F8B/F5A Flywheel differance

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Chris&Maz
Posts: 1
Joined: Sat Oct 15, 2016 12:28 am

I was wondering if any one could help.
Ive started a MB project and changed out the old F5A engine with manual 4 speed gearbox and fitted an F8B engine that had the 2 speed auto. removed the 2 speed and fitted the old manual gearbox and flywheel off the the old engine ( F5A ) to the new engine ( F8B )
i have fuel and spark, but not at the right time,i guess? will not start/run.  I have read that the flywheel and timing maker off a F8B is differant to the F5A flywheel?
Can any one conferm this and let me know what the differance is.
All help would be appreciated
Chris&Maz
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Brayden
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Joined: Sun Apr 11, 2004 3:09 am
Location: Canberra ACT
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Flywheels are the same in most cases, but the auto/manual have different timing markers (because the auto has a flex plate instead of a flywheel). Even if the timing is way out it should still start.
F8B EFI turbo - Three pots and a snail.
BLSTIC
Posts: 51
Joined: Tue Jul 05, 2011 10:04 am

Can't tell you that, but I *can* tell you how to make your own marks.

If (like me) you made special tools for it in machining class, you can screw in your top dead centre checking tool into #1 spark plug hole. If not, anything that fits in the hole that will positively stop the piston (or alternatively, move when the piston touches it and return to *exactly* the same spot when the piston moves back past the point) and not touch the valves is fine, say, a screwdriver with a a rubber band between the handle and some other thing on the engine.

You put #1 piston low in the bore (anywhere low is fine, doesn't have to be TDC). Then turn the engine over until it exactly makes contact with your tool. Mark this point on the harmonic balancer, against whatever else you want to mark it against (some particular bolt, or maybe an arrow you made on the timing case). Now wind the engine the other way until it again hits the tool. Mark this point on the harmonic balancer. Place a third TDC mark exactly half way between these points on the part of the pulley that didn't sweep past your indicator.

That last part might require some visualisation, perhaps this can help: Say you do the above procedure and you turn the crank exactly 90* between 'contacts' (remember, 360* in a circle). This would mean that each mark is at 45* before & after BOTTOM dead centre (alternatively, 135* before & after Top dead centre). So half way along the 270* that you didn't sweep is the true TOP dead centre.

After this, do math from this mark and the diameter of your crank pulley to lay down whatever timing marks you want.

If you do this and make a, say, 8* BTDC mark, you can then set the engine on this mark and rotate the distributor until the points open at exactly this mark on #1 compression stroke (do it with the ignition on and the cap removed from the distributor and you can *hear* the spark. Going from the max retard position in the 'advance' direction should ensure the points are opening, because there can be a small spark on points closed occasionally as well). This will be close enough to run properly, or at least start (assuming 8* is what you need to have. I've only seen one engine that didn't start with that timing, and it was a 13:1 compression engine with a marginal starter motor & battery)
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Brayden
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Joined: Sun Apr 11, 2004 3:09 am
Location: Canberra ACT
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Sorry I wasn't clear in my previous comment. When I say "different timing markers" I don't mean the marks on the flywheel/flex plate, I mean the little pointer (it probably has a name) that bolts on the block and lines up with the flywheel marks. The auto one is different to manual.
F8B EFI turbo - Three pots and a snail.
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