1986 Daihatsu Skywing - Replacing/Substituting a cam sprocket bolt

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Mon 24 Jul 2023 04:21
1986 Daihatsu Skywing - Replacing/Substituting a cam sprocket bolt - edlithgow

I need to replace a lost cam sprocket bolt.

I’d guess I probably lost it when I was turning the car upside down looking for the tensioner spring that I apparently didn’t need (I now think I can tension that manually) ironic idiocy stylee.

The bolt appears to be unobtainium as a specific car part, but its, like, a bolt, so there might be some hope of sourcing a high grade flange bolt and thick washer that would do the job.

CB20 manual shows the torque range for 8mm diam 7T (apparently JIS or Japanese Industrial Standard, which is almost but not quite the same as ISO metric. Heads are smaller and they have their own tensile strength grades. But I HOPE and believe the threads are the same) bolts to be 14.5-21.7 ft lbs, whereas the cam bolt is 21.7-32.5. This seems to suggest that the cam bolt is some higher grade than those listed in the standard table, which only goes to 7T.

This table gives torque values for ISO metric bolts

https://www.fastenermart.com/files/metric_tighten_torques.pdf

For a fine M8 of Property Class (grade) 12.9 (the highest Metric Grade listed) tabulated torque is 33 ft lbs, the same as the specified upper limit torque for the cam bolt
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After A LOT of poking around, I found this table of JIS and ISO metric strength equivalents

ttps://forums.ninja250.org/posting.php?mode=topicreview&t=88348&tro=1

JIS mark----------------------ISO metric mark
4 or 4T---------------------------4.6~4.8
5 or 5T---------------------------5.6~5.8
6 or 6T------------------------------6.8
7 or 7T------------------------------8.8
8 or 8T------------------------------8.8
10 or 10T--------------------------10.9

This suggests that 10T /10.9 may be the highest JIS grade. According to the above table, tabulated torque for an M8 fine thread 10.9 class bolt is only 28 ft-lb, less than that specified for the cam sprocket bolt, so if that is what it is, it seems it would be a bit marginal for the job.

This paper describes the development of high strength steels by Nippon Steel, and confirms that, post 1967 until their introduction in 1999, 10T was the highest grade available, due to concerns over hydrogen embrittlement and delayed fracture of higher strength steels.

nipponsteel.com n9714.pdf

(Any DIY job in Taiwan has the lurking potential to turn into an industrial archaeology thesis. I just want a bolt)

So, though uncertain as to what these bolts are, or could be, actually made of, best bet would seem to be to try and get an ISO metric 12.9 grade flange head bolt that’ll fit. I can perhaps take a silicone impression of the thread from the blind hole in the end of the camshaft.

I havn’t managed to lose the crank pulley bolt yet, which MAY be a larger version of the cam bolt (visually it looked like one as far as I can remember) with a flange on the head and a similarly super-thick washer.

I could take this around the bolt emporia as a pattern, though that might cause more confusion than its worth.

Trick is finding a good bolt boutique, a good trick if you can do it.

Or there is the Internyet

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Mon 24 Jul 2023 09:27
1986 Daihatsu Skywing - Replacing/Substituting a cam sprocket bolt - craig-pd130

There's this company in the UK: www.accu.co.uk/ which specialises in fasteners.

If you use a dab of threadlock when installing the bolt I should think it would stay put.

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Tue 25 Jul 2023 12:12
1986 Daihatsu Skywing - Replacing/Substituting a cam sprocket bolt - Mino

It's likely to be a metric fine pitch bolt. If you can find another bolt on the car that fits the recess then you can count the threads per cm and work out what the pitch is.

Then find a high tensile bolt with the same pitch.

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Wed 26 Jul 2023 00:12
1986 Daihatsu Skywing - Replacing/Substituting a cam sprocket bolt - edlithgow

It's likely to be a metric fine pitch bolt. If you can find another bolt on the car that fits the recess then you can count the threads per cm and work out what the pitch is.

Then find a high tensile bolt with the same pitch.

Thanks

I THINK the original is more likely to have been JIS, unless that isn't strong enough, in which case I suppose they might have mixed ISO metric and JIS on the same car.

I took an RTV impression of the blind hole in the end of the camshaft, using half a small tongue depressor. This worked quite well, Threaded section is 20mm long, with the last 6mm of the hole unthreaded, which is useful to know.

