IC engine valve troubles

[Lakc]

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.

 

[gbritnell]

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

 

[RonGinger]

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.

 

[gbritnell]

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

 

[jpeter]

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.

 

[RonGinger]

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.

 

[stevehuckss396]

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

 

[Swede]

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

 

[RonGinger]

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.

 

[gbritnell]

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

 

[pcw]

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

 

[jpeter]

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