1975 Cub valves

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Glen
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Re: 1975 Cub valves

Postby Glen » Tue Aug 28, 2018 4:20 pm

Hi,
Below is a page from the Cub service manual showing the timing marks.

Align mark number 1 in the pic with the pointer, using a timing light, when the engine is running at low idle speed, 500 RPM.
As you speed up the engine, the timing should advance partially up to mark number 2, and be about at mark 2 when running at high speed, 2000 RPM.
Maybe you knew this already.
They are talking about other subjects on the page. :)

http://www.farmallcub.info/manuals/gss- ... 001-43.jpg

Jamesk
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Re: 1975 Cub valves

Postby Jamesk » Tue Aug 28, 2018 8:20 pm

So this afternoon I ran the cub about an hour and a half. It seems to be a valve problem. Two different times a valve started tapping and the engine lugged. I cut the engine off the first time. The oil pressure was 25 lbs 1/2 to 3/4 throttle. I let the engine set for maybe two minutes and started it back up. There was no valve tapping. I drove it back home and made laps in the yard til it started tapping again. This time I was at full throttle and 30 lbs oil pressure. I lowered the throttle and the engine slowly came to a fault. One minute later I cranked it again and there was no valve tap. Made another lap around the yard and parked it. I got the second time on video and intend to send to the rebuilder in the morning. This is crazy.

Jk

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Glen
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Re: 1975 Cub valves

Postby Glen » Tue Aug 28, 2018 10:43 pm

Hi,
Too bad that is happening.
It sounds like one or more valves are sticking open as the engine warms up, and the metal expands.
When you stop the engine, it eventually closes again.

Also, the valve springs have to be good, and not weak, so they pull the valves closed correctly.
You didn't say if they replaced the valves, valve guides, or valve springs.

Below are pages from the Cub service manual showing the valve clearance, valve guide ID's, and info for the valve spring testing.

http://www.farmallcub.info/manuals/gss- ... 001-07.jpg

http://www.farmallcub.info/manuals/gss- ... 001-08.jpg

Below is the whole Cub service manual. The engine is in section 1, it has pages showing the valves.

http://farmallcub.com/rudi_cub/www.clea ... index.html

It might improve if you keep using it, and wear enough to work right, but I can't tell without being there.

Jamesk
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Re: 1975 Cub valves

Postby Jamesk » Tue Aug 28, 2018 11:22 pm

I was supposed to have gotten a complete overhaul. New valves valve guide springs every thing new. We’ll find out tomorrow morning

Jk

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Re: 1975 Cub valves

Postby Scrivet » Wed Aug 29, 2018 7:39 am

Jamesk wrote:..... I let the engine set for maybe two minutes and started it back up. There was no valve tapping. ............. I lowered the throttle and the engine slowly came to a fault. One minute later I cranked it again and there was no valve tap. ..............
I'm no valve expert but to my thinking one or two minutes is not near long enough for that hunk of cast iron that's an engine block to cool enough to make a difference. Especially since it took
Jamesk wrote:....... I drove it back home and made laps in the yard til it started tapping again. This time I was at full throttle and 30 lbs oil pressure. ............
to get it hot again to recreate the problem.

I'm not saying it's not valve related, just not to focus so hard on it being a valve problem that you're missing something else.

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Shane Nelson
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Re: 1975 Cub valves

Postby Shane Nelson » Wed Aug 29, 2018 7:59 am

I agree with Scrivet, I'm thinking bearing related, not valve train related. Let us know what you find out.
Every home is a school, what are you teaching?
Circle of Safety

Jamesk
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Re: 1975 Cub valves

Postby Jamesk » Wed Aug 29, 2018 2:56 pm

I will let everyone know when we get it figured out. I call the rebuilder again this morning and asked if he put new valve springs in at over haul. He said he couldn't remember but that he personally put the valves and valve guides in the motor. So the way I see it, he knows if he put new springs in or not. I do agree with you guys about the possibility of there being a bearing problem and that a minute or two just doesn't seem to be long enough for the engine to cool down. I took a video of the motor last night right at dark, the second time it did it. It actually killed the engine.
I can send a link if anyone wants to listen to this thing. I will need an email address. PM me with your email address and I'll send the link.

