I'm trying to put an engine on the engine stand, but 2 of the bolts will only go in about 3 threads. I ran a tap through and it was a little tight, but it went all the way through. The other bolts go in fine, but the tap is slightly loose on those. I have a junk block from the same year, make, model and the bolts go in without issue. I just got the block back from the machine shop but never had it on the stand. Bolts are, I think, 5/16-24 manual trans bellhousing bolts. What should I do? Get a better tap? Drill and retap? Helicoil?
Are you sure about the bolt size and threads? Could you possibly have gotten your bolts mixed up with some 8mm? Is it possible the machine shop might have run a wrong size or pitch thread chaser through the holes?
I don't think it's different threads. The bolt and tap fit all the holes on the junk block. The tap threads in to all of the holes on the fresh block. The bolts fit all of the holes but 2 on the fresh block. The tap is tight in those 2 holes, but threads all the way in. It's like the holes are compressed a little. The machine shop didn't run taps through anything. They washed the block but didn't even acid dip it, so it's still a bit rusty (I'm disappointed)
5/16 seems to small for bell housing bolts. Could they be 3/8. An M10 wont go in a 3/8 tapped hole but a 3/8 will go in a 10mm threaded hole. Some motors went metric.
Threads can vary but it's unusual to find much variation on the same piece. If you can get all 4 bolts completely threaded with the block off the stand but only 3 threads on a couple of them when attaching to the stand, that seems like the holes in the stand are splayed out of alignment slightly. I'm assuming the holes in the stand aren't threaded. If that's the case, you may need to open or enlarge the holes slightly with a rattail file or similar. You have tried chasing a tap into the block but how about running the 2 tighter bolts into a die? The dies that I have appear to have a 'set screw' to adjust them slightly for girth. I don't recall if I have ever tried that myself but it may be a fix for your problem. If you are near a hardware store you could try getting a pair of bolts on the chance that they will work out better. Good luck..... you've got more brains than those bolts so don't let 'em beat you.
Did you use a “ bottoming” tap? Is there dirt in the bolt holes? I assure you if you tapped the bolt holes properly, the bolt, if in good condition and correct size, will go in the hole! Bones
But the bolt threads on a grinder so it`s tapered a bit. Finish it off on the wirewheel. It should make it easier to line the bolts line up.
I’m guessing that sometime in the past, this block has been worked on by someone that changed these bolt holes . Just because a tap threads into the hole doesn’t mean the threads are good . I’m thinking someone rethreaded the holes to a different size bolt pitch . Or,,,,used fine thread bolt’s because that was all they had,,,,,,stranger things have happened . And,,,,as has already been asked,,,,,we don’t know what kind of engine is being worked on . Tommy
What kind of engine ? Bitching about the machine shop from a guy that can't figure out a bolt holes size is a bit premature . What block takes a 5/16 bolt for a bellowing?
Simply taking the bolts that do thread in freely and trying them in the holes that don't screw freely tells you if there is a problem. Threads do get grit and rust in them as well as getting deformed. Running the correct size tap tru them should clean it out. BUT.......it is possible that someone didn't have the right bolts on hand or mistakenly ran a metric tap thru the hole. I would try a metric bolt and see if it does work, just to see if someone screwed (pun intended) it up. At that point you have to decide whether to stay metric or attempt to return to American Standard threads. Either choice may not have sufficient metal left to hold a bolt. You can only try it to see what happens. If its weak or stripped at that point move up to a 7/16-14(coarse thread) (Fine thread is 7/16-20. Use coarse. Drill to appropriate size before tapping with the larger tap. Probably need to enlarge bellhousing holes. Also, don't forget to check bellhousing alignment. Its much easier to do while the block is on a table rather than installed in the car. Simply put the cran in using old main bearings and bolt the housing in place. Then indicate it and see if you need to change to offset dowel pins. And last, make sure the bore in the housing is the correct size for your transmissions front bearing retainer. Chevy had two different sizes and you "have to have" the correct size.
Chill out dude, @Hellfish has been here for a couple decades. We all run into something that escapes us from time to time. And WTF is a "bellowing"?
