Briggs exhaust port thread ID

[nate0918]

I'm hoping I can get some help identifying the size of these threads on this engine. I picked up a replacement engine for my garden tractor and all is good except for the threads in the exhaust ports. This is a Briggs opposed twin flathead, model 422447. The previous owner tried to thread 3/4" NPT pipe fittings in and mangled the threads. I'm hoping I can clean these up with a tap but I need to identify what they are first. If all else fails, I can use the tapped holes on either side of the port to mount a flange but I'd rather not deal with gaskets. One side isn't too bad but the other is looking pretty taxed. Are these normally 3/4" NPT and the previous owner just overtightened or could these be 3/4" NPS? Any advice is much appreciated.

 

[DJ54]

Looking up the model number engine, then finding an online parts manual showing exhaust parts, it appears that an adapter was used picture below. L&R have different P/N's and different prices.

 

[nate0918]

Right, that is a last resort option that is not original to the tractor. I'll have to take a pic of the exhaust setup and post it later today. The exhaust setup appears to be original and is threaded directly into the ports on the original engine then straight into muffler mounted high and to the front. These engines were used in a lot of different applications so I'm sure there are different setups. If I can keep something close to the original setup I can keep the original heat shielding in place as well.

 

[nate0918]

Here is the original exhaust setup. A thread-in nipple with a slip on exhaust. I'm going to remove it and check the threads.

 

[mrmikey]

I believe it 3/4" NPT

 

[nate0918]

I've read many threads on this trying to figure out what exactly these threads are. I can confirm mrmikey, the threads of at least the stock nipple on the briggs opposed twin engine I have are in fact 3/4" NPT. I removed the original threaded fittings today and they are definitely tapered 3/4"-14 NPT threads. I can also say that the depth of the threaded hole in the block is well past the max engagement. Once the fitting/pipe is as tight as it should get, there is still a good 1/2" of threaded hole left. If you try and tighten any further you will start stripping out the block. Notice in the attached pics that you can get only about 4-5 turns. On a standard pipe fitting that still leaves a lot of exposed thread left. The previous owner of this block kept going and damaged the threads. I'm not a pro at NPT fittings and not familiar with what would be considered normal. Also in my ignorance, I can't confirm what the threads in the block actually are, only what the original fitting was.

 

[RandyT]

I've read many threads on this trying to figure out what exactly these threads are. I can confirm mrmikey, the threads of at least the stock nipple on the briggs opposed twin engine I have are in fact 3/4" NPT. I removed the original threaded fittings today and they are definitely tapered 3/4"-14 NPT threads. I can also say that the depth of the threaded hole in the block is well past the max engagement. Once the fitting/pipe is as tight as it should get, there is still a good 1/2" of threaded hole left. If you try and tighten any further you will start stripping out the block. Notice in the attached pics that you can get only about 4-5 turns. On a standard pipe fitting that still leaves a lot of exposed thread left. The previous owner of this block kept going and damaged the threads. I'm not a pro at NPT fittings and not familiar with what would be considered normal. Also in my ignorance, I can't confirm what the threads in the block actually are, only what the original fitting was.

You do realize that the ring around the fitting with the spikes sticking out is a separate piece and is actually a lock ring that you tighten to hold the fitting in place after installing the threaded portion by hand.