my thread about the tool, and a link to the tool builders original thread.---Brian


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## gbritnell (Sep 4, 2011)

Hi Ron,
The only reliable way to check valve leakage is with vacuum. That being said here's what I do. Make some type of adapter to fit over your port or a tube that will taper fit into your port. Once done just suck on it. If it will not hold a vacuum then you have a problem. Generally the problem will be with the seat area. As Steve said, use a very fine grit lapping compound and just slowly work the valve against the seat. To do that I chuck the stem end of the valve with my small hand chuck and after applying a small amount of compound to the seat area I spin the valve with the chuck (by hand). You want to rotate it back and forth a few times then lift the valve from the seat and rotate it to a new position and repeat so that you are hitting a different high spot. 
One thing you don't want to do is enlarge the valve guide hole. If you do you will draw air through there and it will make it almost impossible to check. One way that will help if your guide hole is too big is to insert the valve and then put a ring of grease around the top of the stem and the valve guide. This will seal it up enough to be able to apply vacuum to it. 
After lapping it for a short time, pull the valve out, wipe all the grit off the seat and the valve and look to see if there is a nice uniform gray color to both surfaces. If so then try the vacuum test again. Believe me when you get it right you will not be able to suck through the port. 
 As far as a compression testing device, I have tried several different methods but not with much success. 
 The better automotive type testing devices have a check valve down near the spark plug adapter. The cheap ones don't. The reason to have it as close to the adapter as possible is that you are not adding the volume of the hose to the volume of the cylinder. On an automotive engine the additional volume is negligible but for small engines, motorcycles, lawnmowers etc. it does make a difference. This is almost impossible to do with our small engines. 
George


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## Rustkolector (Sep 4, 2011)

Rather than compression, I prefer using vacuum to test valve seating. I use a simple brake bleeding vacuum pump kit sold at Harbor Freight. It is done easiest with the head(s) removed. Lubricate the valve stem with heavy oil. With the valve springs installed, pulll vacuum on the intake or exhaust port. You should be able to pull down to about 25" hg on the gauge. If the gauge doesn't drop below 20" in 10 seconds, you have about the best seal you can ever expect, but that degree of seal is not needed for good operation. As Steve has said, a narrow seat is preferred and will seal easiest. I use 800 grit grinding compound. If that doesn't seat a valve in a few tries, the seat is probably not concentric with the guide bore and will need to be recut. Specially made seat cutters that use a pilot are best. 

Jeff


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## Lakc (Sep 4, 2011)

For a compression tester I used the smallest pressure gauge I could find, and made the shortest 1/4-32 to 1/8 pipe adaptor that could clear the head, worked like a charm without a check valve. It wasnt hard to tell where the needle peaked even as it was swinging. You are correct, volume is the enemy.

I used regular permatex valve lapping compound, but I wouldnt recommend it for most model engines. I have ground tool steel seat inserts and dual valve springs so stiff I can barely compress them with my thumb. Its not a common model setup.

I made a leakdown tester and tested the seal with compressed air. That worked fine for large leaks but not so well when they got smaller. 

The best leak tester I used was my finger. If you cover the exhaust port and it leaks you will feel it suck against your finger on the intake stroke. Cover the intake port and you feel it blow on the exhaust stroke. I knew I had it right when I felt the compression at the exhaust port as the exhaust valve opened.


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## RonGinger (Sep 4, 2011)

Thanks for all the response. I have also re-read Brians kerzel post, and looked at Georges seat cutting tool.

I think I have a plan now, tomorrow Ill get on it.

thanks everyone

ron


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## Swede (Sep 6, 2011)

There is a brand of lapping compounds called "Time Saver" that is engineered and guaranteed NOT to embed. Whenever I am concerned about being too aggressive with grinding compounds, I go for the Time Saver. It seems to be a lot more forgiving and gentle than typical ALOX or silicon carbide pastes.

I also agree that loosening up the valve stem to guide interface can work wonders. We tend to dislike doing this, but sometimes the reality is that looser tolerances work better. I think 0.0015" to 0.002" is good for typical model engine valve stems of 0.125" or 0.156".

