H70 blows a little smoke after rebuild

[Mailman]

Hey guys,

I rebuilt an H70 recently. It blows a little white smoke in the higher rpms. Do I just need to give it a little time to break in the new rings?

I honed the cylinder and put in a fresh aftermarket piston kit that I got off Ebay. I don't remember if it had chrome rings or not.

The valves are new and the valve seats were cut so all that should be good.

 

[Briggsboss]

check the valve lash (gap)? new valves still need to be set
just in case great download; page 85
http://www.imarksweb.net/book/3+10+hp+4+cycle+tecumseh/

Hey guys,

I rebuilt an H70 recently. It blows a little white smoke in the higher rpms. Do I just need to give it a little time to break in the new rings?

I honed the cylinder and put in a fresh aftermarket piston kit that I got off Ebay. I don't remember if it had chrome rings or not.

The valves are new and the valve seats were cut so all that should be good.

 

[mc73cromags]

Probably the rings just need to seat. Unless the valve guide clearance is huge, it is unlikey that it will suck excessive amounts of oil through the valve guides in a horizontal shaft flat head engine. When you installed the rings did you offset or stagger the ring end gaps? If the ring end gaps are lined it is possible you could get a little oil past the rings

 

[Mailman]

Probably the rings just need to seat. Unless the valve guide clearance is huge, it is unlikey that it will suck excessive amounts of oil through the valve guides in a horizontal shaft flat head engine. When you installed the rings did you offset or stagger the ring end gaps? If the ring end gaps are lined it is possible you could get a little oil past the rings

Yes, I did offset the ring gaps. Thanks for the idea though. Hopefully the rings will seat after break in.

How do you guys usually break in your motors?

 

[metalhead100]

did you clean out the breather and or make sure the crankcase is vented.....it could cause it to pump oil into the bore .....if its clogged.........

On the other hand if its puffing out the breather hard its blow by from the rings not sealing.........

 

[Mailman]

check the valve lash (gap)? new valves still need to be set
just in case great download; page 85
Download: 3 10 hp 4 cycle tecumseh at Marks Web of Books and Manuals

I did set the valve clearance

did you clean out the breather and or make sure the crankcase is vented.....it could cause it to pump oil into the bore .....if its clogged.........

On the other hand if its puffing out the breather hard its blow by from the rings not sealing.........

I did clean out the breather really well but I could check that again.
Thank you.

 

[MB165]

Did you measure the bore and compare it to specs?

 

[Mailman]

Did you measure the bore and compare it to specs?

Yes, I forgot what it was but it was within specs.

 

[TomH]

Do a light test on the head. Take the head off and shine a bright light on the head and look into the ports with the valves in place. If you see any light, you don't have a good seal with your valves and seats.

 

[Mailman]

Do a light test on the head. Take the head off and shine a bright light on the head and look into the ports with the valves in place. If you see any light, you don't have a good seal with your valves and seats.

With new valves and having the seats cut by a shop, I don't see how the valves could be leaking. I am new to this so correct me if I am wrong. I also adjusted the valves to spec.

I did run the motor for 10 minutes or so and the amount of smoke went down considerably. Is this due to rings starting to seat or just the hot motor parts making the rings and piston seal better?

I appreciate all the help guys. I will run it for another 10 mins or so and see if the smoke is still there and report back.

 

[TomH]

The shop isn't perfect. Just because you paid someone else to do it, doesn't mean they did it right I am sorry to say. But I would bet that is your problem. Let me find this video for you. Check this out below. The head was sent out for machine work.
HOW TO Check Valves for Proper Seating on OHV Engines - YouTube

You can do the same thing with a flat head type engine

 

[Mailman]

I ran it for another 15 to 20 minutes and the amount of oil decreased but it is still blowing some.
Should I just bore it and put in an over sized piston? That way I know it is in spec.

 

[Mailman]

The shop isn't perfect. Just because you paid someone else to do it, doesn't mean they did it right I am sorry to say. But I would bet that is your problem. Let me find this video for you. Check this out below. The head was sent out for machine work.



Thanks Tom. I did fill the vavle area with carb cleaner and turn the engine up side down to check for leaks and it passed. Most of the used engines I do that to leak some liquid. I saw this in the Tecumseh manual.
Even if the valves were leaking a little, would it really cause it to blow a bunch of smoke while it is running?

I am going to pull the head either way but I suspect the bore is not in spec. In hindsight, I may not have checked the bore in enough spots. I will tear it down and check it again along with the valves. Is the "light test" better than the fluid leak test Tom?

 

[TomH]

The shop isn't perfect. Just because you paid someone else to do it, doesn't mean they did it right I am sorry to say. But I would bet that is your problem. Let me find this video for you. Check this out below. The head was sent out for machine work.



Thanks Tom. I did fill the vavle area with carb cleaner and turn the engine up side down to check for leaks and it passed. Most of the used engines I do that to leak some liquid. I saw this in the Tecumseh manual.
Even if the valves were leaking a little, would it really cause it to blow a bunch of smoke while it is running?

I am going to pull the head either way but I suspect the bore is not in spec. In hindsight, I may not have checked the bore in enough spots. I will tear it down and check it again along with the valves. Is the "light test" better than the fluid leak test Tom?

Yeah sure is. They might lap in. Other blow by problem is if you put your 3 rings where the gap is in the same spot. The ends of the rings need to be 120 degrees from each other. One of them could be broken or cracked, or you could have a worn out cylinder which I doubt. I bet you check your valves you will see a bit of light shining in there.

 

[Mailman]

I tore it down and the valves were perfect. It turns out that the cylinder was worn. I ordered a .010 over piston and rings for it.
Any advice for break in?

 

[TomH]

You will probably get plenty. Everybody has a different way it seems. I like to let it idle until it gets all the temps up, usually adjusting the carb. Get on it and ride it. I run it steady throttle and then goose it to force the rings to seal. I don't wind it real high, just slow down and goose it up for 10 12 times. Rap it up a bit, play with it, slowing down speeding up 15 20 minutes. Change the oil as soon as I stop to keep all the little particles suspended. Pour the new oil in and from there I drive it anyway I want. I check the oil and when it starts to get dirty, change it again. that is pretty much it.

 

[Mailman]

Thanks Tom. That makes a lot of sense.
By the way; Do you install the rings and cylinder dry or do you put oil on them?
I have read that if you oil them then they will always let oil by and a dry install is the best way to go.

 

[TomH]

I have used oil and not. If you have a crappy ring compressor like I had, oil was one of the desperation movies I tried to get them into the top of the cylinder. Cussing didn't seem to help.:laugh:

 

[Mailman]

OK. Thanks.
I will try it dry this time and change the oil often. I will post back up when it is back together and let you know how it turns out.

 

[Mailman]

The bore was just worn out. I put a .010 over piston in it and had it bored and honed. It runs great and doesn't smoke.
It feels good to be done with this monster. Thanks for your help.