[papereater]

People,

Planning ahead of next week's car project, my 1987 Sunbird GT, time to replace the seal (donut) between exhaust manifold and exhaust pipe. I have the bolt/seal/spring set. Car has 214,000 miles on it, and of course, it is 32 years old and Im concerned that those old bolts may not just unscrew out, that they may be fused. has anyone ever done this?

Now, the instruction sheet from Felpro says to chase out those 2 threads. I am searching for the right tap, and measured the diameter of the bolts and looks like they are 10MM. But when I take my 10mm tap and try to "test" it by threading it into the nuts that came with the bolts it is too tight. Dont want to force it. Maybe they are NOT metric?

Anyway, comments on both fused old bolts and tap size appreciated. I hope this wont be a 1-2 week project chasing (pun??) around to prepare those bolt holes.......

Thanks.

 

[Windows on Wash]

Start soaking them now...everyday.

Acetone and Transmission fluid mix.

 

[huesmann]

Could be coarse thread (1.5mm) where your tap is fine thread (1.25mm). Or vice versa.

If you already have the bolts, take them to HD and use their bolt identification tool to confirm dia and pitch.

 

[papereater]

I will go to HD, but from what I hear pitch is measured by counting the threads over a distance, then divide distance in mm by thread count, example, 23mm length divided by 16 threads = 1.44. That is neither 1.25 nor 1.5, (scratching scalp, confused)........Oh well.

 

[ukrkoz]

10mm 1.50 1.25

 

[papereater]

10mm 1.50 1.25

But UK, why do I get 1.44? Something is not right. Either my metal metric ruler, or something else.

 

[SeniorSitizen]

3/8" - 16 was common for those studs unless you know for certain they are metric.

Thread pitch = the distance from one thread to the corresponding point of the next thread.

 

[papereater]

3/8" - 16 was common for those studs unless you know for certain they are metric.

Thread pitch = the distance from one thread to the corresponding point of the next thread.

Wow- surprise! Yup, I suspected maybe they are not metric. We dont know for sure yet, but tomorrow I am planning to stop by HD and try what Huesman said. No other way to know. unless, I call felpro tech service tomorrow- yeah- good idea, they gotta know.

Thanks. I will advise asap.

 

[SeniorSitizen]

Do you have a set of feeler gauges? Those in conjunction with a adjustable end wrench ( Crescent ) can be a fairly accurate caliper.

 

[Oso954]

but from what I hear pitch is measured by counting the threads over a distance, then divide distance in mm by thread count, example, 23mm length divided by 16 threads = 1.44.

You either heard wrong or are remembering it wrong. Thread pitch (metric) is a simple measurement from the peak of one thread to the adjacent thread peak. If you are looking at a 10mm bolt, the fine thread (1.25mm) vs coarse (1.5mm) you need to be precise enough to pick up the 0.25mm difference.

US threads are typically threads per inch (tpi).

This will explain it better.
https://www.boltdepot.com/fastener-information/measuring/tpiandpitch.aspx

If you hit the links on that page, you can see the typical tpi or pitch for Some metric and US bolt sizes.

 

[papereater]

You either heard wrong or are remembering it wrong. Thread pitch (metric) is a simple measurement from the peak of one thread to the adjacent thread peak. If you are looking at a 10mm bolt, the fine thread (1.25mm) vs coarse (1.5mm) you need to be precise enough to pick up the 0.25mm difference.

US threads are typically threads per inch (tpi).

This will explain it better.
https://www.boltdepot.com/fastener-information/measuring/tpiandpitch.aspx

If you hit the links on that page, you can see the typical tpi or pitch for Some metric and US bolt sizes.

Thanks Oso. I just figured I would minimize my error if I counted over a longer span as I dont have such a high precision tool. Anyway, looks like Im on the right track. Looking more and more that is is not a metric like Senior said.

 

[sestivers]

I wouldn't have guessed a Pontiac to use metric fasteners. Was it rebranded by a Japanese mfr? Are the other engine fasteners metric?

 

[ChuckF.]

Quite possibly not metric; on older design engines that have been around for decades they don't change fasteners to metric for no good reason. My Dodge truck has some of each.

If you don't have a thread gauge, try putting in known bolts from your stock.

 

[huesmann]

You either heard wrong or are remembering it wrong. Thread pitch (metric) is a simple measurement from the peak of one thread to the adjacent thread peak. If you are looking at a 10mm bolt, the fine thread (1.25mm) vs coarse (1.5mm) you need to be precise enough to pick up the 0.25mm difference.

But it sounds like that's exactly what the OP is doing—measuring X distance over Y number of threads, and dividing X by Y, which gives thread pitch in mm (assuming measured in mm!). If you can only measure one thread then the 0.25mm precision matters, but measuring over many threads will give you a decent result even if your measurement tool is only 1mm accurate.

 

[Bigplanz]

Thread pitch gauge. They have them for SAE and Metric. Easiest thing to do is take it to HD or Lowes and find out what the nut threads on to.

https://www.lowes.com/pd/IRWIN-Stan...6Zck2Q4BBZZl8SMtuvYry_1Ir8jI4LVhoC4G4QAvD_BwE

 

[SeniorSitizen]

Unless I'm mis-reading the OP, his Pontiac exhaust manifold has studs. Although fine threads are superior on many applications I've never seen fine threads on manifold studs, possibly on the nut end but not on the manifold end.

 

[SeniorSitizen]

QUOTE:
I have the bolt/seal/spring set.
********************************************************
Please tell us exactly what bolts are in this set. If you can't post a picture just describe those bolts.

 

[Oso954]

But it sounds like that's exactly what the OP is doing—measuring X distance over Y number of threads ......

Look at the link I provided. TPI is measured from valley to valley over one inch.

Thread pitch is measured from peak to peak. It you are going to measure it over a distance, you need to be starting and ending the measurements in the right place.

Starting and ending in the valleys would throw the total length off.

 

[papereater]

I wouldn't have guessed a Pontiac to use metric fasteners. Was it rebranded by a Japanese mfr? Are the other engine fasteners metric?

Sorry for late reply, Ses. 99% of the car's bolts are metric, like all other cars(?).

I have nnot yet had a chance to try to size it at HD. New Year Hype ans all going on.........

 

[papereater]

Unless I'm mis-reading the OP, his Pontiac exhaust manifold has studs. Although fine threads are superior on many applications I've never seen fine threads on manifold studs, possibly on the nut end but not on the manifold end.



https://youtu.be/cTRUXRv2HFs

Great video, Senior! I looked all over and coundnt find anything having to do with exhaust manifold bolts. Good to know. But man, what a chore- I might have to remove the whole thing and put a torch on it. All I have is propane.