Engine Trouble Quick question CNC “Racing Heads”.

Carl Walichnowski

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I recently had. CNC Racing Head put on my MB and I’m currently trying to trouble shoot cause my motor will not turn over. I’m wondering if I’m getting enough spark cause the head is so big. If this Is the issue is there any larger spark plugs to use because this one seems too small. Or how else can I fix the problem??
 
View attachment 82187 View attachment 82188 View attachment 82189 I recently had. CNC Racing Head put on my MB and I’m currently trying to trouble shoot cause my motor will not turn over. I’m wondering if I’m getting enough spark cause the head is so big. If this Is the issue is there any larger spark plugs to use because this one seems too small. Or how else can I fix the problem??
If your using the head pictured it may well require a longer reach plug, NGK has a NGK 7333 BP6ES Standard Plug that I think should work for you or NGK 1034 BP7ES Standard Plug.
 
That's what I originally thought I needed to use with the MZ "R" head, but the piston hit the ground strap and closed the gap. The NGK BPR7EIX was just that little bit too long.
The E refers to the length of the threaded section.
I think they should have made the head thick enough for the E length plug because a bit extra thickness there would make it easier to unscrew my compression tester.
Anyway as it is, with the BPR6HIX there's some threads inside the head that aren't covered by the plug, so they're bound to hold onto sooty deposits which I hear can glow and be a cause of pre-ignition or whatever it's called.
It's like they made the head just in between the spark plug sizes so that it is impossible to get a plug that's exactly right. :rolleyes:

So choose carefully. Before buying a new plug with the E length, check the clearance under the ground strap with your H length plug. Use some soft putty like Play Dough maybe or make some dough? Idk. :oops:

As you can probably tell I forgot what the measurements are that the H and the E refer to. I think H is 10mm and E is 14mm long, but I'm not completely sure so you best Google a chart of NGK plug codes.

Anyway I don't think a too short plug would prevent starting. A too long plug would, if the gap is squashed closed by the piston.
If you have difficulty turning over the engine then maybe that's just the high cranking pressure?
If the engine will not turn over even when the plug is out, then maybe you don't have a thick enough head (or base?) gasket and the piston isn't clearing the head at all. o_O
 
View attachment 82187 View attachment 82188 View attachment 82189 I recently had. CNC Racing Head put on my MB and I’m currently trying to trouble shoot cause my motor will not turn over. I’m wondering if I’m getting enough spark cause the head is so big. If this Is the issue is there any larger spark plugs to use because this one seems too small. Or how else can I fix the problem??
Can you show us a pic. of the inside of the head with the plug installed? I have a after market head that is to thick at the threads to allow a regular plug to reach properly into the chamber. While it did start it ran like s**t so I'm figuring it's cause the spark is to hidden.
 
The plugs Ryderz is showing have a 3/4" reach. I am going to try one and use plug index washers if it is to long. H=1/2" E=3/4"
 
Well I had this similar non starting issue happen to me when I first switched the head over about a year ago and I took that lil metal nipple thing off of the spark plug but while that did help my MB still ran like crap so I went back to the original stock head. Now alot has happened over the last year, a few minor upgrades and I had the whole kit switched over to a new frame and we once again put this square head on. Now the motor would kick over with the head and spark plug as it is but the engine would die within 1/4 mile and even then it ran like crap. After decribing the issue in a different thread the majority pointed to carb issues but after putting in a new carb I still can not turn the motor over rergardless of what I do, I'm wondering if I'm back to my old problem which seems reasonable.
 
Can you show us a pic. of the inside of the head with the plug installed? I have a after market head that is to thick at the threads to allow a regular plug to reach properly into the chamber. While it did start it ran like sh*t so I'm figuring it's cause the spark is to hidden.
I'll be trying to fix the problem this weekend so I can take pics of the plug in the head then. Is it possible to suggest a plug just based off of the pic?
 
The B5hs should work for most heads its what I'm using for the cnc head I have although that's a different type you have. I have the smaller saucer type. Theres maybe 1 or 2 threads that the plug doesn't thread in at the bottom. I think it will be fine. Did you gap the plug?
 
I'll be trying to fix the problem this weekend so I can take pics of the plug in the head then. Is it possible to suggest a plug just based off of the pic?
It's hard for me to button it down for you without seeing the plug in the head. The plugs that Ryderz has shown both have extended electrodes so they will extend even a little farther into the chamber than a (2877 B7ES) which is what I am going to try. All three have 3/4" reach where as a B7HS Shown below is 1/2". They make plug indexing washers in varying thicknesses so you should be able to get it just right. The plug Will is talking about is to hot and only has a 1/2" reach so no it's not your answer.
 
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Oh ya one more thing about the 2877 B7ES is the top doesn't screw off so your plug boot will need to be a automotive type. As Furry was saying NGK doesn't seem to offer one between 1/2" and 3/4" reach. I am going to look into some other brands to see if they offer a plug in a similar heat range to 7 with a 5/8 or 11/16 reach.
 
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