Model N Engine rebuild

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bobster1
Posts: 57
Joined: Sun Sep 24, 2017 6:33 pm
Location: Richmond, VA

Model N Engine rebuild

Post by bobster1 » Sat Dec 01, 2018 2:11 pm

OK Folks, I've pulled my Model N (07') down for inspection and rebuilding as necessary. Any words of wisdom??? So far I've found compression to be 45-30-50-50 PSI, not sure what it would have been originally? I found one burn valve and one spark plug/jug plug with a bad thread that would explain the low compression. I also found excessive valve clearances .030 to .036, another explanation for low compression. The cam appears to be reground and I have a new Stipe cam for replacement. I did find the cam gear rubbing the back of the crankcase due to too much front to back movement, .033. Tappets must be new replacements as no wear, however someone re-ground each one to a different length, I assume to adjust valve clearances. The tappet guides are like new with no wear. I will need to replace the valves as they will all be to short unless the regrinding of the seats takes up the excessive clearance? Does anyone know a source for valves, tappets or the valve springs? I notice in the parts book they list different valve springs for intake and exhaust, anyone have additional info on this, my springs are all different so not sure what's right or wrong.Any help is appreciated!

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ddunlavy
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Location: Decorah IA USA
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Re: Model N Engine rebuild

Post by ddunlavy » Sat Dec 01, 2018 9:28 pm

Quick reply. Check with Richard Darling for valve springs. He has some made. Call me if you can't find Tele nr.
Not sure if he does much computer.
Of course if you are going to replace cam everything above that must be measured and set after you regrind valves.
Keep us posted.
Also Merry Christmas.
Dave

bobster1
Posts: 57
Joined: Sun Sep 24, 2017 6:33 pm
Location: Richmond, VA

Re: Model N Engine rebuild

Post by bobster1 » Sun Dec 02, 2018 12:52 pm

Thanks Dave, I give him a call on the springs. I understand the setup for valve clearances, I can see that it would be nice to install new valve seats in the head. I wonder how much meat is in the jug heads for cutting in a modern seat? I do have a spare head to experiment on, but has anybody had any experience in this area???? Thanks Bob

JVanMaanen
Posts: 45
Joined: Sat Jun 20, 2015 2:35 pm

Re: Model N Engine rebuild

Post by JVanMaanen » Thu Dec 13, 2018 11:12 pm

Bob:

Floyd Jaehnert had new correct valve spring sets. Not sure if he still does. For valves I used melling V0658 valves. The heads are 1.5" diameter, 45 degree seat and a stem diameter of 0.372 which is close to the orginal 0374 NRS. They are 5.736" long so you need to cut them to length once you know what that length needs to be and drill them out for the spring keepers. If you go to melling.com and do a parts lookup, you can specify criteria for a part and search for a match. Once you find a match for your valve specs the challenge can be to find vender who has them or is willing to order them for you. Melling is the manufacturer so last time I checked they only sell in quantity.

Jim

bobster1
Posts: 57
Joined: Sun Sep 24, 2017 6:33 pm
Location: Richmond, VA

Re: Model N Engine rebuild

Post by bobster1 » Fri Dec 14, 2018 9:45 am

Jim, thanks for the info! I do have some valve springs coming from Floyd, however they are more spring pressure than factory spec. I'm going to measure them before I use them in the engine. I also have several spare Jug Heads, one of which is scrap, but great for experimenting. I'm going to do some test machining to see if there's enough meat to install hardened valve seats. I hope when I'm done to be able to compile a list of replacements parts I use for the rebuilding of this engine. Thanks again for your comments!

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