Getting a spark to fit heads

Are ya having a problem with your rig? We'll try to help. Share your tech tips and experiences here. Dr. Billy Glaser, author of the "Unofficial 750 Ural Service Manual" site myural.com, is moderating this section.
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Claus
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Re: Getting a spark to fit heads

Post by Claus » Thu Nov 14, 2019 5:28 am

I don´t see a reason for putting washers under the plugs. There were two different types of plugs used for Dnepr. Long and short thread. Why not use the matching plugs for each head? Talking about NGK that would be BP7HS for the short one and BP7ES for the long one. (or any other make that is obtainable, like Champion RA6HC for the short and R6 for the long ones)
owned bikes: 93 Ural rig domestic model, 95 Suzuki DR 659 RSE, BMW R100GS, Suzuki GSX1100G rig, BMW R100R rig with Ural sidecar, Ural rig with BMW drivetrain under construction,

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Snakeoil
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Re: Getting a spark to fit heads

Post by Snakeoil » Thu Nov 14, 2019 11:38 am

First, I would use aluminum or copper spacer washers to assure a proper seal.

To Claus' point, did the Russians make their own plugs and did their lengths differ from standard length plugs made commercially by outfits like NGK, Champion, etc.?

I ran into this on my Indian Four. The copy of the original Indian Plug is about 1 thread too long for proper fit in the head. I machined aluminum spacers. These plugs are only required for judging purposes, but the bike must run to be judged. The NGK plugs that I normally run do not need the spacer. Makes me wonder who is making the Indian replica plugs.
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Rob
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propwash
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Re: Getting a spark to fit heads

Post by propwash » Thu Nov 14, 2019 11:57 am

The protrusion into the chamber is OK. If you are worried about piston-to-plug interference, don't be, as it will not happen with a 3/4 reach plug in a head designed for that reach. That head is hemispherical and the piston is flat at the very top. There is room.

Use a washer of some sort. The head is aluminum and it will help seal, distribute the force and keep the head from damage.

The Russian plugs are 12mm or 19mm reach.

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Claus
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Re: Getting a spark to fit heads

Post by Claus » Thu Nov 14, 2019 1:09 pm

Rob, they simply manufactured two types of cylinder heads. One with 18mm and one with 14mm long threads (or as propwash wrote: 12 and 19mm).
So Curt´s old rig has got one new cylinder head somewhen back in the day. I would just leave as is and use matching plugs.
owned bikes: 93 Ural rig domestic model, 95 Suzuki DR 659 RSE, BMW R100GS, Suzuki GSX1100G rig, BMW R100R rig with Ural sidecar, Ural rig with BMW drivetrain under construction,

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Curshe
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Re: Getting a spark to fit heads

Post by Curshe » Thu Nov 14, 2019 9:52 pm

Hmm, 14 and 18 mm heads only? Well have always managed to get a one off if there was one. Both my heads measure 16mm thread depth from the flat seat to the first thread in combustion chamber.
14mm plug short 19mm long can do the spacer and get it about where I want it, couldn’t locate copper, my son has just recently got himself an old south bend lathe with hardly any time on it, so get it set up can make copper or aluminum, :boogie:
Someone has reworked one head because one has stainless seats ,intake guide changed because it was just a bit to long the valve head actually hit it when closed pounding it out.
The guide was still snug when tapped back in place but valve didn’t seat, seat valve and it loosened guide, so I shortened guide cleaned it up put in weld on it see how long it holds.
The other head still has bronze looking seats.
Pulled heads because both sides had oil leaks po said he had done rings so with oil leaks and all the rest wanted to make sure things were in order, bottom end seems tight should get leaks stopped, and hopefully heads a bit better
Curt
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2000 Mt11 Definitely a project runs but broken valve spring loose ring gear rough final drive bearings and worn shocks but is mobile to some extent.
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