Carbon build up on exhaust valve. - Snowblower Forum : Snow Blower Forums
 
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post #1 of 8 Old 11-17-2015, 08:55 PM Thread Starter
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Carbon build up on exhaust valve.

Hi all, been reading on forum a lot but had a question to ask advice.

Recently got an ariens with a h70-130067a on it. New carb and points and condenser got it running and I was very happy with myself.

Started it again next day to adjust carb etc and pop, head gasket went.... Took head off and confirmed. This leads to my question.

The head was very clean with little to no carbon build up, but the exhaust valve was very black. Wondering if this indicates any issues or is common?

Any advice on replacing head gasket?

Thanks in advance for any replies.
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post #2 of 8 Old 11-18-2015, 07:26 AM
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The soot by itself is a little hard to comment on. The question (which will be hard to answer at this point) is are there other symptoms like smoke when it's running. Then you'd be looking at piston/cylinder/ring wear or possibly valve guides.

A quick funny story: when I was young, I had a Tecumseh 6 HP engine that I used on several snowblowers as well as a few go-karts and minibikes (that engine worked for a living!). In general it ran perfectly, and did not smoke at all. One day it absolutely refused to start, and after trying everything I pulled the head and found the top of the piston and valves covered with wet soot. I cleaned them up with a paint scraper, put the engine back together, and it started on the first pull and ran fine for years afterward! I never did find the cause of the soot, nor was it ever again a problem.

Re the head gasket... there are really no "tricks" except to try to get an idea why it might have failed. In general, they don't "just do that". Were the head bolts all tight? If not, can they be made tight, or are the holes stripped?

Also when you replaced the points, are you sure you set the gap correctly? Improper gap could alter the timing which could (in an extreme case) cause head gasket failure.

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Last edited by ELaw; 11-18-2015 at 07:28 AM.
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post #3 of 8 Old 11-18-2015, 09:21 AM
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The exhaust valves are usually pretty black, so that's normal. When doing a head gasket on one, I'll remove the small rectangular cover on the side of the engine, pop the valve keeper off the top of the spring, and run the valves on a wire wheel with a fine bristle.

As long as the valves were seating right, my guess is that the head bolts weren't tight enough. Remember to go in a star pattern when you do it.
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post #4 of 8 Old 11-18-2015, 04:30 PM Thread Starter
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Thanks for replies.

It was first time I had done points, like everything else I'm learning. So I think I did them correctly.

I got a torque wrench so will look to set bolts correctly. I'll be able to answer smoke when running question this weekend all going to plan....

Should I put on a sealant when putting in new head gasket?
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post #5 of 8 Old 11-19-2015, 08:49 PM
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Nope, just stick it on dry. The original head gaskets are a perforated metal gasket that crush when torqued, the new ones are graphite.
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post #6 of 8 Old 11-22-2015, 11:31 PM Thread Starter
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So while replacing the head gasket I realised why it failed. As suggested bolts not set correctly.

When I replaced the points and condenser I had to remove the flywheel and obviously the cover from the flywheel. Being a novice and not owning a torque wrench I didn't realise that 3 of the bolts I had to take off were for the head. When I replaced the cover I didn't tighten then correctly.

I replaced the head gasket tonight, after purchasing a torque wrench.
Followed the sequence in the manual for bolts and set them to 17ft lbs. Manual says a range in inch lbs. I took midpoint of 200 and hopefully converted it correctly.

Thanks for all the input.
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post #7 of 8 Old 11-24-2015, 09:12 AM
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Quote:
Originally Posted by Nconroy1 View Post
So while replacing the head gasket I realised why it failed. As suggested bolts not set correctly.

When I replaced the points and condenser I had to remove the flywheel and obviously the cover from the flywheel. Being a novice and not owning a torque wrench I didn't realise that 3 of the bolts I had to take off were for the head. When I replaced the cover I didn't tighten then correctly.

I replaced the head gasket tonight, after purchasing a torque wrench.
Followed the sequence in the manual for bolts and set them to 17ft lbs. Manual says a range in inch lbs. I took midpoint of 200 and hopefully converted it correctly.

Thanks for all the input.
In/lbs divide by 12 = ft/lb. You got it about right. Might want to retorque after a few hours running time.

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post #8 of 8 Old 12-03-2015, 11:50 PM Thread Starter
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So I've got everything back together and re torqued after running for a while.

I can't get the engine to run smooth, it runs and starts up easily just sputters and there is a little smoke coming from the exhaust every now and then. I've never been shown how to adjust carb but have learnt a lot through research etc... I've got my 1964 running smoothly.

I'm concerned its the points... Would a Nova 11 work on the machine? are these a good investment? do you think the sputter may be from the timing due to the points being gapped incorrectly?
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