Since its an Austin Healy Sprite, the first thing you need to do is determine exactly what thread you have. Seems wrong that a British Sports Car would have American Standard threads. If its not an American standard thread, the British had several possible threads that may have been used. If its not American Standard threads, then did you look up the torque value in an American Reference Table or get it from some book dedicated to Austin Healy? I never fooled around with an Austin Healy, but I worked on a few British motorcycles.......so I'd do a little checking to find out what you actually have.
The con rod cap screws are British standard fine threads at 20 tpi a little coarser than 3/8 SAE nf . The only torque data I have is in the Austin Healey Sprite manuals I couldn’t find any charts for British standard fine threads. The manual says 35 ft lb of torque.
Do the bolts you have .....have a raised number on top signifying the "class" of the bolts......8.8 or 10.9 ? If you look at the Metric Fastener Chart on the attachment below, you will see that the different class bolts have different torque values. I'm guessing you have a 10mm bolt which should be about the same diameter as a 3/8 but slightly larger. If you can find some direct replacement bolts, I'd consider replacing them, otherwise I'd just reuse what you have and cross your fingers. You might want to post a picture of your existing bolt and maybe the rod and cap assembly. Torque-Tension Reference Guide.pdf (fastenal.com)
Received theARP rod bolts, installed and torqued to 35 lb ft measured 0.0002 - 0.0003 out round 45 lb ft measured 0.0002 - 0.0003 out of round 55 lb fly measured 0.0002 - 0.0003 out of round No distortion that I can detect 0.0002 is probably my limit for accuracy using snap gauges and mics I also installed rods torqued to spec and spun on crank to see if I had any tight spot No tight spots. Checked clearances 0.0015 Measured bolts at torque Start 1.87 35 lb ft 1.876 45 lb ft 1.880 55 lb ft 1.885 spongy feeling 55 lb ft 1.890 Relaxed 1.886 Looks like the yield is close to 55 lb ft Glad I changed bolts also looks like new cap screws may not distort the big end. Thanks all, Dan
Not trying to be a "smarta**" here......... I just want to clarify something. I know people often have to make do with what they have or can afford. Using a snap guage and a micrometer is a decent attempt at insuring nothing is majorly off, but its not a reliable way to measure .0002 (2/10,000 ths)of an inch. I'm pointing this out simply so other builders don't think this is the acceptable way to measure a rod bearing. There are several ways that will give acceptable and repeatable readings but some of them aren't found in home shops. My suggestion for anyone trying to measure the inside of a rod bearing would be to buy a "dial bore guage" and a standard thats close to the size you want to measure. The "standard" is a round ring thats precision ground. It doesn't have to be the exact size you want to verify, but if its close/in the general area then a builder should be fine. The other option is to purchase an "intrimik" and a standard. The dial bore guage needs to be one that has .0001 increments, not .001 The ring guage would be found "used" on Ebay. New ones are expensive but I have seen some new ones that were not too expensive. Intrimiks will be a "used" item off Ebay as well and you need the ring guage to make sure they are correct or so you can adjust them. What I'm trying to point out is that when checking any part, you will get some reading and think that its correct, but if the tool/guage you are using is not really accurate.........the person is fooling themselves. Many things do not need to be within .0002 to operate OK. So if someone thinks they have an accurate reading and the part works ok....then they assume their method for checking the dimension is fine. It could just be that the particular thing being measured is actually out of tolerance but still works. If the item is out of tolerance on the large side creating more clearance it will usually function OK. If its out of tolerance on the small side however, it may sieze up. Like I said, not trying to be a smarta** here, just trying to help people understand what they really need when measuring close tolerances.
Ekimneirbo I agree wholeheartedly. When I’m using snap gauges I take several measurements at each point. I take measurements at three spots on both sides of the rod journal so six points and three or four measurements at each point to assure that my measurements are consistent. On this engine ,upon tear down the bearings and crank looked beautiful. I checked the old bearing to journal clearance with plasigage and had 0.0015 to 0.0017 clearance well within spec I didn’t have any machine work performed on the crank or rods. I polished the crank with 600 grit and crocus cloth. Had I not over torqued the rod cap screws I wouldn’t have given any more thought to the rod and crank Using my somewhat crude measurements I am reasonably sure everything will work just fine I will not be turning this engine past the factory red line. Someday I will buy I dial bore gauge and standard when my budget allows. For me like many it comes down to $$$s. I agree that getting everything to a high degree of tolerances is best, but that can be a deep rabbit hole - torque plates , running coolant through block while boring/honing ,custom crank ,rods ,pistons , line boring , head flow work by a pro etc etc etc Damn I should’ve been born a kazilionaire
ekimneirbo: Thanks for the excellent info. and advice. It was more than informational. It was educational.
I had no idea there were ring gauges. But makes sense there are. Would definitely save some steps on how I measures ID’s for sure. I zero my bore gauge, write things down, then set my micrometer up in the vice, look at the deflection. To be honest it’s a PIA. Lol. Good info!
