Spark Plug help
 

I’m trying to find plugs for my new to me 650 Chiefs.
they have NGK VR5. I’ve looked and can’t find them.

Is there another number stamped in the metal? Not just the one written on the porcelain.
https://cimg9.ibsrv.net/gimg/www.off...3a0fabb5dc.jpg

I don’t believe so. I’ll have to check again tomorrow.

Are you sure it is not the NGK V-Power UR5 2771 plug? That is a common aftermarket head plug.

https://www.ngk.com/ngk-2771-ur5-v-power-spark-plug

That definitely looks like it. Super short

UR5's are a fairly cool temp plug. I ran them in my 525SC.
Basically the same as an AC R41TS

NGK numbers lower is hotter. It is equivalent to AC R43TS.
https://www.sparkplug-crossreference...ert/NGK_PN/UR5

It was a while ago, but now I remember that I went up one heat range from the stock plugs AC41's because they were fouling too easy at idle. For some reason NGK doesn't use the 5 in the UR5 as the heat range. The NGK 6 heat range is equivalent to an AC43, so by the numbers, the UR5 would be about an AC44
NGK sight also shows they are equivalent to an AC R42TS https://www.ngk.com/search/crossrefe...&br=AC%20Delco

Yup, most Merc and performance engine's would use a 6 heat range NGK or maybe if quite cold plug needed a 7 NGK heat range plug.

Here’s the plug.

https://cimg8.ibsrv.net/gimg/www.off...83dbdd338.jpeg
https://cimg1.ibsrv.net/gimg/www.off...626ddfbf3.jpeg