1986 Daihatsu Skywing - Ridges on Cambelt

Honest John Back Room » Technical matters
What is life like with your car? Let us know and win £500 in John Lewis vouchers | No thanks
View Threaded
Tue 2 May 2023 00:39
1986 Daihatsu Skywing - Ridges on Cambelt - edlithgow

Always managed to avoid these autodestructing interference rubber-band engines before, so havn't looked at many cambelts, and don't know if this is expected, and/or indicative of impending failure.

Looks like "print through" of the cam sprocket teeth onto the back of the belt

photos.google.com/album/AF1QipOlqdXkrhwsGpCYnW0jeb...T

tw.forumosa.com/t/ridges-on-timing-belt/229888

I was under the impression you usually can't tell if they are about to go bang.

IIRC its well below the mileage for a belt change, but I'll have to check my translation of the service records to confirm.

It isn't the result of stresses introduced by removing and suspending the cam sprocket, since the ridges were evident before doing that

Edited by edlithgow on 02/05/2023 at 05:17

Reply | Report as offensive | Link
Tue 2 May 2023 07:57
1986 Daihatsu Skywing - Ridges on Cambelt - Bolt

It isn't the result of stresses introduced by removing and suspending the cam sprocket, since the ridges were evident before doing that

imo, Looks normal to me, though how many years has it been on there, if getting close or over would recommend changing, as you said you cannot tell from looking how close they are to breaking point

apart from that is looks ok, but as deceiving as your bore marks, which I still think should be micrometred if thats the word?. to tell how deep the marks are

Reply | Report as offensive | Link
Tue 2 May 2023 09:16
1986 Daihatsu Skywing - Ridges on Cambelt - Andrew-T

Did they print manufacture dates on old cambelts ?

Reply | Report as offensive | Link
Wed 3 May 2023 01:23
1986 Daihatsu Skywing - Ridges on Cambelt - edlithgow

tw.forumosa.com/t/skywing-service-slip-sample-uh/6...1

Oo-er. Apparently it was changed in Feb, 2009. How time flies!

Can’t find a time limit advised in the manual, only a mileage limit, which it’ll be well under.

It does make sense that, being a rubber component, it would have one, as tyres do. I note Gates, a belt manufacturer, advise 72 months (six years) so its over twice that.

OTOH tyres have a date code on them so you know how old your replacements are.

AFAIK timing belts don’t, or if they do, I don’t know how to read it.

Manual also makes a big thing about not folding them through tight curves because it damages glass fibres. I’d be surprised if Taiwanese (or indeed most other) motor factors pay any attention to that.

I'll change it, but maybe only after the other issues are fixed and its passed inspection, which may never happen.

Only real solution is to avoid interference engines with rubber cambelts, but then I didn’t expect I’d have it for so long

Reply | Report as offensive | Link
Wed 3 May 2023 09:43
1986 Daihatsu Skywing - Ridges on Cambelt - Adampr

Given you've already got the head off, wouldn't it make sense to spend a few quid on a new belt?

Looking at the post in your link, it seems your HG has gone in the past. Whatever killed it may have done for your cylinder too? As you've got the head off, I presume you've checked it for cracks etc?

Reply | Report as offensive | Link
Thu 4 May 2023 00:13
1986 Daihatsu Skywing - Ridges on Cambelt - edlithgow

Dunno, given that the car may never run again (and/or may never pass inspection again) I’d say it was a pretty moot point.

OTOH IF I got it legal and then the rubber band went pop and wrecked the engine that would be annoying, so I got one. 350NT

Whether this DAYCO (Chinese outfit recntly mentioned on here as implicated in spate of Peugeot BIO engine failures) belt of uncertain age, (but stored in Taiwans heat and humidity for all of it, apparently bent double, and then installed by me), is a better bet than the Japanese (OEM?) belt installed by the Daihatsu dealer 12ish years ago, is something I can’t know at present, and hopefully never will.

I can't see a crack, but it would seem to be an explanation for the middle cylinder damage, which is a bit puzzling.

I can try and get a higher resolution picture than this (iPhone) one.

I suppose dye penetration testing would be one approach, but I dunno if I can get an appropriate dye test kit in Taiwan. Internyet-wise, shows on Indiamart, plus Shoppee Philippines and Malaysia,and Amazon, but Google doesn't seem to find anything locally

Maybe dyed penetrating oil, or just nail varnish diluted a bit further with acetone?

GF probably wouldn't miss a little bit.

This is strangely pointless...

www.youtube.com/watch?v=ao92ncBMhn8

Edited by edlithgow on 04/05/2023 at 02:45

Reply | Report as offensive | Link
Thu 4 May 2023 09:24
1986 Daihatsu Skywing - Ridges on Cambelt - bathtub tom

I don't think I'd be putting any chemicals on a belt I'd be re-using.

I'm interested in the top of your pistons, the depressions make it look like you've a single, large inlet valve and a smaller, inclined exhaust. Any chance of a pic of the head showing the valves?

Reply | Report as offensive | Link
Thu 4 May 2023 11:43
1986 Daihatsu Skywing - Ridges on Cambelt - edlithgow

I don't think I'd be putting any chemicals on a belt I'd be re-using.

I'm interested in the top of your pistons, the depressions make it look like you've a single, large inlet valve and a smaller, inclined exhaust. Any chance of a pic of the head showing the valves?

Don’t think I would either. I took the question about crack testing to be referring to the #2 cylinder wall damage, mostly because it said so.

I suppose mentioning this in a thread about the cambelt is potentially confusing, but I didn't start it, and since I've never heard of dye penetration crack testing of rubber, I didn't think of that interpretation.

I think there are links to cylinder head pictures in the cylinder head removal issues thread. Probably better to keep them there.

(Post 18th April - this is dragging on a bit - 3rd link down)

Edited by edlithgow on 05/05/2023 at 07:10

Reply | Report as offensive | Link

Looking for a garage you can trust? Honest John's Good Garage Guide has thousands of reader recommended garages, plus how-to guides and tips on servicing.

The Good Garage Guide