Valve Noise


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Old 06-13-18, 05:42 PM
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Valve Noise

I've owned a Craftsman with an opposed twin 400707 type 0126 for 31 years. It's my baby which I have took very good care of. It runs great, like a top as it always has however, this year I've noticed an increase in valve ticking than usual. I'm thinking it's time to pull the heads and check the tappet to valve stem clearances however, I want to check here for any input someone may have to offer before I proceed. Would no tappet to valve clearance cause more valve noise? Thanks in advance for the replies.
 
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Old 06-13-18, 06:00 PM
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These engines don't get valve noise really. You're probably hearing something else. These engines actually get less clearance between the valve stem and tappet as they wear, not more. No tappet clearance would not allow any tapping, so it would cause less noise. With the tappet-to-valve contact area being down in the block instead of up top like an OHV engine, valve noise can barely be heard if at all. I'd suspect piston slap or wrist pins or something like that if it's a lighter sound. You can't check the clearances by pulling the heads.
 
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Old 06-14-18, 09:54 AM
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Cheese, thank you very much for your reply. You confirm what I was thinking. Yes, it is light tapping but at a higher frequency than the crank rotation so I don't think it's rod bearings, no knock at all. I was going to pull the heads so I could remove the valves of course, i was going to check tappet to valve stem clearance first. Shouldn't I be able to confirm play in the wrist pin by removing the head and slowly rotating the crank and observing play? It seems I've got a rebuild on my hands. I will assume I would need to replace pistons and connecting rods? I've done a rebuild on a different engine some years ago and have the cylinder hone to get the cross hatch for new rings.
 
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Old 06-14-18, 11:42 AM
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Well, without being there to hear it, I can't say if you need a rebuild or not but if it's not smoking and it's not a rod knock, I'd say let it be. Wrist pin and piston slap cause noise but rarely failure. You can detect some play by checking the way you described but I don't know how you would know if it was wrist pin or rod play. Both will allow some delay in piston movement. Usually the top rod is the noisemaker in these engines because it is farthest from the oil sump. If the noise is bad enough to investigate, then I'd pull the head for the top cylinder and check for slack between the piston and crank. If there is any, it's most likely going to be a connecting rod and in that case, I'd look into a rebuild if the mower is worth the effort.
 
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Old 06-14-18, 03:22 PM
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Makes perfect sense Cheese. It doesn't smoke at all and has plenty of power. I went out today and rotated the crank by hand. Just as you described, the tapping is close to the top of the engine right beneath the fly wheel. I'm now suspecting a top rod bearing even though it sounds like more of a tinky sound than a knock. After 31 years of service I couldn't expect anything more out of the old girl. It's been one hell of an engine in fact so good, I'm going tare it down and install new piston,rods and rings. I'll check the valves while I'm in but I think there fine due to how good it runs. Any advice on the rebuild or recommendations on valve lapping or leave as is would be most appreciated.
 
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Old 06-14-18, 09:12 PM
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Check for scoring on the rod journals on the crank, check for a ridge on the cylinders. If there is much of either, I'd get them checked to make sure they are within specs unless you have a micrometer, then do it yourself. If no scoring and little to no ridge, chances are it will be fine. Use a good assembly lube, cut the glaze on the cylinders and get a good crosshatch pattern, make sure the ring end gaps look good all the way down the cylinders, and put er together. Check the valve clearances. If they are close to spec, I'd leave them. If not, grind the stem to obtain proper clearance. If the valves look good on inspection and the seating area isn't heavily worn, I wouldn't lap them. If they are stained in the seating area instead of bright, maybe lap if the surfaces aren't too worn. If the seating surfaces are pretty worn, a regrind may be in order.
 
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Old 06-15-18, 11:39 AM
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Cheese, Thanks so very much for sharing your experience. It is greatly appreciated!
 
 

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