Impact to Cylinder Head Cover While Running - Backfired to a halt, now won't start

[NathanF]

That was a pretty decient whack you gave it there.
Should not be any problems with the engine as the dent would have been pushing the valves open against the valve spring.
Just have a close look to make sure the retaining collars on the valves have not popped off which is the only problem you are likely to have on the rocker box side.
On the other side there is a possability that the piston have have touched the valve head(s) and bent one of them.
This will be hard to diagnose without pulling the head off. The usual indication is that one or both of the valve clearences will be a lot bigger than it should be.
But as you say the valve lash is still withing specs you may have lucked this one in.
Start the engine without the valve cover on and watch the operation of the valves, if they are nice & regular pop a new cover on , refill the oil and go mow.

Thanks for all the advice! The springs, retaining collars, etc.. all look good visually, as near as I my novice eye could tell. To clarify one thing, I don't have a feeler gauge (ordered one on Amazon, coming in a few days) so I was just visually looking things. A few minutes ago I beat the old cover back into shape and reinstalled it to keep oil from going everywhere, then started it up as per your suggestion. It started and ran perfectly, at least as far as I could hear. Very reassuring! I'll run it again tomorrow outside with the cover off and observe the valves. Maybe I'll put the slow-mo video feature of my phone to use! :wink:

Do you think I should replace the exhaust side arm? It looks weird to me that the exhaust valve bolt head is offset a few mm down from being center with where it contacts the valve stem. If I push the arm up slightly it seems to be centered, but the intake / right side is dead on center without such fiddling. For all I know that is normal, but I'm wondering if maybe the arm got slightly tweaked. I placed an order for a new aluminum cover, gasket, bolts, and the arm assembly since it was only $4 USD. I'll install it and see if that fixes the centering issue. If so, I'll adjust the valve to spec and hope for the best.

If it doesn't fix the centering issue, then I guess that would lend evidence to the valve stem being bent. Like I said earlier though, I used my calipers to measure the distance of each valve stem to the top of the block and they seemed identical. I'm hoping that just means the arm or adjustment bolt is slightly tweaked rather than the valve stem.

 

[bertsmobile1]

Thanks for all the advice! The springs, retaining collars, etc.. all look good visually, as near as I my novice eye could tell. To clarify one thing, I don't have a feeler gauge (ordered one on Amazon, coming in a few days) so I was just visually looking things. A few minutes ago I beat the old cover back into shape and reinstalled it to keep oil from going everywhere, then started it up as per your suggestion. It started and ran perfectly, at least as far as I could hear. Very reassuring! I'll run it again tomorrow outside with the cover off and observe the valves. Maybe I'll put the slow-mo video feature of my phone to use! :wink:

Do you think I should replace the exhaust side arm? It looks weird to me that the exhaust valve bolt head is offset a few mm down from being center with where it contacts the valve stem. If I push the arm up slightly it seems to be centered, but the intake / right side is dead on center without such fiddling. For all I know that is normal, but I'm wondering if maybe the arm got slightly tweaked. I placed an order for a new aluminum cover, gasket, bolts, and the arm assembly since it was only $4 USD. I'll install it and see if that fixes the centering issue. If so, I'll adjust the valve to spec and hope for the best.

If it doesn't fix the centering issue, then I guess that would lend evidence to the valve stem being bent. Like I said earlier though, I used my calipers to measure the distance of each valve stem to the top of the block and they seemed identical. I'm hoping that just means the arm or adjustment bolt is slightly tweaked rather than the valve stem.

I am not familiar with the particular motor but it is common practice to off set the contact point of the rocker in order to rotate the valve while the engine is running

 

[NathanF]

I am not familiar with the particular motor but it is common practice to off set the contact point of the rocker in order to rotate the valve while the engine is running

Thanks so much for confirming that. My parts came yesterday, and the new rocker arm was equally offset as the original, so I reinstalled the old rocker and am calling it good. I also checked the valve clearance with my new feeler gauge, and both intake and exhaust were just about perfect.

After installing the aluminum cover and gasket with new bolts (90121-952-000) from Honda, I noticed the bolts protruded through the screw mounts, coming out the backside just slightly. I tightened them to factory spec with my torque wrench, so I definitely did not over-tighten them. It doesn't look like it hurt anything, but it did not give me a warm fuzzy feeling. Robert, any thoughts on that? Besides that I'm really liking the sturdy new cover.

Anyway, I gave it fresh oil, then tried starting it a good 10 times without success...until realizing I forgot to reconnect the spark plug I had disconnected for safety reasons. :laughing: Fixed that and it started right up. I mowed my whole lawn without issue. Thanks to everyone for all the help!

 

[robert@honda]

After installing the aluminum cover and gasket with new bolts (90121-952-000) from Honda, I noticed the bolts protruded through the screw mounts, coming out the backside just slightly. I tightened them to factory spec with my torque wrench, so I definitely did not over-tighten them. It doesn't look like it hurt anything, but it did not give me a warm fuzzy feeling. Robert, any thoughts on that?

No issue at all. The longer bolts ensure the thicker cover can be properly secured.

 

[NathanF]

No issue at all. The longer bolts ensure the thicker cover can be properly secured.

I should have phrased my sentence different. By poke out I mean they actually physically broke through the metal that was previously not drilled and tapped all the way through. It doesn't look like anything cracked though, and no leaks, so I'm not super worried about it.

 

[robert@honda]

I should have phrased my sentence different. By poke out I mean they actually physically broke through the metal that was previously not drilled and tapped all the way through. It doesn't look like anything cracked though, and no leaks, so I'm not super worried about it.

Okay, I see what you mean now. I recall other versions of the GCV engine were drilled deeper or all the way through.

 

[Mike77]

Can the 12312-Z2A-000 gasket be used with 12310-Z0J-000 valve cover ? I don't want deal with the Honda Super/crazy glue again and because of the longer bolts breaking through the blind holes I don't want to use the other cover. Also does anyone know why Honda still makes two regular covers , the 12312-Z2A-000 which has a belt guide and the 12311-Z8B-000 which does not (and costs more).

 

[robert@honda]

Can the 12312-Z2A-000 gasket be used with 12310-Z0J-000 valve cover ? I don't want deal with the Honda Super/crazy glue again and because of the longer bolts breaking through the blind holes I don't want to use the other cover. Also does anyone know why Honda still makes two regular covers , the 12312-Z2A-000 which has a belt guide and the 12311-Z8B-000 which does not (and costs more).

You could try the gasket with the thin steel cover, I suppose. If it works and stays dry, great. Otherwise, might have to use the sealant.

The cover with the timing belt guide is mostly used on horizontal-shaft engines (snow blowers, generators) and helps retain the belt on the camshaft in colder operating conditions.

The cover with OUT the guide is for vertical-shaft engines (lawn mower)

Part prices vary more often due to supplier changes, parts volume, engineering changes, etc. Just because there's a bit less metal used won't absolute force the cost to be lower.