Author Topic: Broken bolt oil pan (Read 4109 times)

The Gurg · « **on:** October 15, 2019, 11:02:45 pm »

Rebuilding a cb750 K5. Had two bolts break off bolting the oil pan back on. No issues getting either bolt out. Torque wrench set to 96 inch pounds. There were no washers on the oil pan since I’ve owned the bike, but I’m seeing washers on the parts diagram. The diagram I’m looking at doesn’t always have the parts right with all the changes they made over the years of production. I’m assuming washer were on every year? Thinking that without the washers the bolts were bottoming out and breaking. Bought new bolts and washers for the entire pan. Two of the bolts are longer and different (I did have them in the correct spots when they broke). I measure all the bolts and compared to a parts list to make sure they are the correct length and they all were. Anything else I should check or am I good to go? Got the new washers in today and they seem so thin to make a difference.

RAFster122s · « **Reply #1 on:** October 15, 2019, 11:15:37 pm »

Uh, why are you trying to torque an oil pan bolt? Sounds like you need a quality torque wrench and need some training on hand tightening a bolt to rough torque values. 15 ft lbs of torque on a fastener is usually achieved one a fastener is threaded in until it stops with very very light force and then turn the fastener 1 flat of the fastener head farther.
A small bolt like an oil pan bolt I would hand tighten with a wrench and not reach for a torque wrench, anything inside the motor I would be more concerned with torquing to spec. A brake caliper bolt I would torque to spec...
Check the depth of the two bolt holes that broke and possibly run a bottoming tap into the case holes there to clean out anything on the threads. Als, before running the tap in, ensure the hole doesn’t have debris in it causing the bolt to break.
The washers have a added benefit of spreading the pressure from the fastener to a larger area.

disco · « **Reply #2 on:** October 16, 2019, 01:16:45 am »

Not sure of exact technical name, but pretty sure the original bolts for the oil pan are those type with the washer “built-in” to the hex head.

chrisbc55 · « **Reply #3 on:** October 16, 2019, 03:08:26 am »

They are all “flange bolts”

ekpent · « **Reply #4 on:** October 16, 2019, 05:13:21 am »

Yep no washers and use the torque wrench for head bolts/nuts and other internal stuff. Anything with a gasket is easier and safer to just tighten by hand. Be careful of the bolts around the cam towers as they strip out easily also.

The Gurg · « **Reply #5 on:** October 16, 2019, 07:54:11 am »

Not wanting a debate, just wanting understanding: why are there torque values if you don’t torque to spec on the pan? I can understand if you are moving fast and experienced, that you don’t need to, but if your inexperienced like me I thought using a torque wrench on non-internal motor parts was like training wheels on a bicycle?

I watched a hackaweek video right before this happened, where he takes a click torque wrench and tightens them right up to 96 inch pounds with no issues. I do it and it breaks. Trying to understand why. I didn’t go back for a second pass or anything. Just never got a click, but did on several other fasteners on the pan. I did brush motor oil on the threads and then wipe it off with a paper towel before starting. I know oiled fasteners is a debate in the mechanic community.

Also, why no washers? I can understand that maybe I don’t need them. But do they harm anything? Which year used washers?

The torque wrench I’m using is a Craftsman 9-31423 25-250 in.lbs 3/8" Drive Microtork Torque Wrench. I know that Craftsman isn’t what it once was. But I wouldn’t think of a $70 wrench as completely worthless.

I have a 6mm bottoming tap, but both breaks were outside of the engine case, close to the head of the bolt. I used a small pen light and inspected the threads and holes. They look great, so I’m not going to run the tap.

RAFster122s · « **Reply #6 on:** October 16, 2019, 08:04:16 am »

Oiled fasteners require lower torque specs and a oiled bolt will torque to a higher setting with the wrench set to a lower value. I do not recall how much exactly the reduction value is, I would need to look it up.
The flanged bolt has the washer built in...

The Gurg · « **Reply #7 on:** October 16, 2019, 08:56:39 am »

Ok, so you think the error was oiled hardware with unadjusted torque values?

From what I’m reading flange bolts and washers have similar function but not identical. But yeah you’re right about a flange bolt essentially being both combined.

If I added the washer wouldn’t that make it so the hole would be slightly deeper and less likely to bottom out?

What does “one flat of the fastener head” mean? Sound like that would be a half turn or 180 degrees?

PeWe · « **Reply #8 on:** October 16, 2019, 09:14:38 am »

It's easier with a good torque wrench.
I use a 1/4" socket model for 2.5-25Nm. Perfect for these small M6 screws.
Oil pan 7.5Nm, retighten after a while when using new gasket.

All other covers same value. I have tightened valve cover by 5Nm, retightened a few hours later. No leaks.

Honda torque numbers are high for M6. I tighten less to avoid stripped threads. Head nuts however, can be tightened more.

I have removed oil pan several times reusing the old but not old by years. Honda engine cover gaskets work fine to remove cover and use the old gasket again.

The Gurg · « **Reply #9 on:** October 16, 2019, 09:41:12 am »

Anyone have a recommendation for a good 1/4 drive inch pound torque wrench? Preferably something I can pick up rather than have shipped.

calj737 · « **Reply #10 on:** October 16, 2019, 10:28:07 am »

Your bolts sheared because the bolt was weakened due to age and corrosion. Use any decent 1/4” drive torque wrench and you’ll be fine. Oiled or not, it won’t make a difference at 8# of torque.