Found a 10mm bolt (I miss measured the hole as 8mm, The extra thickness ameliorates the concern over strength) that threads in. Wrong length, with a shank (THINK the original was all threaded), and markings that I can't interpret, but I can use it as a pattern when bolt-buying .

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Wed 26 Jul 2023 09:17
1986 Daihatsu Skywing - Replacing/Substituting a cam sprocket bolt - bathtub tom

I understand the threads for JIS are metric. The difference is the head for bolts and machine screws and the slots for cross-head screws.

Incidentally, I was taught a bolt has a plain section below the head and a machine screw is threaded the entire length.

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Wed 26 Jul 2023 14:02
1986 Daihatsu Skywing - Replacing/Substituting a cam sprocket bolt - edlithgow

Yes, thats why I thought I could probably replace with (perhaps stronger) ISO metric.

Re bolt V. machine screw, I was vaguely aware of that "strictly speaking" formal definition (I think James May mentioned it, though I can't remember if it was in one of his solo shows or if it was accompanied by eye rolling from the other two), but I think its a distinction often honoured in the breach.

The workshop manuals I have, for example, and IIRC, refer to it as a bolt.

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Wed 2 Aug 2023 03:53
1986 Daihatsu Skywing - Replacing/Substituting a cam sprocket bolt - edlithgow

Well, this is embarrassing.

After dragging inside the sills with a magnet, found the original. Safe place syndrome.

Bolt head has two pips in line. According to this Toyota repair manual (I assume the bolt isnt manufacturer-specific)

supras.org.nz/techinfo/TSRM/25_B.pdf

thats a JIS 6T , equivalent to ISO metric 6.8.

That strength class isn't in the torque table above. Perhaps one is supposed to interpolate?

www.metric-bolt-torque.com/metric-thread/metric-th.../

has it as 27 ft-lbs. That table is coa*** (the opposite of fine. Nothing to do with ones sit-upon, Mrs Whitehouse) thread only, and they can't spell strength. but on paper, as suspected, the original bolt looks to be under-strength for its specified torque.

I'm going to use it anyway, because

(a) its the original, and I get enough "you think you know more than the manufacturer" flak as it is


(b) there isn't clearance to get my torque wrench on it in situ anyway, so all this agonising over torque values is a bit moot.

Thought of improvising with my GF's luggage scale, as per here

www.engineeringtoolbox.com/torque-wrench-luggage-s...l

but the luggage scale, being digital, is bust.

I should perhaps have torqued it before I put the head back on, but I'm not taking the head off again for this

Torque is overrated anyway.

Edited by edlithgow on 02/08/2023 at 04:16

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Wed 2 Aug 2023 06:53
I very much feel that your science is very useful to me. - gbws

I very much feel that your science is very useful to me.

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Wed 2 Aug 2023 07:41
I very much feel that your science is very useful to me. - Bolt

I very much feel that your science is very useful to me.

If nothing else it keeps the brain working even if it takes a while to finish a job, keep up the good work ed :-)

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Wed 2 Aug 2023 14:23
I very much feel that your science is very useful to me. - edlithgow

How come this is now the subject, rather than just the text of a post?

Bit weird.

Anyway, I pretty much feel some sarcasm is understandable here, though I dunno if its useful.

Clearly this isn't "science", just a (more or less unsuccessful ) attempt to use the technical reference resources of the Internyet on a problem that probably isnt relevant to anyone else.

OTOH, if one got some springs and/or bits of bungee and calibrated them with weights, one might be able to improvise a fairly versatile (if a bit cumbersome/primitive) torque wrenching capability at very little cost....hmm

Not really science either, more punk technology.

.

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Wed 2 Aug 2023 14:42
I very much feel that your science is very useful to me. - edlithgow

Turns out I did have to take the head off again, because (against my better judgement) I followed the manual's suggestion and attempted to lock the camshaft with a screwdriver. This was quite obviously never going to work, and sho nuf the cam sprocket shifted and jammed.

Dont seem to have bent the valves, since I can turn the camshaft with the head off. I still cant torque it though, since although I can get the torque wrench on it, I still dont have any way of locking it, and its harder to deal with wobbling around on the car roof.

Put the head back on. Might try lashings, or maybe securing it with an old cambelt.

I'm quite impressed by the utter b******s in the manual in this context. The suggestions for locking the crankshaft were similarly reality defying.

Edited by edlithgow on 02/08/2023 at 14:48

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Wed 2 Aug 2023 16:33
I very much feel that your science is very useful to me. - edlithgow

Seems its not just me.

