Possible Stuart 7A Engine

[Mfoxchicago]

Hey Guys,
My boat has a small auxiliary steam engine aboard that drives the makeshift Genset. However, it makes a damn annoying knocking sound when its run up to speed.

First, is there any place on the engine, other than the valve chest housing would I find some sort of manufacture's stamp?

Second, I assume with a bit of guideance I should be able to adjust the timing settings a bit to cancel out that knocking noise and reduce the stress on this engine so I might run it up to speed. I really need the charging of the battery to happen whenever we're out steaming for my shore power access is non-existent.

Thanks,

[fredrosse]

For a double acting engine, the knocking is usually due to excessive bearing clearances. This is inherent for double acting engines, either the various shaft bearings (Connecting rod big end, small end, or mains), or crosshead slipper. Any loose clearances here must be corrected to stop knocking.

Changing valve timing will not help in general, unless you convert a double acting engine to a single acting engine. This modification is simple enough, but you will lose half the engine's power, usually not a good idea. Better to just fix the running clearances for your engine.

[Mfoxchicago]

Thanks for the education Fred. Any Youtube or articles you'd recommend to help me become familiar with the engine parts you described and how I might begin ascertaining the true imbalance. I have no intentions of converting to a single action, will use a it has been, just want to clean up that "knocking".

[Mfoxchicago]

Fred, I really hope you can make it down this way in the summer. Since we both are Walking Beam Engine owners, I'd love for you to see TULE's 20hp Engine. She is amazing!

[Lopez Mike]

I don't think Fred was suggesting that there was an imbalance, though there is always some imbalance by the nature of the beast. I have found two sources of knocking in these engines. One, the much less common one, was a combination of way too close a clearance between the piston and the cylinder heads combined with the piston getting slightly loose on the piston rod. I have heard of the piston not being centered on the rod thus causing it to touch one cylinder head and not the other.

Far more common is some wear creating slack on some bearing that has reversing loads. The crosshead and wrist pin area is the most common offender. 6A Stuarts are notorious for the cylindrical cross head wearing out. Re-machining followed by hard chroming followed by having the fit being done on an automotive pin honing machine has worked for me.

The rod big end might be loose. Sometimes there are shims under the rod cap and you can take some out carefully in small increments. There is a nice product called Plastiguage that helps get the clearance right.

Seldom, but once in a while, the main bearings are worn.

Probably something is loose. Pull the top head. See if you can attach a hunk of threaded rod to the piston rod where is comes out of the piston using a coupler nut. Or remove the piston keeping the rod in place. Yank up and down on the piston rod with the crank in various positions and look and listen for slack.

I wouldn't fool with valve timing. I could be wrong but look for wear and slack first.

[Mfoxchicago]

Thanks Mike, good stuff. I'll be poking around on her this week now that I'm armed with a bit of "what to look for" data.

You and Fred are great guys and so helpful.

[Mfoxchicago]

Ok, I felt around on the Stuart and seemed to have isolated the knocking noise to be coming from the bottom of the connecting rod attached between the eccentric the valve chest piston. When actuated by hand, the connecting rod makes a noise very much similar in temper to the sound it makes when running up at full speed. I think if I tighten up the connection or have the connecting rod reworked so it fits the slot better, the knocking may be eliminated.

Your thoughts........

[Lopez Mike]

Not quite sure where you are referring to on your engine.

Does the loose connection seem to be part of the valve gear? If so, look carefully where the valve rod fits in the valve itself inside the valve chest. I have several times found that looser than it needs to be. It does need some play so that the valve can seat on the cylinder face but not more than a thou or so.

If it's at the connecting point between the valve rod and the valve connecting rod (needs a better name) then you are probably on the right track.