Time Saver: http://www.ws2coating.com/timesaver.html


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## RonGinger (Sep 6, 2011)

My head is a flat plate so I was able to take a light facing cut across it and remove all of the old valve seats from the cages, so I had nice square end brass cages.

I made a cutter like George suggested and cut a nice small seat. The cutter worked very well, it was a firm fit in the valve guide so I think the seats are good and concentric.

I lapped each seat with a 320 grit compound. I timed the first couple and was lapping for 1 minute. You can hear the sound change when the lapping stops cutting. I think I got a little hasty on the later seats.

I tried sucking on a plastic tube in the ports and thought I had a reasonable seal. When you pressed the valve to release it there was a clear snap to it.

I put it all back together, made a new head gasket and now I seem to have lower compression than I did before I started.

I think I also discovered why it stopped running- the carb and fuel tank was a mess of brown, sticky gunk from old fuel. Ive cleaned all that up now.

This morning I bought a hand vacuum pump kit with a bunch of tubing fittings. I have not tried it yet.

I think I may put it all back together, make a nice static display out of it, and go back to making steam engines.


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## Lakc (Sep 6, 2011)

RonGinger  said:
			
		

> I put it all back together, made a new head gasket and now I seem to have lower compression than I did before I started.



You shaved the head, did you relash the valves?


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## RonGinger (Sep 6, 2011)

Yes, I did re-set the valve clearance.

I have now tested with the vacuum gauge. The best ones will pull to about 20", then take 7-8 seconds to drop to zero. Some that were fast drop I have re-lapped to get to the 7-8 seconds drop.

I tested one while it still had lapping compound on it and it held solid at 20", but thats just the effect of the compound making a seal.

Is a 7-8 second drop good enough?


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## Brian Rupnow (Sep 6, 2011)

Ron---I ended up using 400 grit followed by 600 grit when I hand lapped the Kerzel valves, after using the valve seat cutting tool.----Brian


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## stevehuckss396 (Sep 6, 2011)

RonGinger  said:
			
		

> I lapped each seat with a 320 grit compound.



Ron, Take another swipe, recut the seats, install the valves and start the darn thing. When you lapp you damage the seats. I never lapp anymore.


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## Lakc (Sep 6, 2011)

Sorry Ron, I had to ask. 

Like Steve said, run it and see how it goes.


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## stevehuckss396 (Sep 6, 2011)

aermotor8  said:
			
		

> how does lapping damage the seats?? ???



It scratches them all up. If you cut the seats and get a good finish, and do the same with the valves, then the 2 smooth surfaces will seal. That us if they are concentric with each other. When I made the V4 i kept lapping with everything under the sun. Nothing but trouble. New seats with a new boring bar, recut the valve surface with a brand new bit, install both and started right up. Works for me. Could work for him to.


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## Swede (Sep 8, 2011)

I think it boils down to the grit used. Typical "Clover" brand, the stuff you'f sind in an auto supply store, is going to be way too coarse for these tiny valves and seats.

When you think about it, a polish like "simichrome" is a form of lapping compound. Anything with abrasive in it will cut metal. Good mild abrasives might be toothpaste, as mentioned, rubbing compound, rottenstone mixed with oil, jewelry polishes, diamond, etc. The thing to avoid is lapping the actual valve with the seat, as traditional abrasives embed; that's how they work. But you can do this with the Time Saver compounds, and it does indeed work very well.

Whatever works is good, but I think it's a disservice to say that "lapping won't work" and likewise "boring and turning alone won't work." Both have advantages and disadvantages.


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## stevehuckss396 (Sep 8, 2011)

Swede  said:
			
		

> but I think it's a disservice to say that "lapping won't work"



Didn't say it won't work. All I'm saying is if you get a good finish on the mating parts it's unnecessary.


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## stevehuckss396 (Sep 8, 2011)

aermotor8  said:
			
		

> steve could you let us know what you used (pictures please) and how you did what you did to get your valves to seal?
> 
> it sounds most interesting to make valves that seal without lapping.
> i know i have never made a valve that would seal without lapping and i would like to know how cause lapping is messy and time consuming.
> ...




Here you go! Pages 19 - 22 shows the valve cages and valves being made. You will see the tiny boring bar used to cut the seats. It's razor sharp and left a REAL nice finish. No lapping, no testing, just put them in and started it up.

http://www.homemodelenginemachinist.com/index.php?topic=9609.270


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## Steve_Withnell (Sep 8, 2011)

Hmmm.

