Thread Chaser or Tap?

[R_W_B]

Ok, I have a full set of taps and dies that I would like to use to clean up the rust and old loctite from all the threads of items I have pulled off my old truck. However I have been told in the past (from various sources) that using a tap to clean threads will cut new material and cause the thread to be loose when reassembled. Various sources told me that a thread chaser was in order for such. You know the kind you see all the time at the auto parts store for spark plug holes, only to buy a whole set they come also in kits.

A set of needed thread chasers (in a kit) will cost me $60. So not wanting to part with $60 right now I did a lot of thinking about this. I could not figure how a tap would cut new material from a hole that was cut with the same size tap.

So I posted this same question on a truck forum and got pretty much a 50/50 mix of opinions. Some for chasers, other said just use the taps. So wanting to get the real truth on it I posted the question on a Machinist forum (yea I belong to a lot of forums).

Amazingly many folks on the machinist forums had not ever heard of a thread chaser. I'm posting the one most convincing reply from the machinist forum below. I welcome comments from you guys on this. But at this point I'm thinking I don't need to buy the thread chaser kit.

====paste from machinist forum===
If the threads are really cruddy and rusty then you will damage the tap, not the thread. The tap acts as it's own lead screw and once it is in one full revolution it is not going to cut anything that is where it should be. If the thread is deformed and material is in front of the cutting edge it will be removed and should be.

If they finding threads looser after cleaning the rust and such out the remember that the rust is part iron and yes it will be looser, but not because of the tap, but because metal has been removed by rusting.

I am in the power generation industry. When we disassemble a turbine we clean every thread. We stard with a wire brush and if that doesn't do it we run a tap or die. It's the last resort because rust and grit will ruin a 500 dollar tap in one hole.
======end of machinist forum paste===

 

[Hoople]

I could not figure how a tap would cut new material from a hole that was cut with the same size tap.

Either did I until I tried it. Especially if the item is aluminum or soft metal. Using a tap to clean threads is the kiss of death.

Don't ever try it on your spark plug holes. You will regret it.

 

[Redfish-Joe]

Give this a quick read.

Chasing Threads - Car Craft Magazine

 

[R_W_B]

One thing if for sure I seem to have a knack for spotting items that fall into "gray" OR "difference of opinion" areas. I had already bought a spark plug chaser to do all my plugs holes.

But as I got further into the engine I kept finding things that made me go deeper. I currently have the all the front bracketed items off (which is quite a few items on my truck), the water pump, the exhaust and intake manifolds and the heads. The cylinders (thankfully) look ok, so I can finally stop pulling things off.

The heads are gone to a local machine shop for a valve job. Anyhow I've got all kinds of thread conditions that I'm cleaning up. Some with grease gunk, some with old loctite, and others (like the exterior bracket items and the exhaust with some serious rust build up. The wire brush things do work good on everything except hard loctite and hard rust. For them you need a chaser or die.

Thanks to the input I've gotten across all the forums I asked this on I feel that I have what I need to make an intelligent decision. It was amazing the split of opinions I got on the auto truck forums (about 50/50) and the 90/10 replies at the machinist forums. The machinist forums were like "what's a thread chaser". But then when I think about it they are in the business of new threads and not so much cleaning up old ones.

The one 10 (of the 90/10) on the machinist forum said this.
[-- The only time the finished threads will be slightly less than the tap size is when the scenario (varies by material and size of tap) where the material "springs back" after the tapping if finished. Sometimes the tolerance is acceptable and it is left in it's "sprung back" state. Other times an additional tap is warranted to bring within tolerance --].

One thing that was agreed across "all" forums asked, were these points when cleaning threads.
1. Always start the tap (or chaser) by hand and make sure it is going in straight. At the first sign of resistance, back it off and (still by hand) start it back in. It's a 2 steps forward and 1 step backward process.

2. Give it plenty of oil during the process.

3. If you have an extremely rusting or gummed up set, then use a T-wrench but apply only "just" enough pressure to go the 2 steps, then back off. If it moves "too" hard your threads are probably rusted beyond repair.

Will I buy the $60 set of chaser's, well that's still a good question for a guy like me. I will try each item by feel, and given everything that I've collected I can decide then. BTW for a little more than a buck a piece I'm buying new head bolts. But I still need to clean the block threads for them. And a bunch of other bracketed items and exhaust and intake manifolds.

I've got the pushrods and rockers all sorted out in the same order they came off but I still have to clean the pushrods up some to get them clean enough to roll across our dining room table to make sure they don't wobble. The rockers ain't cracked or galled or excessive wear so I feel pretty good bout them for 158,xxx miles.

Anyhow I've got plenty to do on it in between doing some building repair right now.

Oh and also, there was some agreement that some of the cheaper China made carbon steel tap and die sets make pretty good thread chasers but will only last 1 or two original metal taps before loosing their cutting edge.

 

[Old Mike]

One thing if for sure I seem to have a knack for spotting items that fall into "gray" OR "difference of opinion" areas. I had already bought a spark plug chaser to do all my plugs holes.

