Ovalled engine mount holes in block

[Roger Ford]

I've noticed that my engine mounting points on the side of the engine block seem to be a bit ovalled - presumably as a results of my recent major crash.

 

Should I worry? I'm pretty sure the bolts will still hold. I suppose properly I should get the holes welded, then redrilled and tapped, but that sounds like a major expense, and might possibly cause warping of the block. Another option would be to just drill them out and helicoil.

 

What do we think? It looks slightly worse "in real life" than it does in this pic:

 

http://www.rogerford.info/pics/enginemounts.jpg

[Jason Plato]

drill and tap bigger holes ?

[Roger Ford]

Then I'd have to modify the engine mount brackets as well, don't think you can just drill them out bigger. They're M8 at the moment, I've never heard of M9 so it would need to be M10, which is quite a lot bigger.

[mic]

Can you not helicoil them?

 

[Roger Ford]

Don't see why not. That's the option I'm currently aiming for, though I'm slightly concerned that the helicoil may not have enough grip if the hole is too wide. Probably not going to be an issue though.

 

I don't have an M8 kit, anyone know if these Neilsen ones are any good? That's a lot cheaper than a proper Helicoil kit, and the proper ones don't include the drill, which is usually something obscure like 8.3mm.

 

Edited by - Roger Ford on 8 Nov 2011 20:45:59

[mic]

They look identical to the ones I use. Should be perfect.

[millsn]

Looks to me like the bolts you have been using must have bent somewhat in the collision. I'd replace the bolts but the holes look to be shall we say 'locally chamfered'. I don't believe the hole itself is oval as such. I can't see it being an issue, most of the thread depth will be fine

[Roger Ford]

Yes, the bolts are bent and are scheduled for replacement. So perhaps I can get away with it. Turns out I do have an M8 helicoil kit, but not the required 8.3mm drill (I imagine I used 8.5 last time). I'll get one as a precaution.

[anthonym]

Toyota use M9 for calipers, as do I think some others (says google)

and my DS sump now has M7 cap head originally from Citroen as the repair was carried out in France. Known as b*st*rd sizes, not least because of supply and tools to fit.

 

Having just replaced my broken (sheered weld, an older 2000 pre update mount) LHS engine mount, I was surprised that the engine does not fall out of the car, it just leans a lot and breaks other things.

 

Helicoils (the brand): I was recently told over and again that "time serts" from I think Wurth are much better: but I know not why. Some told me the method is old fashioned and others told me it is de rigeur. So I formed my own view (no space here for that).

 

How about a 3/8 cap head bolt?

 

edit: btw I agree with noet, that was my first thought, but didn't think of the test idea, I was thinking if the bolts screw in easily with fingers the depth of thread will be apparent as well as firmness or lack of.

 

 

Edited by - anthonym on 9 Nov 2011 11:01:18

[noet]

If the treads are fine inside from the damaged outer treads and new bolts enter properly, I would not do anything. You will probably just loose 2-3mm treads, but still have enough hold. You could try with a torque wrench to messure sufficient hold.

[CharlesElliott]

Oval holes? You don't want to worry about that - the whole thing needs a good clean first.

 

So what's the plan - you drill out and helicoil with the same thread as originally there? Wont that mean the the 'enlargement' at entry will still be there? I guess I'm a little confused as to how the helicoil approach will fix the problem.

[CharlesElliott]

Also, I have some capheads for these mountings if you need new bolts.

[rj]

Anthony,

 

 

The Würth thingy is a proper bushing whereas the Helicoil is a spring-like insert. IMO the first presents the best thread to work on from.

[Sheds Moderator]

Inspect threads, if still sound attach as normal. If damaged, Helicoil.

 

Charles - Helicoil works because for an M8 the original (female) thread has a drilling diameter of (say) 7mm. You then tap it so the outer ends of the threads are (say) 8mm (actually a bit bigger). Your male fastener has a major (outer) diameter of 8mm. Great. Now if you damage this the helicoil requires a drilling of 8.3mm (see above) and in 99% of cases this takes in any damage. Then wind in your insert, job done.

[Roger Ford]

D'oh, it's M10 not M8. I tried screwing a bolt into the bottom one and it's quite loose. I need to do something.

 

McMillan suggested fitting some studs in there with some chemical metal to lock them in place and fill the gap - then instead of using bolts to fix the mount, you fit it over the studs and attach it with nuts. Makes sense if I can find some suitable studs.

[anthonym]

Now we know it's M10 it looks to me like you could go straight to M12 and have sufficient metal left. Would be a good question for a CC engineer, only a phone call away.