Yon Hubnut geezer seems to have a lot of trouble with unlockable Daihatsu timing stuff, and he has resources I can only dream of.

www.youtube.com/watch?v=imZz85ToqZ4

Edited by edlithgow on 02/08/2023 at 16:34

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Wed 2 Aug 2023 22:37
I very much feel that your science is very useful to me. - bathtub tom

ed, as you've managed without this car for so long, would it not be sufficient to put some thread locking compound on this bolt (if you can get the stuff there)?

As I've already said, I expect you to launch a spark plug into orbit (although I hope you don't), because I expect the Chinese seeing it will take it as an excuse to invade.

As you've done without the car for so long, would it be easier to buy another?

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Wed 2 Aug 2023 23:08
I very much feel that your science is very useful to me. - edlithgow

I very much feel that your science is very useful to me

(Sorry, Couldn't resist)

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Thu 3 Aug 2023 00:12
I very much feel that your science is very useful to me. - edlithgow

Clearly I'm not a "The torque settings in the manual are Holy Writ" fundamentalist (They seem to be mostly Americans) but I'm not sure thread locker is a complete substitute for torque.

The clamping force might, for example, affect the shear on the Woodruff key.

GF found me a Taiwan source of Red Loctite via the Internyet a few years ago (its on the oil pump drive sprocket) but I lost that bottle when the University got rid of the shared break-room fridge.

I can get a local "Mystical" brand a short train ride away but it might well be dodgy.

Theres also the question of possible disassembly difficulties. It might be difficult to get enough heat on that bolt, and I havn't seen the blue Loctite (or equivalent) here AFAIK.

I sometimes use thin polythene sheet on threads for a "nylock" effect, but I hesitate to apply that improvisation to a bolt this critical

Edited by edlithgow on 03/08/2023 at 00:38

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Thu 3 Aug 2023 05:32
I very much feel that your science is very useful to me. - edlithgow
Further to the above, Im thinking

(A) applying a locking compound to the head flange and washer rather than the threads might be an acceptable compromise, since it will there be more accessible to heat and/or solvents to aid removal, but still tend to prevent rotation.

(B) Superglue might do. Probably wouldnt withstand so much heat, but may be good enough for the cam bolt, which is in a relatively cool part of the engine.

Ill see if I can find some numbers
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Thu 3 Aug 2023 11:06
I very much feel that your science is very useful to me. - edlithgow

www.jstor.org/stable/44548233

J.A. McGeehan, J.P. Graham and E.S. Yamaguchi

SAE Transactions

Vol. 99, Section 3: JOURNAL OF ENGINES, Part 2 (1990), pp. 2310-2330 (21 pages)

Cam lobes get to about 200C.

I'd expect the end of the camshaft, out of the oil and away from the sliding surfaces, to be quite a lot less,

Superglue only goes up to about 180C though (it failed almost immediately when I ran those tests comparing it with JB Weld High Temp epoxy...ooh...ages ago) so might be a bit marginal

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Thu 3 Aug 2023 20:26
I very much feel that your science is very useful to me. - paul 1963

Bit confused tbh, having had to take the head of again are you still intending to use the original gasket for the third time?

I do wonder at times ( yes I am that sad) if ultimately its really worth going to all the bother, bodging, and improvising, I know it's a bit personal but are you utterly skint or utterly mad?

Your quite clearly a educated guy and as such you must know that the chances of that engine ever running again are slim.

Edit: Another thought....is this whole saga make believe made up in order to amuse us?

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Fri 4 Aug 2023 00:25
I very much feel that your science is very useful to me. - edlithgow

I got a new gasket when the "saga" started, though somewhat against my better judgement, since I've re-used a head gasket in the past with no problem.

I have not renewed the head gasket each time I've taken the head off, though I suppose that would be ""received wisdom". I am not a huge fan of received wisdom, but If I have to do it again I might spray some stuff on it.

IF the engine runs again and the gasket fails in service, then I'll consider replacing it.

Re your financial and clinical diagnostic questions, you pose a false dichotomy. Its presumably quite possible to be both.

But are you a qualified psychiatrist?

If so I very much feel your science is very useful to...er...someone, but you must be quite busy.

I do wonder if ultimately its really worth you going to all the bother of reading and commenting on my posts.

Edited by edlithgow on 04/08/2023 at 02:50

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