But as I got further into the engine I kept finding things that made me go deeper. I currently have the all the front bracketed items off (which is quite a few items on my truck), the water pump, the exhaust and intake manifolds and the heads. The cylinders (thankfully) look ok, so I can finally stop pulling things off.

The heads are gone to a local machine shop for a valve job. Anyhow I've got all kinds of thread conditions that I'm cleaning up. Some with grease gunk, some with old loctite, and others (like the exterior bracket items and the exhaust with some serious rust build up. The wire brush things do work good on everything except hard loctite and hard rust. For them you need a chaser or die.

Thanks to the input I've gotten across all the forums I asked this on I feel that I have what I need to make an intelligent decision. It was amazing the split of opinions I got on the auto truck forums (about 50/50) and the 90/10 replies at the machinist forums. The machinist forums were like "what's a thread chaser". But then when I think about it they are in the business of new threads and not so much cleaning up old ones.

The one 10 (of the 90/10) on the machinist forum said this.
[-- The only time the finished threads will be slightly less than the tap size is when the scenario (varies by material and size of tap) where the material "springs back" after the tapping if finished. Sometimes the tolerance is acceptable and it is left in it's "sprung back" state. Other times an additional tap is warranted to bring within tolerance --].

One thing that was agreed across "all" forums asked, were these points when cleaning threads.
1. Always start the tap (or chaser) by hand and make sure it is going in straight. At the first sign of resistance, back it off and (still by hand) start it back in. It's a 2 steps forward and 1 step backward process.

2. Give it plenty of oil during the process.

3. If you have an extremely rusting or gummed up set, then use a T-wrench but apply only "just" enough pressure to go the 2 steps, then back off. If it moves "too" hard your threads are probably rusted beyond repair.

Will I buy the $60 set of chaser's, well that's still a good question for a guy like me. I will try each item by feel, and given everything that I've collected I can decide then. BTW for a little more than a buck a piece I'm buying new head bolts. But I still need to clean the block threads for them. And a bunch of other bracketed items and exhaust and intake manifolds.

I've got the pushrods and rockers all sorted out in the same order they came off but I still have to clean the pushrods up some to get them clean enough to roll across our dining room table to make sure they don't wobble. The rockers ain't cracked or galled or excessive wear so I feel pretty good bout them for 158,xxx miles.

Anyhow I've got plenty to do on it in between doing some building repair right now.

Oh and also, there was some agreement that some of the cheaper China made carbon steel tap and die sets make pretty good thread chasers but will only last 1 or two original metal taps before loosing their cutting edge.

In another life, when I worked for a living, I was a Journeyman Machine Repairman so I have a pretty good knowledge of taps and dies. We almost always chased when assembling equipment, the way to do it correctly is with a good tap or die and Tap Magic cutting fluid and go slow backing up frequently and blowing off the part with compressed air. One more thing, buy American, a good set is going to cost you a lot more than $60 but a cheap set will ruin your work.

 

[Jack Klarich]

Dave, it is always a good idea to replace the head bolts on todays engines, you should always tap the head bolt holes in the block to clean out the threads of any sealant to ensure a proper torque, you may need to use 3 torque step the last being degrees, lightly scuff the block mating surface before installing the gaskets, check the rocker arm fulcrums for cracks

 

[horizonchaser]

In another life, when I worked for a living, I was a Journeyman Machine Repairman so I have a pretty good knowledge of taps and dies. We almost always chased when assembling equipment, the way to do it correctly is with a good tap or die and Tap Magic cutting fluid and go slow backing up frequently and blowing off the part with compressed air. One more thing, buy American, a good set is going to cost you a lot more than $60 but a cheap set will ruin your work.

Mike, you didn't happen to work in Glass Bottle Mfg. business by any chance did you? Just wondering.

 

[Old Mike]

No, automotive industry

 

[R_W_B]

In another life, when I worked for a living, I was a Journeyman Machine Repairman so I have a pretty good knowledge of taps and dies. We almost always chased when assembling equipment, the way to do it correctly is with a good tap or die and Tap Magic cutting fluid and go slow backing up frequently and blowing off the part with compressed air. One more thing, buy American, a good set is going to cost you a lot more than $60 but a cheap set will ruin your work.

Dave, it is always a good idea to replace the head bolts on todays engines, you should always tap the head bolt holes in the block to clean out the threads of any sealant to ensure a proper torque, you may need to use 3 torque step the last being degrees, lightly scuff the block mating surface before installing the gaskets, check the rocker arm fulcrums for cracks

Jack the mechanics guys told me to just reuse the head bolts (they said they do it all the time in commercial auto shops) but when I found out they were only about a buck a piece I had already put some Fel-Pro head bolts on will call order. I don't want to risk a thread failure during the torque process and have to pull the rest and start over. The machine shop is closed for Christmas the rest of the week so I haven't heard yet if they will have to shave the heads any. It's a good shop, they've been around since I was a kid.

