The Datsun 1200's A12 is an overhead valve engine
similar to my Toyota Corolla's 4K engine.

Does any Datsun owner here have problems with
their timing chain snapping ? This is because my
Toyota's chain has been rattling for a long time and
is actually long overdue for a replacement. I'm
thinking of having it replaced these few weeks.

I have been getting conflicting opinions from
different mechanics and friends. Some say that
that the short-type double chains in OHV engines
won't ever snap and never need replacing, even
if they make a lot of noise. They add that replacing
the chain in these kind of engines is a big hassle
and is normally only done when the engine is taken
apart at overhaul intervals.

Others say it can snap. Yet others tell me that even if
the chain does not snap, the tensioner may give way,
resulting in the chain flying loose.

I have never heard of an A series Datsun timing chain breaking, but if it is actually rattling, then something is very wrong and it will not get better. Save yourself some trouble in the future and pull the engine out and have a good look at why it is noisy. While it is out, slip the head off and have a look at the bores.
It might be worthwhile just laping the valves and giving it some rings and bearings to make the whole job worthwhile. It will be as good as new again.

yer im with u dats-hot, if its rattling bad u got to do somethin bout it.

Looks like a question about a Toyota motor snuck into a datsun forum covered with the mention of the A series.
We all know toyota mechanics, so its understandable
Years ago a friend's rollie had the same problem and we got a new chain and tensioner. We thought we were good and did it in the car. ( we realised later it would be way easier to just take the motor out)
Chain problem turned out to be a siezed tensioner that was easily fixed with some emery paper.
Both Toyota motors and the Datsun A series require the chain to stretch a friggin lot for the tensioner to become loose from stretch. The tensioners face also wear eventually.

Overall not a difficult job if we as young blokes could do it with just a workshop manual to guide us.

Thanks again, Phunkdoktaspot, Steven and
Dats-Hot, for the help.

Sorry to have to bother you people for help again,
but there is no similar Toyota KE70 website with
a good and very active forum like yours around,
apart from a couple in Yahoo which aren't very
good.

I'll go get the whole works - chain, tensioner,
sprockets and L-plate changed soon as I can. You
young guys are really good to do it yourselves - no
car owner in Malaysia knows how to do it
themselves. Has to be done by the mechanics, and
even they will take virtually the whole day to finish
it, replacing a timing chain is a really major job,
unlike a timing belt.

The cylinder head gasket and valve seals and guides
were changed a few months ago with a gasket set, and
the valves decarbonized. The tappets are making some
noise now, but the rattling is definitely the timing chain
- gets louder when the aircon compressor cuts in. It's
been rattling for years actually. It's even noiser if I use
a lighter oil such as SAE 30 or the 15W-40 which I am
using now. I'll have to switch back to 20W-50.

By the way, I think the earlier problem in my first post
about the engine idling roughly and stalling in hot
weather, might well have been vapor lock. I've wrapped
the fuel lines running to and from the fuel pump in
aluminium. If that still doesn't work, I might have to
change over to an electric pump.

Tham

I'm am replacing my timing chain in the next week or two - I've taken pictures of removing the timing chain cover at this web address.

Oh and the price in Australia of a new timing chain for an A14 engine was $10AUS. ($10.47 I think).

The worst bit about the whole process is changing the timing cover and water pump gaskets....as these were baked on with 30 years of operation on my engine and very very hard to remove.

http://mildman.datsunprojects.org/a15_prep_5.htm

Good luck

Hey man you say there is no forums active like this one.. go check out
Toymods
and
Rollaclub

these sites are very useful and i must admit update more regulary than this one..

im goin to upload a photo of my cam sprocket, its lets say....worn....

good day Tham I am from Malaysia too, Kuala Lumpur fellow but staying in PJ

ok so for timing chain I had this experince before so I can comments a bit here.

1. Timing chain will not break but what will happen when timing chain is loose is that it will hit our 4K engine timing chain cover = it does u need to change the timing chain cover

worst situation like my previous engine u can see a hole through it

2. Timing chain my advice is change the whole thing don't change bit by bit but change the whole timing chain plus the gears too.

4K engine there are two types of timing chain

a. single chian - meaning one timing chain

b. dual chain - meaning the timing chain has dual chain in it

hope this helps ur decision

Hey Cookie Malaysia, thanks for your help and info.

I work in Kuala Lumpur, but stay in Petaling Jaya too.
My handphone is 019-248 1387 if you would like to
reach me.

Wow, I better get the chain replaced soon as I can.
The rattling sound may well be due to the somewhat
loose chain hitting the cover as it rotates. I wonder
if it has eroded the inside of the cover already. I was
warned if the tensioner gives way, the chain might
fly off and punch a hole through the cover ! Sorry to
hear about your engine, was that what happened ?

I had bought a dual chain, plus tensioner, the two
sprockets, L-plate and gaskets for the timing cover
and oil sump some time ago. I note from Mildman's
website there's an oil seal in the timing cover too, so
will go get that as well.

Thanks for the help too, Tom210 and Mildman.

Good the hear you are giving it a try Tham...I assume your engine is similar to the A14 (with an oil seal in the front) - you will see it as you dismantle your engine.

Get some degreaser too and clean everything well while it is off the engine.