The International Cessna 170 Association

Question regarding thru bolt 537465 (corrected). Attached is a pic of my right front engine mount. While conducting oil leak mitigation my thru bolt snapped under far less than 400 inch pounds of torque. Bolt that snapped is circled. The bolt that was installed on my block does not appear to be the item depicted as compared to the X30014 Illustrated Parts Manual Figure 2 Item 12. Mine was a long bolt, it was not threaded on both sides. Are your front mounts set up similarly or do (did) I have the completely wrong thru bolt in my block?

Thanks folks! Hope to meet some of you at EAA 2022 - Wisconsin is my home state.
Miles

Miles, I've rebuilt 2, 0-300s and a C-85. I work on larger TCM and Lycoming engines daily. No, I haven't seen every type of thru (or through) bolt, and I've slept a night or two since viewing a 0-300. The circled bolt does not look like any thru bolt I've ever installed or retorqued. I'd lean very heavily in the direction that is definitely not a thru bolt.

skifast13 wrote:Question regarding thru bolt 537466. Attached is a pic of my right front engine mount. While conducting oil leak mitigation my thru bolt snapped under far less than 400 inch pounds of torque. Bolt that snapped is circled. The bolt that was installed on my block does not appear to be the item depicted as compared to the X30014 Illustrated Parts Manual Figure 2 Item 12. Mine was a long bolt, it was not threaded on both sides. Are your front mounts set up similarly or do (did) I have the completely wrong thru bolt in my block?

Thanks folks! Hope to meet some of you at EAA 2022 - Wisconsin is my home state.

IMG_1124.jpg

Miles

(I believe you’ve inadvertently made a “typo”…. I believe you meant PN 537465…..which is item 12, Fig 2. And, No…that doesn’t look right at all.
I sent you a PM earlier about a picture before I saw this post. I’d like to see the rest of that incorrect bolt, and expecially a close-up of where it snapped.
(and per the PM, the addt’l info also, pls.)

You’re absolutely correct, George, I meant to type 537465. I’ll provide the requested info after this wknd. We’re hosting NYE so won’t be able to get to hangar until next week.

IIRC, at least some if not all of the through bolts have provisions for o-rings near the case split, which if true, the case needs to be apart for proper installation of the o-rings. I have heard of some success with putting o-rings under the nuts at the outboard ends of the bolts to correct oil leaks.

Excuse me if you already know this, but be sure to torque BOTH ends of all through bolts when installing them.

cessna170bdriver wrote:…

Excuse me if you already know this, but be sure to torque BOTH ends of all through bolts when installing them.

Miles Bowen makes an excellent point…and I’ll add that twisting/torque-ing one side at a time has its’ hazards…. It can pull the bolt off-center and dislodge that O-ring (on Through-bolts which have O-rings, of course)…. and it’s a good technique to keep a wrench on the opposite end of the thru-bolt to prevent that shift while torque-ing.
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Aaannnddd…. before we get to jumping too far to conclusions…. there may be a superceded part involved here… I’m researching it now…but so-far it may be that the lower/forward fastener actually is a bolt with a head on one end…and drilled for a cross-pin on the other end. I’ve got a call into one of our Members who has recently been into this to see what we can discover.

Ok, after doing some research it appears the Illustrated Parts Catalog “depictions” of certain parts is INcorrect.

It seems the thru-bolt being discussed, which inserts thru the lower/front of the engine mount bracket is actually a “headed” bolt…with a threaded-end for a nut being cross-drilled for a pin (split pit/cotter). There is an O-ring at EACH end beneath the head and nut to restrict oil seepage.

The PN is 537465.

Miles, it also appears you do not have to split your engine to make this repair. You should be able to drive out any remaining parts of the thru-bolt…and replace it with another.

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