Rod bolt stretching

[Jay Smith]

Just a note for the interested , I always replace rod bolts on every 5/16 “ headed bolts on every motor I build I buy from Pro Marine years back I had a buddy that worked in a test lab that tested tension strength of bolts. I had him test OEM , and the Pro Marine and found the Pro was 43,000 verses 33,000 on the OEM ones , that being said here lately they send 2 different bolts I assume from different vendors one is labeled do NOT use the 30 lb torque and add the angle method the others are not labeled , I torque these with 271 added to 35 ft lbs , what I’m call to all’s attention is lately there are some that will NOT “get” to that torque value they streatch and the middle looks like chocolate 2 out of 12 were ash canned I have on hand extra new bolts to add to the new set to have a full set that will reach my torque value , I built 2 motors this week and only 2 out of 24 failed to reach the 35lb torque I require . I highly suggest buying extras to have peace of mind with this critical part..

Happy Holidays
Jay

[Dave S]

Jay... as per my response to omc cross flow bolts..... the omc bolts seemed harder JMO.....Need to Ck.

[Capt.Insane-o]

I just used a set of non tty bolts to 35 ft lbs and had no issues. Before use I always clean them with contact solvemt and they were very dirty out of the bag.

[Jay Smith]

+1
Capt ,
i always use carb cleaner on all threads before adding my chosen thread coatings .. Don’t know where folks buy rod bolts but this is just what I find with a few Pro Marine bolts I’ve witnessed ...

Jay

[H2OPERF]

That"s pretty scary.. bad or no heat treat..I worry about aftermarket companies switching vendors and wonder what the hardness testing sample rate is? 1 per batch.. never who knows.. I have noticed the omc bolts appear to have a dimple in the head like possibly each one has been hardness tested as they are made.

[Jay Smith]

I gotcha , and if your a home builder and don’t do these day in and day out like I do why would you have reason to buy extras ???? As I said this is not super common but you can buy the Pro Marine bolts packaged in 6’s and they are very reasonable priced but I buy parts like this , bearings , gaskets , spark plugs , seals , check valves , in sets enough to build 6 complete 2.5’s so if I get dinked on some part I don’t like I have extras to replace and send back for replacement, btw it not only non OEM vendors that have bad parts Mercury has had a load of junk con rod bearing that the cage had a wrong Brunel that came on 280 , drags and they also had crap cranks on same motors that had “speedy” sleeves on upper crank bearing upper ....

Jayb

[powerabout]

Jay I had it back in the day with OMC xflow bolts, I get a bad feeling when a bolt does a much larger turn to get to torque that the other 11 did. No problem at a big dealer, just grab a few more.

[Gordon02]

Jay, I plan to replace my head bolts with hardened studs and use flange nuts to secure the heads on my little 2.0L fatblock motor. This is done all the time in drag race bikes/cars where tear downs are common. Why not do it to preserve the aluminum threads on all builds? I'm still loving those ProMax heads you built for me 20 years ago! Gordon

[Jay Smith]

Hi Gordon ,
I’m not a stud fan guess I’ve had to drill too many of them out of blocks snapped off at or below deck line , I built a drag motor last week and requested customer to mail me the stock head bolts to replace studs he had installed , looked like just a hardened all thread rod with coarse threads on both ends ( not gonna get it outta my shop ) have a great Holiday Season ....
I prepare the female , male and bolt flange before installing , and apply never seeze to male thread , I never torque any more than 35 ft lbs you’ll always be good , always works for me , BTW if you do have a failure use time serts to repair bad threads they come in custom dead nut correct lengths , none of that stacking crap IMO heli coils went out with Edsels ....See ya !

Jay

[Merc 2.5]

Jay I'm not a regular builder but the 2.5 I just built ... this actually happen to me. I had all torque down gud then broke 1 and stretched another quite a bit , thought it was faulty torque wrench at 1st but now I'm 2nd guessing myself. , I replaced with all new with a new torque wrench and all was fine so I'm not sure, thanks for posting. Just sumthin to look out for when wrenching on one

[Jay Smith]

Your very welcome , if I can bring attention to a possible questionable part that can take a motor out , I build SO many of these and I see SO much the average occasional builder misses I don’t mind bringing it to the forums attention ...

Jay

[Dave S]

I know it is costly..... but why not just buy SPS bolts....... cheeper than holes in block.

[Jay Smith]

The SPS- ARP rod bolts are expensive and much stronger than the 5/16” head bolt but to get the socket on the bigger 3/8” bolt head the rod cap must be modified for needed clearance...

Good Luck ,
Jay

[Chaz]

Looking back over the half a century ... naaa , Pro never ask's for my resume or how many shade tree's on my property . I just give them my five digit dealer code and they have my credit card on file ..

Since we are throwing out the high dollar hardware ($18.00 and up) there is no need to mention the 848475 / 91995 replacements or the specs that go with them.

Which leave's a choice of three bolts for the 2.5L

All three come with simple instructions.

None of them call for 35 lbs/ft. of torque.

RB7000 replaces 93886 30 lbs/ft $2.75 ea

RB8000 replaces 763491 30 lbs/ft $3.00ea

RB8000P also replaces 763491 however it requires 30 lbs/ft plus 45* $6.00 ea

As a point of info :
The 3.0L bolts come in either a ...

RB9000 House brand 30 lbs/ft $5.00 ea

RB9000-1 Merc / Quicksilver 30 lbs/ft plus 90* 7.00 ea ( marked FC )

I bought an adjustable rod stretch gauge a few years back which also checks the beam for straightness and if the bores are parallel with each other, all in one shot.

A connecting rod vise is also pretty important. It let's you torque the caps to within a few lbs/ft or less the geometric pull to check the big end bore for concentricity and to use your ball micrometer to check bolt stretch.

I made up some tooling that makes repeatable measurement landings in the FC bolt head and tail, but honestly, the House brand parts already come with them. Just like the expensive hardware has.

Most Important: Even at my age, I've learned to follow directions ...

Chaz = thinkin, Laboratory tests prove takes pert near 60* on top of a 30 pound bolt to turn it to fudge ...

vnemous ... not one word to my Mrs ..





It's OK ... I ate the evidence ....

[Mrzip]

I Use SPS. Never Any Problem's.