Jump to content


Photo

Crank Installed Backwards?


  • Please log in to reply
15 replies to this topic

#1 dggt6

dggt6

    Just passed my test!

  • Members
  • 171 posts

Posted 17 June 2017 - 07:17 AM

Is there any part of the 4 stroke engine cycle that sees the piston going down when the exhaust valve is open?

 

I have had my crank reground and I have refitted it back into the engine without moving the camshaft (or so I believe).

 

I believe I have refitted the sprockets the same way, aligning up the same marks. (I took photos)

 

On trying to start the car it was "backfiring" through the inlet and blowing off the plenum. (It looked nice at night time with little blue and yellow flames!!)

 

The car is on MS2 with EDIS6 and after replacing the coil pack, I realised the EDIS module was crook. With a good 2nd hand EDIS I an still getting back firing. :wallbash:

I have checked VR alignment with the trigger wheel and the timing light is firing at 10BTDC on the pulley.

 

In desperation I have whipped the rocker cover off to check the valve positions and the No.1 spark plug out to check the piston travel. :craig:

 

I thought the exhaust would only open when the piston was going up (give or take a bit of overlap)

 

WTF have I done????? :o , but more importantly, how do I fix it!!!!

 

Many thanks,

Doug

 

 

 

 



#2 Nick Jones

Nick Jones

    Wise beyond his years.

  • Administrators
  • 6,633 posts

Posted 17 June 2017 - 08:22 AM

To answer your original question, the exhaust valve opens at the bottom (or towards the bottom if a wild cam) of the firing stroke and remains open for the following up stroke.

 

Crank rotates clockwise as seen from the crank pulley end.  Does the engine sound normal when cranking - can you hear compression strokes?  Have you compression tested it?  If it seems to be pumping air normally then my prime suspect would be plug lead order - something that always gives me trouble with the Ford coil packs.  The numbers that Ford put on them do NOT work for a Triumph S6 as the firing order is different!

 

The pack has 3 coils in it. Pair should be 1&6, 2 & 5, 3 & 4.  Then there is the order that the coils fire in.......

 

Nick



#3 JohnD

JohnD

    Loves monkeying with his car

  • Supporter!
  • 2,761 posts

Posted 17 June 2017 - 08:29 AM

This is a GT6?

 

EDIS is a 'wasted spark' system that fires around TDC on both ignition and  'overlap', between the last and next four stroke cycles.    Normally, all the fuel has burnt when it fires the second time, so nothing happens, but clearly that is not true on yours, the fuel fires and as both the inlet and exhaust valves are open, you get backfire down both ducts.  Wasted spark is a common eletronic system, and this is not a fault.

 

But you are running Megasquirt (yes?).   The spark is not igniting fuel where it should, after the compression stroke, but after the exhaust stroke, on overlap .   So I presume that injection is occurring at the wrong time, synchronised with the wrong part of the cycle.

 

Suggest you pursue that fault, as ignition timing probably correct(ish).

I fon't know enough about Megasquirt to advise you.

 

JOhn



#4 dggt6

dggt6

    Just passed my test!

  • Members
  • 171 posts

Posted 17 June 2017 - 09:20 AM

Many thanks Nick and John for your continued support of forum members.

Yes GT6 with 2500 motor that was running quite well on MS2 with EDIS as I drove it into the garage to upgrade to an O/drive box. A new clutch and thrust washers and reground crank later, the engine goes "pop" not "broooom"!

 

"the exhaust valve opens at the bottom"   that's what I thought.

As I am watching No.1 piston come up, the exhaust valve starts opening and remains open as the piston passes TDC and travels back down. The exhaust valve closes when the piston is a long way down the cylinder. (the exhaust valve is the 1st valve, closest to the radiator?)

 

The engine does sound "funny" when cranking but I have a hi torque starter that I am not quite used to yet..  I did notice that the engine was spinning nice and quick without the spark plugs in and I was patting myself on the back that the crank reassembly must have been good.

However I also noticed that when I was cranking the engine WITH the plugs in (no fuel ) it seemed to spin almost as fast when there was no compression(no plugs).