Best to have a buddy with a good machine shop and better measuring toys than I have. I have gone over to use his surface plates, took home a dial-bore gauge to check a block. I have used his Sunnen gauges at his shop. I have never had to use his Sunnen hones... yet. But they are always there.
Just for informational purposes, let me explain the RING guage a little more. In a perfect world all parts would be measured at an ambient temperature thats always the same. Metal things/parts expand and contract as the temperature changes, and that includes the measuring tools and standards we use. Generally you don't want to be measuring .0002 tolerances in your unheated garage in North Dakota when its below zero outside. Most of the time if someone is working in a reasonably temperate situation measuring engine parts, you will be fine. If using a ring guage to verify/set your dial bore guage, the ring guage does NOT have to be the exact same size as the part you are measuring. In that perfect world situation, the best choice is a ring guage that is EXACTLY the size you want to verify...........but unless you are measuring a somewhat standard size like 2.000 its unlikely you will find a RING GUAGE that is exactly what you want. In industry, they often make custom ring guages that are the exact size as what they want the production parts to be. Generally there is a range of motion for the tool/gage you will be using. By that I mean something like a micrometer will check dimensions from say 1.0000" to 2.0000". If you have a "standard" that you use to verify the micrometer is accurate........the guage can be any known size between 1.000" and 2.000". It could be 1.3435". If you check the micrometer and it reads 1.3435", then its assumed that the micrometer will be accurate anywhere in its 1.0000 to 2.0000 range of movement. If someone had a 2.0000 ring, it could be used to verify both a 1.0000-2.0000 AND a 2.0000-3.0000 intrimik. My next suggestion is for someone new to using a micrometer. There are name brand micrometers that have been used forever and have proven their merit. There are also a lot of lesser known brands that do just fine. Don't shy away from a good buy on a set of micrometers because they aren't name brands. Just check them against the standards that they came with and see if they are accurate. Practice a little with getting a "feel" with them. I would suggest looking for a used set of "gage blocks" also called " Jo Blocks" (Johanson) . You can find them on Facebook for $100 or less. Some people want a lot more, but you can get nice ones for $100. Then you can pick a random block out and mic it and see if you/and your mic are reading/feeling correctly. I guarantee gage blocks are more accurate than your micrometer is. The thing is that you can put multiple blocks together and make different sizes and then put a scribe on them and scratch a line exactly where you want it. Or you can check the height of them with a dial indicator and then check the part you have. Here are some examples that were listed locally for $100-$125. The larger sets are better. Don't be afraid of a set that is missing a few blocks....they usually sell even more cheaply if you make an offer. You can also get gage pins which are good for checking sizes but the blocks seem to be handier for different things. These things will always be worth what you gave for them and can be resold if you want. Look also at some of the other prices for them........$300+. The key thing to remember here is that if you have a way to verify that your measuring tool is reading correctly it doesn't matter what brand name it is.
Most micrometers come with a "standard" that is used to check and or calibrate it. The ones I have snap into the micrometer case itself. My good old Lufkin 1-2" came with a standard round gauge. My good micrometers I have had to maybe calibrate one of them over the years. Gauge blocks aka Jo Blocks come in a variety of grades from laboratory down to shop floor grade. Serious shops have them sent out for cal on a regular interval. Bad blocks are either discarded or regulated for shop usage. The finish of the blocks is key to "wringing" them together when they are stacked up to use for measuring or setting up a "Cadillac" Gauge, aka a height master. They fit together on a molecular level. Damaged blocks will not wring together squarely and can damage the mating block(s). Any case of blocks I have used come with a chamois cloth to clean them before use. Gauge pins, these also come in grades. Some sets have a chamois as well. These have to be kept clean and free of dust and moisture. For accuracy, these are often calibrated and bad pins are tossed. I worked with one real old time inspector. We had sets of Deltronic pins. These are a set of nominal and plus-minus .0001 pin sets that are quite precise. https://deltronic.com/class-x-pin-gage-sets/ I saw him do this a couple of times. Someone would take a set out and put them out on a surface plate loose and he would put them back into the case in size order just by feel.
Good info Bob. Just to be clear though, I would not worry about any blocks being damaged other than something that you could see like a nick ..........for our use it is extremely rare that you can't use the blocks because of damage. In the precision world of making these blocks, they are extremely precise and other than getting rust on them, they virtually never wear out or have a problem with accuracy. Not saying there aren't companies working to such precise standards that they might find cause to reject some..............but none of us are ever gonna find one out of tolerance with our micrometers.
Outside of one being dropped on a hard floor or getting rusty, they last a long time. I have seen a stack clamped together inside a CNC mill for some half-assed set up. Nicks can be stoned out, if they still can be wringed together, they are okay. In the factory where they are made, if one block fails a test, it moves to another lesser product line where it will be deemed acceptable.
Having had experience with these engines and BSF hardware, that's a bit much for an already used set of cap bolts. For the cost of a set I would replace them- given that Austin recommend then only being tightened twice in their service life. The 998 and 1098 are long stroke engines, and if you want to be taking them to maximum RPM, that's a large amount of force on the caps when you let off the gas in gear at high engine speed. $0.02
You wring them together so you can combine 2 smaller blocks for a larger measuring standard. They are not magnetic, the surfaces are so smooth they "stick" together.
