Engine mount bolts

Suspect I’m covering old ground so thought someone must know. Removing front engine mount bolt can be a real pain never had an issue but many have. To me the design is from the Icarus wing design shop, I would have thought a nut either end would mean that undoing one and tightening the other you would effectively have a puller capable of generating tons of force? So out it would come? Normally threaded rod is used for light load/ shear applications however HT rod is available ( painted yellow on end ) Does anyone know the grade this is in comparison to a normal HT bolt? As they are metic coarse then the effective diameter is less 12mm possibly 10 mm but this is still a huge shear strength.

Regards Ratt

My only concern with using studding would be that the vibration from the engine could wear the engine casing where the stud passes through, the threaded steel being harder than aluminium and the thread edges sharp. If you wanted a nut at each end then why not put a thread on both ends of some solid bar? I use stainless steel engine mount bolts and they get plenty of copper slip where they pass through the engine casings, so far no problems.

PS I have an old engine mount bolt in my tool box that I use to drive the bolt out with, if it gets stiff.

Yeah - it’s an interesting one.

I think as a known issue it’s easily kept on top of. Mine gets checked and greased as a service item. Main issue is when you happen upon a neglected one.

Not that that remotely answered the question I suppose.

Thanks for reply’s yes that could be an issue, not keen on stainless as never sure if grade and the tensile strength is way lower. Agreed if they were removed regularly then not a problem but a bike bought non runner could be 10 years or more.
Will find out the grade of tensile strength of HT screwed rod in comparison. Possibly there’s a stud of the correct length.

Regards Ratt

Apparently yellow colour designates the HT grade 8.8 which is the high load structural bolt. From what I can see a 10mm bolt can take an enormous load Probably two elephants not that I have weighed many. But certainly many tons.
Personally although not shear strength I would have no issue using this as a front mount fixing and definitely prefer to stainless. This is only my opinion so not a fully investigated recommendation.
Hence the name for the bolt holding the wing on a hanglider
The Jesus bolt :thinking:

Regards Ratt

I would strongly advise against studding for engine mount bolts as they will wear the galleries through the engine case and then you may have to sleeve them. If you do not want to use stainless steel then use the standard bolts and grease them, as Butch said, as a service item.

Have to agree really, need to be plain shank through the eyelets or whatever they should be called, then only threaded on the ends but then of course that defeats the object of being able to pull them through with a nut. Even that may not work, some of the horror stories I’ve read the bolt can be so corroded in the nut will just round off or the stud end snap off. I’ve never had this problem but then I was warned early on, so I agree monitor it and keep it lubed, maybe an annual have it out for a clean up and regrease.

Hello my iPhone auto fill/ spell check doesn’t like ‘regrease’, well tough it’s staying. :smiley:

I had this problem many years ago on a Le Mans. I wasn’t even aware that it was a problem until I read about it somewhere. That was it then. Once you know about something you can’t ignore it. I checked my front engine bolt and it was solid. Over a period of weeks I tried everything. Heat, several times. I even made a channel with plasticine along the front where the bolt is exposed and left it soaking for days using some suggestions off this site. e.g. nail varnish remover and paraffin, diesel, easing oil all to no avail. I didn’t need it to come out at that time but, well, you know the feeling. The final desperate measure was to get a second hand timing cover from Reboot spares and then carefully cut through the timing cover and bolt just inside of the engine mounting points. I pulled the timing cover away and the part of the bolt passing through the frame pushed out with a finger. The centre piece was still with the timing cover when last seen.
I bought a lovely 850T about 14 months ago. Guess what I checked when I had it home. It was already well greased.
Thanks for reading this far. :relaxed:

It would be ok as you would only have to break the bond between bolt and engine casing, and then drift it out. If you made a rod threaded both ends you would then have the original bolt to use as a drift. Simplest solution is keep the original bolt well greased, you know it makes sense! :smiley:

Thanks for all the interest, fortunately I have a good mate who is MD of a heat treatment company, I thought there were 98 grades of stainless he said it’s way more than that and agrees 316 is very weak relatively. He reckons that he can get studs bolts any length so will have a stud two nuts high tensile. Years ago in industry a large nut 60mm in a recess was needed to come off. Heat, lube, everything to no avail, then we cut a deep notch and got an air chisel with a blunted end 5 mins it was off ? Why ? Something to do with the repetitive vibration. Haven’t done it but drilling end I would place a socket with a sleeve made to fit 1/2 inch square so that a 6/8 mm drill could be perfectly on centre? Yes Lub the bolt but when a barn find then. Regards Ratt

If a barn find it will not have studding so you will have to remove using other methods. I would strongly advise against using studding though as the threads will wear the gallery in the crankcase that the bolt passes through over time and with vibration. If you use non-stainless bolts an annual removal and re-greasing is all you need to do.

Another thing to do is to simply undo the nut then turn the bolt through half a revolution to make sure it isn’t seized each time you change the oil, or as often as you see fit.

Started resurrecting a T5, tried bolt turned easily noticed casting is complete ie no gap in the middle so no ingress ? Also in aircraft industry to prevent electrolytic corrosion we used ,
Yellow shit ie Duralac paste

Regards Ratt

I use that stuff on the drive box mounting bolts on my V50 now. Not sure what happens back there but I’ve had to saw swinging arms off on two separate occasions.