I made the Nemett 15s and could not get the valves to seal. The advice was not to lap. I did in desperation, I used "brasso" which is a brass / copper polish in the UK. It did not improve the seal and it did cause circular scoring in the seats (as per advice not to lap).

I found an article from a ex Rolls Royce engineer, whose practice was to cut the seat at two different angles - 30 & 60 degrees.  The aim is to get a concentric edge at the boundary of the two angles in the middle of the seat. So I did that (not too big a deal with only two seats to recut) and made I thought, a nice job. Still no compression.

So - (I've posted this previously)  I put a small quantity of 20/50 engine oil in the cylinder. Spun the engine up, it fired a couple of times and then a load of compression appeared by magic. Its how my Dad taught me to get the drop on old diesels with low compression that wouldn't start. May be it worked maybe I just got lucky, but that's my story!


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## Lakc (Sep 8, 2011)

Steve_Withnell  said:
			
		

> it fired a couple of times and then a load of compression appeared by magic.


I worked with a guy that swore the valves broke in better when he left lapping compound on the seats, but then he could never get them started, and I am talking 2.2L of automotive engine. 

I eventually got his motors started with compressed air, blown between my fingers with my hand covering the throttle body. Same effect, once it fired a few times, it had compression.


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## gbritnell (Sep 8, 2011)

Gentlemen,
Ideally, and I say ideally one should be able to cut the seats and the mating valve surfaces and have them seal. Now we're talking high precision in machining. The guides would need to be exactly concentric with the seats. The seats would have to match the angle of the valve perfectly and the valve sealing surface would have to be concentric with the valve stems. 
 The valves should be the easy part of the equation. Chuck up a piece of stock, cut the stem, head and seat all in one setting. Now cut it off, rechuck it and cut the head of the valve to the desired thickness.
 Now the seats and guides. Here again one would think that doing the whole affair in one setting should give almost exacting results. The only process that could be off would be that of the valve guide. For working on these small engines normally one starts out by center drilling the piece of stock followed by an undersized drill and lastly with the appropriate reamer. If there's going to be a variable this is where it will be. I would propose making a tool from drill rod that would follow the undersized drill and open the hole up to just a few thousands under the reamer size. This tool would only need a small clearance groove for the chips and would be rigid enough to true the hole prior to reaming. The next operation would be to bore the port and finish off by cutting the seat surface. 
 Now the finished valve guide/port/seat piece gets pressed into the head. Some have found that this operation can also cause problems. Even with small press numbers (.0015-.0002) there can be some distortion to the piece and there goes the exacting precision. 
 As has been discussed and tried I feel that by making a seat cutter with everything machined concentric a person stands the best chance of having a 'machined seal' to their valves. 
 Personally I don't feel that by using a very fine grade of lapping compound is a detriment. If the machining is 'close' then the compound is just taking the high spot off (.0002 ?) Yes if you use a coarse grade of compound you are going to get rings in your seat or on your valve. Remember these are generally soft materials so they score quite easily. 
 The bottom line is this is one of the most crucial machining operations in building an internal combustion engine and extra attention should be paid to your setup, tooling and fits. 
 It's not impossible, lots of fellows do it. Just take your time and be patient. 
George


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## RonGinger (Sep 8, 2011)

I did resort to lapping, with Timesavers fine. I got all the seat to pull a vacuum of 20", then to bleed down in 7-8 seconds.

I put the engine back together and tried to start it. After a while I was able to get one cylinder to fire pretty well. I tried a few things but nothing seemed to make the other cylinders go.

I decided to take the spark plug from the cylinder that was working and move it to another cylinder. That cylinder now fired.!

So it looks like I now have a spark plug problem. I have started a new set of plugs. The old ones were pretty crude, using a 'surface gap' instead of the conventional ground strap. 

I wont have much time tomorrow, but in a day or two Ill have new plugs.