The rebuilder said to go ahead and run the tractor with the marvel oil in the gas, that this will not hurt the engine. The only problem I have with that statement is that he hasn't heard what I've heard. He also said that he would make it right either way that he would drive to my house and listen to the motor if it doesn't settle down. So I'm gonna run it through the weekend and see if it stops.

Sure wish a couple of you guys would listen to this thing, sounds terrible.

JK

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AL Farmall Boy
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Re: 1975 Cub valves

Postby AL Farmall Boy » Wed Aug 29, 2018 3:37 pm

James......pull the spark plugs to see if the ends of the electrodes have been hit by a piston. That will make the engine die, make a rattle/knock noise, and also mean that there is a bearing problem. I am dealing with that on a Polaris RZR 900 right now. For the RZR, I am thinking it will be best to sell it as a project for someone. You thought Cubs were expensive to rebuild.......try $3,500.00 just for a new engine for the RZR!

Send me the link. Email is below.
Regards,
Chase
205-368-5339
ihfarmallrtr@gmail.com

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Jamesk
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Re: 1975 Cub valves

Postby Jamesk » Wed Aug 29, 2018 3:51 pm

Hello Chase, I'm sure I'll eventually get this thing right but its getting under my skin in the tender spots if you know what I mean.
I will check the plugs but I don't think that's the problem because it runs really well up until it starts making the tapping noise. If the pistons are touching the plugs it would have to be minimal for it to keep running. Oh yea, I don't need an RZR for sure.

JK

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Glen
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Re: 1975 Cub valves

Postby Glen » Wed Aug 29, 2018 4:50 pm

Hi,
I agree with the guys above, the valves are not the only thing that the problem could be, it seemed likely to me because it ran normally again after sitting.

Scrivet, the engine may not have cooled hardly at all when he stops it for a few minutes, but it is possible that the valve spring closes the valve when it is stopped.
It sounds like the valve is just to the point of fit in the guide where it works tightly, and the spring cannot always close it, but does close it most of the time.

I may be wrong, and it is something else.

You may need to check it out by removing the valve cover and looking to see if a valve sticks open.
I don't know if you want to, the cover is sort of hard to get off the engine. If you run it with the cover off, some oil is probably going to squirt, or run out and make a mess. I don't know if you have new paint. :)

Jamesk
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Re: 1975 Cub valves

Postby Jamesk » Wed Aug 29, 2018 8:49 pm

Its painted.

JK
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AL Farmall Boy
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Re: 1975 Cub valves

Postby AL Farmall Boy » Thu Aug 30, 2018 2:59 pm

It wouldn't hurt to run it with the cover off so you can see what is going on. The oil should clean up fine and use some deagreaser with a power washer once all back together to get it cleaned out of hard to reach areas.
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AL Farmall Boy
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Re: 1975 Cub valves

Postby AL Farmall Boy » Tue Sep 04, 2018 8:06 am

Just curious what came of this?
Regards,
Chase
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Jamesk
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Re: 1975 Cub valves

Postby Jamesk » Wed Sep 05, 2018 12:59 pm

Hi Chase,

I went to the rebuilders shop last Thursday, kinda showed up unexpected. He is supposed to come to my house (about a 40 mile trip for him) to listen to the motor. He assured me that he would take care of the problem. He said that he would have to find the time to get away from the shop. So far I have not heard from him. I'm waiting on him to call and make a visit.

JK

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AL Farmall Boy
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Re: 1975 Cub valves

Postby AL Farmall Boy » Fri Sep 07, 2018 8:11 am

Ok. Didn't know if anything changed since then. Keep us updated.
Regards,
Chase
205-368-5339
ihfarmallrtr@gmail.com

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