connection rod bolt question

frank edwards · 08-26-2020, 01:29 PM

hi guys,i am in the process of rebuilding my engine and at the piont of installing con rods to cranckshaft.the rod bolts i recieved from pelican are listed as 914-103-171-01-m260. the porsche part is listed as 914-103-171-01-oem,so look compatible ,but the new bolts are plus 5 thou on the neck and will not push fit into cap any advice.thank in advance stay safe,frank

Flat6pac · 08-26-2020, 04:46 PM

Rod bolts don’t just fall in, they usually need to be supported and tapped in to seat.
Lots of times they need to be tapped out.
Bruce

frank edwards · 08-26-2020, 07:03 PM

thanks for the info bruce the bolts i removed were a nice solid fit but stretched 10 thou,so wondering if torque to specs will stre:ch bolt and reduce dia.just like chewing gum,ha.

ahh911 · 07:33 PM

Hi Frank. Same thing, same bolts. I wasn't going to hammer the daylights out of them, took a drill press, protected threads, sanded them down (still have to hammer then in though, but they are snug). Brutal affair, then figuring out the torque will be (very) painful. I'd get something else in retrospect. See attached link where I got these down to size, but I'm still living the 20Nm+90 vs 55Nm. ARP it, I'm in canada (ARP to here 500$ Can delivered taxes in)and I had extra of the bolts you have, so I stuck with it, besides arp tech spec'd the bolts as I wrote in the attached link and they would not have been snug at minimum tolerance they can guarantee, those min tolerance bolts would have fallen through so he suggested I use the bolts I had, so it's up to you, you can call them yourself and see. Anyhow, looks like I'm going 20Nm+90, but I called Porsche today and they called back, saying 20Nm then 55Nm, just like the original spec, this crazy torque stuff will waste your time/energy/vacation. Unless you are retired or have months to kill or are a go-lucky sort of guy, get the arp and tell us how it went, it should work out just fine, it's just that the cost here and the uncertainty of receiving a min tolerance delivery from ARP and they would not cover me if that occured meant I had to stay the course.

Phil

Rod bolt diameter New vs Orig and Junction

stownsen914 · 08-27-2020, 03:33 AM

The bolt is + .005" at the fat part? Is that compared to the old bolts, or compared to the rod bolt hole they need to go into?

The fat part of the bolt isn't going to stretch and become narrower from torqueing.

frank edwards · 08-27-2020, 01:14 PM

many thanks to all your replies and suggestions,it would be nice if the company that manufactures these bolts gave us some guidence,so we didnt have to go the trial and error route,this is what i am doing, im going to try one rod by torqueing useing new bolts to 5-5.5 kgm and see if it pulls bolt through,and measure stretch,also may consider old bolts maybe old porsche bolts better than new oem bolts.i will post results when i finish con rod installation thanks again all great input,frank

frank edwards · 08-27-2020, 01:22 PM

the new rod bolt is + 5 th. compared to the old bolts,hole is 3-4 thou. difference .what do you think about freezing bolt and heating rod and cap.when equalized temp will something give

best frank

ahh911 · 04:10 PM

HI Frank,
I don't want to interfere in your thought/decision process too much, but today I testfit the rods for roundness with the bolts that I worked down to only several 1/10 of a thousands more than the bore and while torquing not to the full 20Nm+90Deg that I plan on going, but just 20Nm to 55Nm i could feel at around 45Nm the bolt resistance had changed characterisitcs on two of the twelve bolts and then came back as though the thread resistance had changed as the bolts were torqued for the first time and there is the coating still on them I guess, or it seemed that the halves were being pulled up nice and tight and overcomming the friction of the fat part of the bolt (I already had the tangs pretty much lined up to stop position so it wasn't that, and the bolt returned exactly to the original free length when finished,so not stretched and like I said the bolt kept torquing up). What I'm saying is that if you have too much binding when using the expansion/contraction method to get the bolt in because the bolts are so much fatter than the originals, will you run the risk of the bolt binding up and giving false torque values? There will be a certain point where if you use the cold/hot expansion method that the bolt will have considerable friction with the bore. The 4 Thou you say larger than bore I think is very large in my opinion, I also wonder where the extra metal goes once everything return to the same temperature. Anyhow, I checked rod big end bore diameter with the bolts I spun and sanded down, roundness was near perfect at 90, +/-45 and +/-20 degrees from parting lines, thankfully, because when I worked the bolt down I used strips of varying sandpaper held like a belt, but I was still worried that maybe the bolt fat part had been made oval through my work because the bolts run on the drill press don't always spin true, that doesn't seem to be the case. I'm pretty good at using a cleaned/deburred telescopic gauge now (that takes a night to sleep on), I'd say around .005mm, roundness was around in that order, perhaps slightly more, but I guess it shows the method of sanding down the fat part does seem to work. One more thing, the little holes on both sides of the bolts that I thought you could use a lathe on are no good, they are not centred most of the time. But like I said earlier what a pain, call the arp guys? unless you don't mind the work.

Phil

frank edwards · 08-29-2020, 06:55 PM

hi phil,thanks for the reply to my problem with rod bolts.i tried two of the new bolts and torqued to 5.5 mkp about 35 lbs,hot/cold got bolt into rod.but cap didnt seat correctly on so not happy with crush on bearing i decided old porsche quality bolts better than new oem,but used new nuts,salvaged something anyway,everything went smooth, thanks again for the info and advice most welcom,best,frank