 

Yes the Ford coil packs have given me a HUGE amount of grief also. My original pack had the 4 pin plug pin-out different to what was shown everywhere else on the internet. The new VDO pack seemed to be a third variation on position of the 4 pin plug as well as the pin out order.

So far I have not found the pack firing order of the VDO but the other 2 packs fired in the ACB order. I have assumed the VDO follows this sequence and have used the timing light to check that the packs are firing in that order at 60 degrees around the crank pulley.

 

Why do I get this feeling that the engine will have to come out again!!!!!!!

 

Cheers,

Doug



#5 oldtuckunder

oldtuckunder

    Fast Driver!

  • Members
  • 477 posts

Posted 17 June 2017 - 10:53 AM

I know little about MS2 or wasted spark, however from your description it sounds like if you didn't  have wasted spark the engine wouldn't be running, from your valve description it sounds like the cam is 180deg out which is easily done when refitting,  and also easily done if you time the crank using #1 valve instead of #1 inlet (don't ask how I know!)  :whistling:

 

Alan



#6 dggt6

dggt6

    Just passed my test!

  • Members
  • 171 posts

Posted 17 June 2017 - 11:18 AM

Thanks Alan,

I don't know I dun it but I think I somehow I installed the crank out of wack. I thought I had all the timing marks lined up????

I didn't remove the cam from the engine (or move/rotate it I thought).

Is it just a matter of taking the timing sprockets off, rotating the crank 1 (or is it 1/2?) revolution then reassemble?

 

Cheers,

Doug



#7 Nick Jones

Nick Jones

    Wise beyond his years.

  • Administrators
  • 6,633 posts

Posted 17 June 2017 - 12:32 PM

Does sound like cam timing could be wrong.....

 

Don't need to pull the engine again, just the front pulley and timing cover.  I'm not going to predict just how much of a revolution of the crank you'll need but it won't be a full revolution as that'll put you back where you are now......

 

Be glad this is a non-interference engine so no harm done except lost time and singed pride!

 

Nick



#8 JohnD

JohnD

    Loves monkeying with his car

  • Supporter!
  • 2,761 posts

Posted 17 June 2017 - 01:50 PM

A way of telling if the cam timing is right - exactly right if you measure it - without any dismantling except to remove the rocker cover is to use "Equal lift on overlap".

 

As above, both valves are closed in the 'Compression' stroke, but the exhaust valve is open in 'Exhaust' and closes just after TDC, while the inlet opens just before that same TDC.

Both valves 'overlap' around that TDC, and the Triumph camshafts, as most others do, open equally actually at TDC.

 

So, set the crank to TDC, with No.1 cylinder's valves both closed.

Remember that No.1 and No.6 move in synchrony, but fire on alternate cycles, so if No.1 is on the firing stroke, No.6 is at the end of one 4-stroke cycle and the beginning of the next.

Look at No.6.   Both valves should be slightly open.   By rotating the crank to and fro, you can see them move.  If you can, measure by how much they are lifted at TDC.  A pair of dial guages is the pro way, but you could measure them with a vernier depth gauge. They should be the same height at TDC, if your cam timing is correct.

 

This tecnique is vey accurate, good for checking, and for setting cam timing, indeed it's recommended in the OE Workshop Manual if your cam sprockets are unmarked.

 

John



#9 Nick Jones

Nick Jones

    Wise beyond his years.

  • Administrators
  • 6,633 posts

Posted 17 June 2017 - 02:36 PM

Good call John.

 

Described here:

 

cam timing page.jpg

 

Nick



#10 dggt6

dggt6

    Just passed my test!

  • Members
  • 171 posts

Posted 18 June 2017 - 06:40 AM

OK. I am gunna start from scratch and bugger the timing marks/dots.

With the timing chain off, I have valves 11 and 12 rocking and I have measured the lift and they are as equal as I can get them with a vernier caliper.

I have rotated the crank and got as close as I can with No.1 piston at the top.

Now just "slip" the chain back on and job done! Right?

 

Cheers,

Doug



#11 JohnD

JohnD

    Loves monkeying with his car

  • Supporter!
  • 2,761 posts

Posted 18 June 2017 - 09:21 AM

Right!

 

Remember that Triumph were clever with the cam sprocket.

