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Haven't ever really studied this before but if the heads start with .75 total threads and they are milled .220 that leaves .53 of threads. The guide plates are typically 5/16ths so the stud sits .31 above the milled boss. That brings the total depth to .84(.53 + .31). The difference between the reach of the threads on the stud and the threads in the guide boss is now .84 - .75 which is .09 and that is not much. This puts the bottom of the stud just about flush with the end of the threads in the head. If your original thread depth is different I would still make it a goal to have the stud engagement as close to the bottom of the boss as possible.



I used some sort of supposed thread sealer and I had a stud rattle loose so I switched to red loctite. I haven't had a repeat and the loctite seals the threads as well. If I need to take the stud off a head(which has not been very often) I just hit it with my small torch for just a few seconds and it comes right out.
 

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Discussion Starter #43
I’ve had to many mimosas to follow the math. What’s the thread engagement if you mill the heads .25”
After taking into consideration the guide plates I have about 82% thread engagement on the rocker studs. If I did not have guide plates I would have about 99% tread engagement. The guide plates are taking up thread engagement. This would be best case.
 

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Discussion Starter #44
Haven't ever really studied this before but if the heads start with .75 total threads and they are milled .220 that leaves .53 of threads. The guide plates are typically 5/16ths so the stud sits .31 above the milled boss. That brings the total depth to .84(.53 + .31). The difference between the reach of the threads on the stud and the threads in the guide boss is now .84 - .75 which is .09 and that is not much. This puts the bottom of the stud just about flush with the end of the threads in the head. If your original thread depth is different I would still make it a goal to have the stud engagement as close to the bottom of the boss as possible.



I used some sort of supposed thread sealer and I had a stud rattle loose so I switched to red loctite. I haven't had a repeat and the loctite seals the threads as well. If I need to take the stud off a head(which has not been very often) I just hit it with my small torch for just a few seconds and it comes right out.
Got it. Milling the bosses .220 would have the rocker studs flush at the bottom of the threads. This looks like is the best case scenario when using guide plates. If I go to .250 then I loose .030 thread engagement with the guide plates. That works out to about a loss of 4.5% tread engagement.

The holes in the bosses go through the head into the water jacket. I'd like to give the read loctite a shot but will the red loctite seal the threads good enough to seal out the cooling water? I was going to use PTFE thread sealer from ARP but I like the idea of using the loctite considering my situation.
 

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I put it on somewhat more generously than you would normally apply it and all the way around the threads. I have been running this way for several years now. It has always sealed up fine. You have to make sure and wait your cure out time which I think is 24 hours before trying to run the engine.
 

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Discussion Starter #48
Update: I went to a local machine shop to have the rocker bosses milled down .25" and didn't make out so well. It was Scott's Engine Specialties in Delran, NJ. I spoke to the owner and he wanted $200 for the job. I tried to negotiate but the owner would have none of it. It's obvious he didn't really care if he did the job or not, so I thanked him for his time and left.

I went back to the machine shop that originally rebuilt the heads, Fonse Performance and explained the situation. They immediately realized their mistake and apologized for the inconvenience. They said they milled down the bosses the thickness of the guide plates but did not take into account the thickness of the hex nut on the screw in studs. Bottom line, they milled down the bosses another .25" at no charge.

I measured the length of the threads in the heads after having the bosses milled. All said, I have .510" thread engagement on the rocker studs with the guide plates. 1D thread engagement would be .440". I'm planning on using a good dose of red Locktite on the rocker studs. Wish me luck!
 

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Update: I went to a local machine shop to have the rocker bosses milled down .25" and didn't make out so well. It was Scott's Engine Specialties in Delran, NJ. I spoke to the owner and he wanted $200 for the job. I tried to negotiate but the owner would have none of it. It's obvious he didn't really care if he did the job or not, so I thanked him for his time and left.

I went back to the machine shop that originally rebuilt the heads, Fonse Performance and explained the situation. They immediately realized their mistake and apologized for the inconvenience. They said they milled down the bosses the thickness of the guide plates but did not take into account the thickness of the hex nut on the screw in studs. Bottom line, they milled down the bosses another .25" at no charge.

I measured the length of the threads in the heads after having the bosses milled. All said, I have .510" thread engagement on the rocker studs with the guide plates. 1D thread engagement would be .440". I'm planning on using a good dose of red Locktite on the rocker studs. Wish me luck!

Good Luck!
 
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