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Old 04-21-2019, 07:41 PM   #1
mumpsimus
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Default 21 stud motor rebuild, beginner questions

My 1937 motor is leaking badly at the rear main. I think it’s time for new piston rings. Cylinder #1 was low compression, leaking down past the rings and blowing oil out the breather and also into the bellhousing. And I might as well measure everything while I have the motor apart to see if anything else needs attention.

I’ve rebuilt a lot of 1910-1940 motorcycle motors, but never a V8. I have a few questions.

1. What book or manual is recommended (listing acceptable wear amounts, etc)?
2. Is there a preferred rear main seal or modification for a 21 stud motor?
3. I was planning to call Hastings for rings, but I’m open to other suggestions.
4. I might install a mild cam for more mid range torque, any recommendations?
5. Can the clutch be cleaned, or is it ruined?
6. Any other suggestions while I take the motor apart?

Thanks in advance guys! I enjoy learning about my Ford, but I wish that I could have kept the motor in it a while longer.

Regards,
Pete
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Old 04-21-2019, 07:58 PM   #2
drolston
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Default Re: 21 stud motor rebuild, beginner questions

Schneider 248f cam is very strong in the mid rpm range, and very drivable in traffic.
If the clutch has oil on it, it should be replaced.
In taking the engine apart, take lots of pictures.
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Old 04-21-2019, 08:55 PM   #3
cas3
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Default Re: 21 stud motor rebuild, beginner questions

if you've never been to mac vp's web site, thats a good start for education and parts http://www.vanpeltsales.com/ lots of info there and mac is a great guy for questions
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Old 04-22-2019, 06:05 AM   #4
Ggmac
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Default Re: 21 stud motor rebuild, beginner questions

No rear main seal , it uses a slinger. If it hasn't run in a while I'd soak the rings down with MMO then run a few cycles to heat and cool the parts . Then recheck the compression .
Ol Rons book is good .
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Old 04-22-2019, 09:13 AM   #5
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Default Re: 21 stud motor rebuild, beginner questions

Oil level can also be an issue in these engines, overfilling them leads to more oil getting past the rear slinger. There is some information on Red's site: http://www.reds-headers.com/html/red...e_talk_24.html

Last edited by JSeery; 04-22-2019 at 09:31 AM.
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Old 04-22-2019, 12:42 PM   #6
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Default Re: 21 stud motor rebuild, beginner questions

Thank you! That page on Red's site describes it well. And I might have been overfilling the oil. I did a four-hour freeway drive and the motor leaked about 1 quart every 75 miles. Ugh. It doesn't leak for drives around town, but the sustained high-speed driving really made a mess.

I'm afraid that I need to pull the motor anyway to fix the rings on the #1 cylinder (and to replace the clutch). If I don't change those rings, it seems that the motor will forever be puking oil onto the clutch.



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Oil level can also be an issue in these engines, overfilling them leads to more oil getting past the rear slinger. There is some information on Red's site: http://www.reds-headers.com/html/red...e_talk_24.html
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Old 04-22-2019, 01:01 PM   #7
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Default Re: 21 stud motor rebuild, beginner questions

A couple of flathead tools will help you during the teardown. A flathead valve spring compressing/guide bar, and a keeper removing tool will go a long way in lowering the number of curse words you will use if you try to remove the valves without them.
Good luck.
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Old 04-22-2019, 01:56 PM   #8
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Default Re: 21 stud motor rebuild, beginner questions

VanPelt rents some of the tools if this is a one time deal. Otherwise it is a good investment to have the proper tools on hand.
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Old 04-22-2019, 10:01 PM   #9
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Default Re: 21 stud motor rebuild, beginner questions

Another nice thing about a 37 motor is cam bearings and insert bearings. If you are installing a new cam a linebore is not out of question. But if you are doing that a full rebuild is okay. Not to take you out of service for the summer.


or just run it till it doesn't. If you have power and it doesn't overheat. Oil is cheap.

Last edited by Tinker; 04-23-2019 at 01:38 AM. Reason: miss type... I'm getting older I guess
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Old 04-22-2019, 10:20 PM   #10
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Default Re: 21 stud motor rebuild, beginner questions

I think 'barnfind08' , a member on here, stocks NOS rear main bearing drain pipe. Get one off of him and fit it to the rear main, there is provision for it. What this does is allows oil to return from the slinger setup back into the engine. Without this tube screwed into the hole, crankcase windage can blow through the hole, and out past the labyrinth, taking oil with it, resulting in the big slick you're seeing under your car.
Alternatively, Reds Headers sells a positive rear seal conversion, which is a bit more involved, including grinding off the second slinger on the crankshaft.
You asked for tips....
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Old 04-23-2019, 12:32 AM   #11
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Default Re: 21 stud motor rebuild, beginner questions