PhilA I didn’t know that rod cap screws were recommended to be changed after two tightening cycles. I did replace the bolts with some from ARP
In school we had a required machine shop course that covered most machining processes. One of the requirements was to make a set of parallel bars that in order to pass had to be wrung together My understanding is that surfaces are so precise that a vacuum is achieved and basically atmospheric pressure holds the parts together.
I guess my only questions are, is the torque wrench calibrated and certified ? Depending on the brand, some are off as new and can't hold +-5% torque, otherwise carry on !
George I didn’t resize rod ends -see above- by my somewhat crude measuring technique I believe the rods are within spec less than 0.0005 out of round Milwscruffy I haven’t had torque wrenches calibrated in a couple of years although I test two wrenches against each other. One is a Craftsman clicker type the other is an old Blackhawk beam type. They look to be within a couple of ft-lbs of each other it’s possible both are off but probably not.
ekimneirbo and others here did a great job explaining what is needed to check typical engine tolerances. RE Performance UK just did a video of the process and tools used in the shop. They do money builds and have a good rep. Adam Savage Tested also did a video a while back about measuring where he went down the rabbit hole of finer and finer tolerance.
Thats an excellent choice of words. Its hard to explain measurement because its hard to say doing something a certain way will or will not produce the correct reading. If someone is dealing with the fit between a shaft and the component surrounding it..........the amount of precision required will vary greatly depending on what that component is. We have all put "ball bearing" type bearings on shafts some time or another. The fit between the inner race of the bearing and the shaft must be a "slip" fit or even "pressed into place". That means both parts must be really really really precise or the bearing will flop around. Even a .001 can feel loose. A cranks "rod journal" is also a shaft with a component surrounding it. In this case its a bearing in the shape of a shell and it can operate just fine with maybe .003/.004 of clearance. When we install the bearing into the rod, we try to control the size of the bearing within a few .0001 th (a few ten thousandths) of an inch. A little variation when working with that .0001 scale on the micrometer is probably not going to hurt anything in the long run. Now I'm not saying it can never hurt........only that we have limited means to verify and manufacturers have made designs that are pretty consistant in size and will work often without even checking them. We can also go off on a tangent about precision and go down that proverbial "rabbit hole". We try to do the best we can within reason using somewhat common measuring tools (whatever we can afford) and then we hope for the best. Usually someone who takes the time to try and do something right has good results. I remembered this old thread and thought maybe some might enjoy seeing it again. www.jalopyjournal.com/forum/threads/worst-mechanic-ever.1243001/
Yeah, he goes into the language of this too, IIRC. It's been a while since I watched that one. RE performance also took language into account in that video. Specifically, 'blueprint' and what it means to laymen and to the people doing the work. They both touch on the affect temperature can have, something the machine shop I worked in had to deal with on some of the 'tighter' parts we made. The area ranges from 100+ with the cooler going to 60 inside with the heater going. You had to pay attention to where stuff was in the shop during the winter, because it was 10-30 outside and the heater would have localized warm and cold spots inside. Also at 60 inside, just handling the standards or measuring equipment for a while would change the results. Stuff the customer wouldn't understand in time taken to QC the work. A 'fresh' part was checked as soon as it came out of the CNC for a change from the last part at each step, but was final inspected later when it equalized with the environment. We didn't do really close stuff for the most part. 10ths (ten thousandths of an inch) was about the limit.
Man , when did this place become a scientific forum. We are contemplating precision remanufacturing. I remember an incident where I overtorqued the connecting rod bolt on my 427 to 60 ft lbs. I loosened both, retorqued it to spec, and never thought about it until now. I beat the crap out of that engine, and wound it up daily.
Is what I get out of these threads is a few points of view ie: what works ,what doesn’t work and you’ve got to be kidding me. When I posted this topic I guess I was hoping to get a majority of don’t worry run it What I got was from don’t worry run it to new bolts resize etc. What I did was put in new bolts (found out the factory suggest only two torque cycles on bolts) and I did not resize the rod big end - looks to me to be in spec and no appreciable distortion near as I can tell. For the extra $100 I spent I’ll be more confident. The engine may have been ok using old bolts maybe not. I also learned a few things. Over the years I’ve freshened a few engines beat the hell out of them with pretty good luck ,one seized after maybe 30,000 miles although it was spinning faster than a sane person should’ve been running. Oh and I do like to go down the rabbit hole - neat shit in there
As has been stated: dial bore gauge period. Many have used other methods and had good results. Why take a chance when you know there is a better method? If you work in a machine shop you will see scary results on rod crank bores over and over in regards to bolts. Even removing the originals and reinstalling them will give strange results some times. All modern rod bearings are made wide at the parting lines to compensate for cap misalignment. The whole point is to not interfear with the hydrodynamic wedge that is responsible for the oiling of the bearing.
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