Mike I respect your input and professionalism, and thank you for replying to my question since "all" of the replies is what I needed to make an intelligent decision based on my scenario. However I am not going to spend big bucks on an expensive tap and die set which I would probably ruin in short order on a bunch of rusty and gooped up motor parts.

I have a set I inherited from my GrandDad that has not been used that much. It looks to be a cheaper carbon steel grade set. My GrandDad raised 4 girls working as a prison guard and delivering fuel oil so I'm sure he was not in a position to spend big bucks on it. It says on the case "Made in Japan" so that's a step up from Made in China as far as quality goes. Japan has produced hundreds of millions of motorcyles and cars over the past 50 yrs and Honda has been the world's largest motorcycle manufacturer since 1959. So I figure they can make a tap and die set ok.

I used the die's on a good many of the bolts today which good success. Some of the really bad bolts I had to cut into the rust with a knife just to find the threads. These are bolts that bolt bracket items on and also intake manifold bolts that have threads exposed to water jackets. I almost threw them in the trash, but decided to see what I could do with um. Amazingly they came out looking pretty good.

It's tedious dirty work and I use engine degreaser for lube since they are in such bad shape. The fumes can make your eyes water some. But it makes like new bolts out of what was basically junk. I put a thread guage on them afterwards and I can see no real difference in metal mass. The thread gauge still fits tight on them like on a new bolt. I also noticed that "some" very thin loctite residue actually survived the process and is still stuck to the sides of the thread (not in the valleys or peaks) so that seems to prove to me that the die is not cutting thread metal.

I still have to do the hole taps yet so I don't know yet how they will go. I definitely will blow the hole out often with some air. They are not as rusty either and in better shape. I would say for spark plugs I tend to agree with Hoople and go with a chaser (or really dull tap) and here's why.

1.Spark plug holes are fine threads and not very deep.

2.Spark plugs are exposed to extreme operative conditions that tend to "weld" the plugs to the heads (especially aluminum heads). So a chaser would be more forgiving if you didn't have it lined up perfectly.

However EVEN with a chaser, you really need to get everything going in "right" and follow all the correct procedures or it's gonna foobar for sure no matter whether it's a tap or a chaser. I thank you all for your input, it kept me from going in blind.

 

[Jack Klarich]

Jack the mechanics guys told me to just reuse the head bolts (they said they do it all the time in commercial auto shops) but when I found out they were only about a buck a piece I had already put some Fel-Pro head bolts on will call order. I don't want to risk a thread failure during the torque process and have to pull the rest and start over. The machine shop is closed for Christmas the rest of the week so I haven't heard yet if they will have to shave the heads any. It's a good shop, they've been around since I was a kid.

Mike I respect your input and professionalism, and thank you for replying to my question since "all" of the replies is what I needed to make an intelligent decision based on my scenario. However I am not going to spend big bucks on an expensive tap and die set which I would probably ruin in short order on a bunch of rusty and gooped up motor parts.

I have a set I inherited from my GrandDad that has not been used that much. It looks to be a cheaper carbon steel grade set. My GrandDad raised 4 girls working as a prison guard and delivering fuel oil so I'm sure he was not in a position to spend big bucks on it. It says on the case "Made in Japan" so that's a step up from Made in China as far as quality goes. Japan has produced hundreds of millions of motorcyles and cars over the past 50 yrs and Honda has been the world's largest motorcycle manufacturer since 1959. So I figure they can make a tap and die set ok.

I used the die's on a good many of the bolts today which good success. Some of the really bad bolts I had to cut into the rust with a knife just to find the threads. These are bolts that bolt bracket items on and also intake manifold bolts that have threads exposed to water jackets. I almost threw them in the trash, but decided to see what I could do with um. Amazingly they came out looking pretty good.

It's tedious dirty work and I use engine degreaser for lube since they are in such bad shape. The fumes can make your eyes water some. But it makes like new bolts out of what was basically junk. I put a thread guage on them afterwards and I can see no real difference in metal mass. The thread gauge still fits tight on them like on a new bolt. I also noticed that "some" very thin loctite residue actually survived the process and is still stuck to the sides of the thread (not in the valleys or peaks) so that seems to prove to me that the die is not cutting thread metal.

I still have to do the hole taps yet so I don't know yet how they will go. I definitely will blow the hole out often with some air. They are not as rusty either and in better shape. I would say for spark plugs I tend to agree with Hoople and go with a chaser (or really dull tap) and here's why.

1.Spark plug holes are fine threads and not very deep.

2.Spark plugs are exposed to extreme operative conditions that tend to "weld" the plugs to the heads (especially aluminum heads). So a chaser would be more forgiving if you didn't have it lined up perfectly.

However EVEN with a chaser, you really need to get everything going in "right" and follow all the correct procedures or it's gonna foobar for sure no matter whether it's a tap or a chaser. I thank you all for your input, it kept me from going in blind.

Dave, Most Felpro gasket sets IE Head gasket kits come with new head bolts now, these are torque to yield bolts and should not be re used, If this is a chevy 4.3 motor do not take any chances