Id like to just run it, but the clutch is slipping really badly

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Another nice thing about a 37 motor is cam bearings and insert cam bearings. If you are installing a new cam a linebore is not out of question. But if you are doing that a full rebuild is okay. Not to take you out of service for the summer.


or just run it till it doesn't. If you have power and it doesn't overheat. Oil is cheap.
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Old 04-23-2019, 12:36 AM   #12
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Default Re: 21 stud motor rebuild, beginner questions

Thanks! Thats good info. Im not sure what it take to pull out the whole crank. I guess all the rods, mains, plus timing gear. A real seal sounds like a good improvement though. Ill locate barnfind08 and ask his opinion on the labyrinth vs positive seal.

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Originally Posted by Brian View Post
I think 'barnfind08' , a member on here, stocks NOS rear main bearing drain pipe. Get one off of him and fit it to the rear main, there is provision for it. What this does is allows oil to return from the slinger setup back into the engine. Without this tube screwed into the hole, crankcase windage can blow through the hole, and out past the labyrinth, taking oil with it, resulting in the big slick you're seeing under your car.
Alternatively, Reds Headers sells a positive rear seal conversion, which is a bit more involved, including grinding off the second slinger on the crankshaft.
You asked for tips....
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Old 04-23-2019, 12:57 AM   #13
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Default Re: 21 stud motor rebuild, beginner questions

No need to pull the crank to fit the tube, only to fit Reds conversion. Generally, these old 21 studs will leak more as the rear main bearing [and others], but mainly the rear main [no pun intended], wears.
If you just want to freshen it up without spending lots of money, you can replace the rear main bearing with crank in place, but fit that tube at same time and you'll really notice a change in leakage. These are cool old motors and you'll be amazed at their longevity. And I like your woodie. Obviously, do a clutch job at same time.
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Old 04-23-2019, 01:17 AM   #14
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Default Re: 21 stud motor rebuild, beginner questions

You see...what happens is that #1 cylinder you mention, [but probably others too], has low compression. Because of your ring issue that compression leakage is going straight into the crankcase [windage]. This means the crankcase is getting pressurised. This pressure needs to vent outside to atmosphere, and will take any and all paths possible in order to do so....
The rear main bearing cap has a hole in it to allow oil to return to the sump. As there is no positive seal in the back of these motors, and as the rear main clearances have increased somewhat larger than from when new, this provides an excellent escape route to vent some of the windage. And escape it will, straight into the clutch housing, taking with it a nice oily mist....
Now, when you fit the tube, [which interestingly, was used in early production, and dropped in 35], the oil can return from the rear main, but runs into and under the level of oil held within the pan. Which conveniently also stops the pressurised crankcase fumes from escaping via that route.
Hope this makes sense, it is my opinion only, arrived at after years of playing with 21 stud engines.
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Old 04-23-2019, 11:07 AM   #15
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Default Re: 21 stud motor rebuild, beginner questions

That is my understanding too Brian. (but I didn't know about the tube). The car sat for about 20 years after a rebuild. I bought it two years ago and have done 2500 miles, but with a constant spray of oil from the breather, and occasional oil from the bellhousing. Compression is about 90psi on all cylinders, except #1 is 55psi. I've been trying to avoid pulling the motor, but I guess I have to now. I'll try that tube at the rear main solution. It sounds perfect.


Quote:
Originally Posted by Brian View Post
You see...what happens is that #1 cylinder you mention, [but probably others too], has low compression. Because of your ring issue that compression leakage is going straight into the crankcase [windage]. This means the crankcase is getting pressurised. This pressure needs to vent outside to atmosphere, and will take any and all paths possible in order to do so....
The rear main bearing cap has a hole in it to allow oil to return to the sump. As there is no positive seal in the back of these motors, and as the rear main clearances have increased somewhat larger than from when new, this provides an excellent escape route to vent some of the windage. And escape it will, straight into the clutch housing, taking with it a nice oily mist....
Now, when you fit the tube, [which interestingly, was used in early production, and dropped in 35], the oil can return from the rear main, but runs into and under the level of oil held within the pan. Which conveniently also stops the pressurised crankcase fumes from escaping via that route.
Hope this makes sense, it is my opinion only, arrived at after years of playing with 21 stud engines.
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Old 04-24-2019, 09:19 AM   #16
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Default Re: 21 stud motor rebuild, beginner questions

Don't know how far you want to go with rear oil leak or if Red's headers even sells the kit any more but the link below shows pictures of what we did on my 35 21 Stud. Dave/Green Bay

https://www.fordbarn.com/forum/showthread.php?t=21404
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