 

Also wonder how deep are the bolt holes and threads? If you use longer M10 is there useful thread length deeper inside? If you have 20mm bolts you won't be able to tell what is beyond with those. Stick a piece of wire in and compare, then try a longer bolt to check biting thread depth.

 

M10 25mm long, per my notes with a CC engineer ten days ago. Sorry, completely forgot I had had that conversation. Further check in parts online says 10mm x 20mm http://www.caterhamparts.co.uk/product.php?id_product=3310 Assuming S3 . Looks to me like 1.5 thread

 

M11 ? or M12... let's see: M11 x 1.50 9.7mm drill, so how wide is an M10 hole? Or what is the next possible tap size?

 

food for thought http://bobmay.astronomy.net/misc/drillchart.htm ? Start reading from 10mm presumably.

 

 

Getting a spanner on to the reversed nuts/threads idea would be hell on Earth with the engine in situ - at least on my S3 it would. Especially with the current updated DS LHS mount where the forward of the two is even more difficult, which I did not think possible. Not sure what you have - and hope you are totally ok after the accident.

 

 

After a great deal of thinking about this, I'd prefer M12 (cap head) if possible, for such a critical part. If possible. For all sorts of reasons. Having just replaced my own sheered mount.

 

Edited by - anthonym on 9 Nov 2011 23:17:44

[Roger Ford]

Better pic after cleaning it (not up to your standards, of course, Charles 😶‍🌫️)

 

You can clearly see the casing is slightly cracked and the hole quite oval.

 

http://www.rogerford.org.uk/pics/enginemounts2.jpg

[anthonym]

ugh. that looks more like a cracked thread. My example on my DS base broke off from the block, the repair was the M7 bolts up from M5, also longer and deeper also loctite. To compensate for the outer crust degradation. Given the engine leans in to this, rather than pulling on it. Would be nice to get an engineer's view though. Expect one will be along momentarily. I reckon 25mm M12 if possible plus liquid metal maybe, so wait to see the received wisdom.

 

Edited by - anthonym on 9 Nov 2011 23:28:07

[Roger Ford]

Anthony, unless I'm looking at the wrong bolt it's M10x35. I'll measure the depth of the hole. And yes, it's coarse thread (1.5mm).

 

McMillan actually suggested fitting the mount to the engine before putting the engine in - which would mean no grief doing the mount up, but might make it a little harder to get the engine in.

[anthonym]

35mm sounds like the ones that drop down through the mount bushes... but they aren't cap heads... leastwise mine aren't.

eidt: time I asked which side of the engine this is and type etc? I might be imagining the wrong mounting 😳

 

Regarding access I was thinking you might want to spanner check the mountings which would be .. not easy.

 

Edited by - anthonym on 9 Nov 2011 23:38:39

[Roger Ford]

K-series, LH side. Close to the alternator.

[Sheds Moderator]

Drill and Helicoil for me. Yes, it's damaged, but a HC will take it back to good metal. Your ghetto repair is to epoxy a stud in there and mount the engine, then secure it with a nut, assuming you can get access. The latter approach is irreversible without drilling and considerable aggro, but you don't remove your engine every week and OK, it will be a bit fiddly, but that's not life threatening.

 

If it's too bad to helicoil your next best engineering repair is to fit a threaded insert in the original size, there is plenty of metal.

[anthonym]

battered what's the difference between a helicoil and a threaded insert? I was thinking they are the same thing (obviously not).

 

Roger DS Apollo? i.e. oil hoses get in the way beneath/next to alternator and LHS engine mount bolt (at least one of the two).

 

edit: judging from your RHS Wanted post, you don't have DS, but Apollo? I am asking because of the effect on access to the bolts.

 

Edited by - anthonym on 10 Nov 2011 20:06:18

[Sheds Moderator]

They both do the same job but slightly differently. A helicoil looks like a spring. Google it for a pic. You drill a hole slightly oversize, then using a special tool you wind in the insert. The middle of the helicoil is obviously threaded to accepta screw of that size. The helicoil bears directly on the screw and upon the parent metal, rather like a Rawlplug in a wall. A threaded insert in contrast is a machined block of metal. It has a proper external thread and a proper internal thread. Imagine if you will a big bolt which you have centre-drilled and tapped so it will accept a smaller screw or bolt. If you then drill out the parent metal to accept the bigger bolt, wind it in and then chop it off flush, the smaller threaded hole in the middle will accept the original screw size. You can, if you wish, secure the insert with adhesive. This is obviously a permanent repair and stronger than the original if used in aluminium.

[anthonym]

impressive, so why do "we" even discuss helicoils (etc) when threaded inserts are made of sterner stuff?

 

edit: I think I have been seeing both as the same thing; will now pay more attention this evening.

 

and thanks.

 

Edited by - anthonym on 10 Nov 2011 20:08:05