Look this up (it's in the OE WSM, or here) Each tooth is about 2 degrees, so thats the closest you can get, BUT there are four bolt holes for two bolts.   The other pair is offset.

Turn the sprocket 90 degrees for a half tooth adjustment.

Turn it back to front for a quarter tooth

Or back to front and 90 for three quarters.

 

Check the No.6 valve heights after.

 

John

 

PS the other problem with cam timing is finding true TDC.

Even with a dial guage, the piston stops at the top, through several degrees, so where is it?

Use a piston stop, a bracket that physically halts the piston halfway up the bore.

Use a circular protractor to measure the point at which that happens;  turn the crank around the other way until it stops again.

Then TDC is EXACTLY half way between this points, in the arc that the crank could not complete.

 

You have your cylinder head on, so if you can arrange someting that pokes through the spark plug hole.

I took the porcelain out of an old spark plug, and ran a tap down it for a length of threaded rod.   See pic.

 

 

Attached Images

  • Spark plug piston stop (1).JPG

Edited by JohnD, 18 June 2017 - 09:29 AM.


#12 rogerguzzi

rogerguzzi

    Just passed my test!

  • Members
  • 173 posts

Posted 18 June 2017 - 10:06 PM

Right!

 

Remember that Triumph were clever with the cam sprocket.

Look this up (it's in the OE WSM, or here) Each tooth is about 2 degrees, so thats the closest you can get, BUT there are four bolt holes for two bolts.   The other pair is offset.

Turn the sprocket 90 degrees for a half tooth adjustment.

Turn it back to front for a quarter tooth

Or back to front and 90 for three quarters.

 

isn't that only possible with a simplex chain and not duplex(that's if you have up graded to duplex!)

 

but I may wrong(often am!)

 

Roger

 



#13 Nick Jones

Nick Jones

    Wise beyond his years.

  • Administrators
  • 6,633 posts

Posted 19 June 2017 - 12:42 PM

Think you are correct Roger.

 

Nick



#14 JohnD

JohnD

    Loves monkeying with his car

  • Supporter!
  • 2,761 posts

Posted 19 June 2017 - 02:16 PM

My duplex is a vernier sprocket, but I don't see how a plain duplex cannot be turned through 90 degrees, or reversed, unless it only has two bolt holes.

But it does! - a TR6 duplex cam sprocket has the same four holes, one pair offset, as does the singlex, as turning to page 12.41.05 of my TR6 WSM proves.

 

However!    The TR6 WSM makes no mention of turing or reversing the duplex sprocket, but the Haynes manual for the 2500, does,  so if you can explain why it can't be turned, I'll be grateful.

 

 

 

As an aside, the WSM describes purely "Lift on Overlap" to set the can timing!    The 'magic number' method is ignored.

 

AND, it has another method of finding TDC!

Many may have noted a mark on the rear engine plate, at the top of the flywheel.    I know I have, but I don't know which enghines had it.

The method is to find the highest point reached by the piston and to scribe the flywheel adjacent to the mark.

Then turn the crank the other way, find the highest point and make another mark.

"true TDC bisects the gap between the the two scribe marks".

 

And the WSM suggests you mark that point with a cold chisel!

 

This is the same as the piston stop method, except it still relies on a subjective judgement of when the piston stops rising.

 

John


Edited by JohnD, 19 June 2017 - 02:17 PM.


#15 dggt6

dggt6

    Just passed my test!

  • Members
  • 171 posts

Posted 24 June 2017 - 12:27 PM

SOLVED!!! :banana:

It was "the old EYE DEE 10 T " problem. More commonly known as the IDIOT symptom. :stupid:

The cam and crank sprockets were aligned, but 180 degrees out (backwards?). I was pedantic about re-aligning the sprockets but totally forgot to check which part of the 4 stroke cycle the cam was on. :wallbash:

 

Thank you everyone for your assistance. :thanks:

Now back to fitting the O/D gearbox installation project that started all this 7 months ago!!!!!! :craig:



#16 oldtuckunder

oldtuckunder

    Fast Driver!

  • Members
  • 477 posts

Posted 24 June 2017 - 01:08 PM

We have all been there and bought the T shirt (at least once).

 

Alan






0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users