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## gbritnell (Sep 9, 2011)

Hi Ron,
First off I'm glad you got the valve seal problem licked. 
Isn't it funny how we concentrate on one area and sometimes overlook something else. I've done it many times myself. Spin the engine over a million times, one plug fires, move it around and it still fires. I've done this thinking at times it was the plug only to find out that the fuel mixture was wrong and for some reason only one cylinder would fire. Don't ask! 
That's what people don't understand when they see one of these little things running. 
Oh, it must be like a model airplane engine, they run so this should run. They don't know the hours of work that went into valve seating, spark plug making and carburetor settings. 
 I guess that's what makes it so satisfying for me, finally getting one of these to run half-way good. 
George


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## jpeter (Sep 10, 2011)

I've had good success lapping with 600 clover compound and also with tooth paste. When I seat valves in aluminum heads I use tooth paste. I worry about alox compound embedding in aluminum. I test by blowing air, hose in mouth, into the combustion chamber through the sparkplug hole, fuel tubing works well, while I hold the head under water. I make an adaptor from an old spark or glow plug. I make a cover to go over the combustion chamber to keep the air from escaping although on small chambers you could use your thumb. If I see a bubble form more often than every 5 seconds I feel the valve isn't sealed well enough. Seems like trying to hold a vacuum would introduce too many variables like leakage around the stem, which on exhaust valves doesn't affect running much. With in reason I don't think intake valve stem leakage means much either. Means a lot though, I would think, on the vacuum test.
 Although I've never tried it, the leak down test is getting kinda popular. Seems you put a certain pressure through the sparkplug hole into the cylinder then time how long it takes the pressure dissipate. Seems like a good way to compare cylinders.


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## RonGinger (Oct 3, 2011)

*It Runs!!!*

But I guess the problem was not valves after all. I did re-do them, and got good results from the suggestions here. But while trying to start the engine I realized only one cylinder was firing, and if I moved that spark plug the working cylinder moved.

My original spark plugs were simple, with no ground strap, just what I think is called a surface gap base. 

This weekend I made new plugs, from corian, as detailed here in several threads. I glued them with 5 minute Locktite epoxy. After a couple hours waiting I tried to run the engine, and it fired up almost instantly and ran great. I only let it run a few seconds, since the epoxy was still probably not fully cured.

[ame=http://www.youtube.com/watch?v=x9GEb1wudiw]http://www.youtube.com/watch?v=x9GEb1wudiw[/ame]

Today Ive given it a few more runs. It has some carb problems, but I think I'm going to declare this engine done. Its got several design problems that will keep it from ever being a great engine, so I am going to just wrap it up in a way I can run it at shows and declare it finished.

On to my model Steam launch so I can take it to Cabin Fever in January.


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## stevehuckss396 (Oct 3, 2011)

I'm glad you got it going. Shows what can happen if you keep at it.


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## Swede (Oct 3, 2011)

I'm glad it's running well for you, Ron. Beautiful engine, presented very well!!

Troubleshooting IC engines is always a bit of a trip. In a way, it can be fun as well as irksome... so long that in the end, you get success. And it's always a big issue with multicylinder engines in that as the number of cylinders goes up, the odds that one (or more) isn't firing also goes up, and that can drive a guy NUTS. No rest until every cylinder is firing. Then, you start to wonder and worry about uneven firing - and you keep on plugging away.  ;D


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## RonGinger (Oct 3, 2011)

I just looked back at my web page http://plsntcov.8m.com/pup.htm and see the engine first ran on Aug 13, 1995. 

I believe this was the first model engine to have its sound on the web. I had my web site starting about 1994, and I posted the engine article when I got it running. In those days there were no video formats on the web, http V1.0, but I put up a .wav sound clip. The photos were all .gif files, .jpg was not yet in use. I lost that file in a server move years ago, but I still have the rest of the page.


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## gbritnell (Oct 3, 2011)

Congratulations Ron,
With a little fine tuning on the carb it sounds like it would be an excellent runner. It sounds like it hits nice and evenly albeit a little fast but that's another whole can of worms. Maybe we'll get to see it at Cabin Fever.
George


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## pcw (Oct 4, 2011)

hmmm so it wasnt realy the valves, but the sparkplugs? 
i dont know that huge amount of IC engines, but isnt this something other builders might try before spending weeks or longer fidling with valves?
pascal


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## jpeter (Oct 10, 2011)

Good job. Anyone that gets one running is ok in my book.


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