PeWe · « **Reply #11 on:** October 16, 2019, 11:37:38 am »

I use this model

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.de%2Fulk%2Fitm%2F174055150847

I have a 1/2" socket, 10-60Nm of same brand, Hazet.

RAFster122s · « **Reply #12 on:** October 16, 2019, 12:55:44 pm »

The head of a fastener’s sides are referred to as “flats”. So, turning the bolt one flat is moving the flat side one “flat” tighter or looser.

The Gurg · « **Reply #13 on:** October 16, 2019, 03:55:40 pm »

Thanks for the flats explanation, RAF122S!

Thanks everyone for taking to comment!

I spent some time trying to find someone who would calibrate a torque wrench in Nashville, to no avail. Snap On and Mac Tools do but you have to have one of their $350 wrenches.

Have new bolts and I think I’ll throw the washers on. Can’t hurt, right?

Probably torque per RAF122S instruction, and order a new inch pound wrench for later on.

Always appreciate PeWe suggestions! I’ll have to look into whether I can get that wrench is the US.

maxheadflow · « **Reply #14 on:** October 16, 2019, 06:54:08 pm »

A good place to look at generic torque figures is here..

https://www.futek.com/bolttorque/metric

I would not go much more than 72 in-lbs.

RAFster122s · « **Reply #15 on:** October 16, 2019, 10:17:53 pm »

In the case of 8 lb ft of torque you would turn it 1/2 a flat past full contact. Not a lot of torque. The size of spinners/wrenches correspond to the torque value for the fasteners, smaller fasteners require less force so the wrench is shorter so you won’t be tempted to crank on it, less of a lever to transfer the force...

Kelly E · « **Reply #16 on:** October 17, 2019, 06:20:31 am »

I use a skinny WWII vintage Plumb 1/4" drive 6" extension on all the small bolts going into aluminium. It works like a torque stick. It will only tighten a bolt so much before the extension starts to twist under load. I have never stripped a thread out since I started using it. It has no finish left on it and was rusty when I got it from a pawn shop with a bunch of rusty Plumb wrenches that turned out to be from WWII.

754 · « **Reply #17 on:** October 17, 2019, 09:16:41 pm »

I doubt the proper Honda bolt would give you these problems.
Someone should have a used set.

BPellerine · « **Reply #18 on:** October 18, 2019, 05:16:43 am »

if you are looking at a parts diagram that is from a ko you will see washers,later bikes used flange bolts.

The Gurg · « **Reply #19 on:** October 18, 2019, 08:33:13 am »

Caught the snap on truck and he tested the craftsman inch pound wrench. It’s reading 20% off. Probably my fault (and not Craftsman) for not storing the wrench on the lowest setting during the rebuild. So far torqued up the shifter assembly (with Loctite) and primary chain tensioner. The case is combined with threebond. All the case bolt were tightened with my cobalt which is spot on. Any reason to go back if everything got torqued to 9.5 foot pounds instead of 8? Or should it be fine?

I bought a snap on inch pound wrench. Between that and new Honda bolts, any issues should be gone.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #20 on:** October 18, 2019, 08:51:37 am »

Get a 1/4" torque wrench. IMO you will snap off more using a 3/8" torque wrench whether 8# is 8# or not on both wrenches. Save the 3/8" for the bigger stuff.

maxheadflow · « **Reply #21 on:** October 18, 2019, 09:16:22 am »

Quote from: The Gurg on October 18, 2019, 08:33:13 am

Caught the snap on truck and he tested the craftsman inch pound wrench. It’s reading 20% off. Probably my fault (and not Craftsman) for not storing the wrench on the lowest setting during the rebuild. So far torqued up the shifter assembly (with Loctite) and primary chain tensioner. The case is combined with threebond. All the case bolt were tightened with my cobalt which is spot on. Any reason to go back if everything got torqued to 9.5 foot pounds instead of 8? Or should it be fine?

I bought a snap on inch pound wrench. Between that and new Honda bolts, any issues should be gone.

Was it 20% high or low. Leaving the wrench set to some value can cause the spring to sack out and read low. I wouldn't tq more than 7.5 ft lbs.

The Gurg · « **Reply #22 on:** October 18, 2019, 11:40:34 am »

I did buy a 3/8 drive inch pound snap on wrench, he didn’t have a 1/4 drive on hand.

The wrench was clicking 20% lower, so everything got torqued 20% higher. The 8 foot pound fasteners were torqued to 9.5 foot pounds because of that discrepancy. I’d have to split the case back open to address the primary chain tensioner.

calj737 · « **Reply #23 on:** October 18, 2019, 12:28:08 pm »

You're fine. Go forward.

The Gurg · « **Reply #24 on:** October 18, 2019, 01:18:43 pm »

Ok awesome, on pressing forward, just wanted to make sure I wasn’t being lazy!

As far as the wrench, I just picked it up today. I have 30 days to swap it for the 1/4 drive. I know 3/8 is more versatile, but 1/4 will have less issues over torquing and higher accuracy. Should I go through the effort of swapping it?

The Snap-on is the QD2R200. The calibration certificate says it’s accurate to within 1% at 40 inch pounds. Even more accurate at higher amounts.

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Author Topic: Broken bolt oil pan (Read 4109 times)