Nowhere in my thread did I bitch about the machine shop. I simply said it just came back from the machine shop "but I never had it on the stand" which implies that I never tested the threads. I don't even know how a machine shop could screw up the bellhousing threads. And I know how to tell bolt size and pitch. 3/8-24, but I wasn't home when I posted that. Sheesh. What's a "bellowing"? So, it turns out that the threads were rusty (which I knew), but the cheap Chinese tap I was using was just a little undersized , so it would thread in, but not clear enough of the threads for the good bolt. I tried a different, quality tap, and then the bolt went right in. My clue was that " the tap is slightly loose on those" Thanks all for offering solutions and suggestions!
Maybe the hole does not identify as a bellhousing mounting bolt hole . maybe it wants to be a water outlet , or an oil gallery , or maybe a wheel stud Glad ya figured it out and quit your Bellowing
I can't imagine if you have, let's say, a 7/16" tap and thread a hole with it, then try to put in a 7/16" bolt that the bolt wouldn't fit. The bolt should fit any matching hole that's been threaded with a matching tap size. So it sounds like either wrong size tap, metric vs american, or a cheap undersized Chinese tap that doesn't meet standards. ....
He might get better help if he said what kind of engine it is so it can be determined what is correct to start with . There are metric and standard bolts that share a near identical thread pitch so a tap might screw in as the TPI is correct but the hole size is wrong . I spelled bell housing wrong even though its obvious what I meant . I doubt the hole got smaller by someone going to a different size . So unless it has had a incorrect bolt or tap forced into it, the hole size of this tight hole is original size the question is if the thread pitch original? As he figured it out its mute point now . Wasn't a attack .
Well your disappointed then as that is what you said . Glad you got the block holes figured out on whatever it isyour working on . I did get a Nissan forklift block/ engine back once and a shop had tried to force a incorrect bolt in when they had tried to put it on a stand or had tried to use a lifting eye on the back. Again wasn't a attack or at least wasn't meant to be . Hope the assembly goes better .
just a suggestion, get a fresh tap of the correct size. there is probably minor obstruction in the threads that a worn out tap is not cleaning out.
I went threw a similar situation the other night , On a full competition aluminum oil pan where the Studs & bolts are on the inside of pan , when reinstalling pan I had problems , nut would go a few threads then jam like wrong thread pitch , I pulled pan to remove studs, I was sure nut side was 1/4 fine, looked @ threads , Good tried installing nut in hand , same thing ,afew threads then jam, grabbed my thread pitch gauge , 1/4 fine. Grabbed my dies ran up the threads smooth, ran tap threw nut ,smooth , nut to stud same thing , a few threads then jam. Use brake clean ,Still would jam. Then used thread chasers , tight on both nuts & studs, but was able to screw full threads but with about 1 pound of resistance/pressure, So then I used brake clean brass pipe brushes , I found that there was about ((guessing here on thickness)) .000?? something of lock tight that tap & die (sap & mac) would skip over but thread chaser would not. A 20 mint oil pan drop & re install took me over 2 hrs
As I recall it was a J15 in fact . Seems like the head bolts were real close to a standard thread . Its been a while. Good little engines for what they were in .
From experience I can tell everyone that taps do wear with use and abuse and just trying to tap different types of metal. I have been lucky enough to get lots of taps and dies along lifes way. LOTS. I find that very often these quality taps dull over time and don't cut as well or don't cut fully. They appear to be in good shape with no obvious issues.........but they get into the hole and become difficult to continue. Try another tap.....sometimes its hard to cut as well. This is especially true with the very small easily broken taps. Anyone who has broken a tap in a blind hole can tell you its not a fun experience. Personally I have found that drilling the hole slightly larger than the size stated on the thread/drill chart helps a lot. Also, switching to a different tap will OFTEN resolve the problem that a dull tap is fighting. Sometimes you also have to deal with softer and more "gummy" steels like 1010/1020 that clog the tap. There are lots of little nuances to threading things. Most times there isn't a problem and everything works well, but from my experience, slightly enlarging a threaded hole size and using a new tap along with some oil usually solves the problem. Like all examples, there are exceptions to what I just said, but generally this works just fine.
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