Timing chain change

[WIMPUS]

Hi all,

A friend of me is maybe in need of a new timing chain & co on his Spitfire 1500.
Now does someone know what he all needs and needs to do?
Or a guide of how to do it ? 🙂

Regards, Wim

[RobPearce]

If replacing the chain you should replace the two gears also, and while there you may as well fit a new tensioner. It's possible to do in situ, but the radiator will need to come out. The process is then something like:
- Line the engine up to a known position (TDC #1 firing) and lock it in place (I have a home-made "special tool" that fits in place of the starter motor)
- Unbolt the front pulley nut (which is quite tight!) then pull off the pulley.
- Undo all the timing cover bolts and remove the cover.
- Prize away the locking tabs and undo the two bolts attaching the large gear to the camshaft.
- Remove the large gear and chain.
- Pull the oil thrower and small gear off the crankshaft.
- Clean things up
- Fit the new small gear (it just slides on) and temporarily place the new large gear on to check alignment
- Adjust the number of shims behind the small gear, if needed, to get the chain run straight
- Fit the chain around both gears, adjusting position to get the best fit of the holes with the camshaft. Note the two sets of holes (for half-tooth adjustment) and the option to turn the large gear over (for another quarter-tooth)
- Once the ideal position is found, refit the large gear bolts with a new locking tab. Tighten to correct torque and tap over the corners of the tab
- Fit the new tensioner to the timing cover. Fit the oil thrower on the crank, then fit the timing cover with a new gasket. It may be necessary to employ a special tool (bit of bent metal) to pull back the tensioner to clear the chain.
- Tighten all the timing cover bolts to correct torque (which is quite low).
- Refit the pulley and nut, then tighten to torque (which is high!)
- Refit all the ancilliaries that had to come off to make room

[Velocita Rosso]

...but when refitting new, the cam and carankshaft must never have been moved when the old sprockets are removed, otherwise you have to start again with lining the marks up on the front plate and two sprockets with a 300mm steel rule.

[RobPearce]

True. I'm assuming the crank remains locked by the dummy starter all the way through the process, but the camshaft needs to be handled with care. Selecting a well-defined reference point helps - my suggestion of TDC probably isn't the best. If you start the job with, say, #1 inlet valve at full open (obviously rocker cover off to make this visible) then any movement of the camshaft can be spotted and corrected before reassembly.

[JohnD]

Measuring  TDC, or full lift with a dial gauge is always difficult, because the piston/cam follower comes to a halt at the top, and either side of the true point the finest gauge seems not to move.

A better measure for TDC is a piston stop.   This technique is described elsewhere so I won't repeat.

And for the correct setting of the camshaft, "Equal lift on overlap" also described elsewhere.
The latter works best with two dial gauges, but they are not expensive these days.

John

[Velocita Rosso]

However to make life easier/better...fit Duplex chain/ vernier timing gear as it can be adjusted far easier than moving sprockets around if you are a tooth out

[GT6 M]

I,ll add to above, to set it to  108 degs, { if a OE cam }
or 2 degs if any other mek,  ADVANCED,

this so that ina while when chain wears, it will end up at 110 as originally intended.
moer criticle with a single row chain  i would say.

when I took me olde,n oot, it were reading 115 degs, so it advanced 5 degs.
but then it had alottt of miles onit
M

[Velocita Rosso]

Quoted from GT6 M

but then it had alottt of miles onit
M

??

[Dannyb]

What about locking the engine with a bolt through the spark plug hole. Either modify an old spark plug by cutting off the ceramic  and inserting a bolt making sure the bit that touches the piston is nice a round to avoid damage. I think I read somewhere that the modern mini wheel bolt can be used has it is the right thread and length.

[drofgum]

Quoted from Dannyb

What about locking the engine with a bolt through the spark plug hole. Either modify an old spark plug by cutting off the ceramic  and inserting a bolt making sure the bit that touches the piston is nice a round to avoid damage. I think I read somewhere that the modern mini wheel bolt can be used has it is the right thread and length.

DannyB,
That is a good piston stop, but it won't lock the engine. The engine could always turn in the opposite direction. Locking the engine on a piston would also risk making a hole in the piston.
                                                                           Regards,
                                                                           Paul

[Marc F]

Very timely thread (if you will excuse the pun) as I need to refit all mine to a naked engine, and I am never sure I understand the process - I can line the piston up easily enough, but knowing where the camshaft needs to be is where I start to doubt myself. Happy to buy some dial gauges but is thre a step by step guide in idiot speak that I can follow.

In English though please if possible - I find Scottish a bit difficult to make sense of sometimes, just as I found the Haynes manual guide to be no use. My camshaft gear wheel has no markings on it, so I need to basically start from first principles to get the car set up straight.

Thanks

[Chris_68]

From JohnD that even I could follow.

Quoted from JohnD

Make up a piston stop, to help find TDC.
Even with a dial gauge, the piston rests at the top of the stroke through a significant number of degrees.  Deciding where TDC is can be a problem.   But half way up the stroke, the piston is moving maximally for every degree.

Stop the piston about halfway up the bore - the absolute point doesn't matter.
Then reverse it and stop at the same point from the other direction.
Note, using your degreeing wheel, where that is, and TDC is exactly halfway between.

You need a mechanical stop to be accurate.  A plate or bar across the bore, between head studs, with a bolt through it down into the bore, will do the job.   Can't send you a pic at this moment - I'm skiving at work - but if you ask I can do so from home.

John

Regarding the equal lift, with crancshaft at TDC set the degree wheel to zero, then rotate to 110 degrees ATDC and with no chain on the camshaft rotate cam until you have equal lift on 7 and 8, there you have 110 degrees. Put the big sprocket plus chain on it. Recheck everything so you have equal lift at110, go for a cup of tea and check again a couple of times... It might be a good idea to set a degree or two earlier, I have a duplex chain but will set it slightly less than 110.

/Chris

[JohnD]

Thank you Chris for digging that up ; I knew I had described using a stop before.   That refers to the short  block situation no cylinder head.  A spark plug stop will do as well.

Equal lift Ive alse decribed before.  Siuggest a search?  
I have made a video of ELoO but cannot find an editor as simple as Ms Movie Maker that will work on my W8 machine or with the footage from my new  HiDef camera.   Think I can fix the second.   Suggestions of a simple video editor please?

John

[Dannyb]

Quoted from drofgum

DannyB,
That is a good piston stop, but it won't lock the engine. The engine could always turn in the opposite direction. Locking the engine on a piston would also risk making a hole in the piston.
                                                                           Regards,
                                                                           Paul

I never intended it to be to lock the engine and would not use this nethod to undo the crank wheel. But it can used to mark where the crank and cam position are so the replacement can be put back exactly the same position. As long as you make sure the piston is up against the stop, or you could use more than one plug hole.

[Guppy916]

okay this might be too late but others can use it for reference,,,,,,,,,,,,,
Cam timing;
    Set no 1 piston to TDC (top of the bore) check this with a Dial guage. Note there is a 'dwell' period
    where you can turn the crank & see no movement on the dial guage. It may only be a fraction  of a turn
    but you need to find the mid point of the pistons TDC position.
    Next slip the chain over the crank & mount the timing disc TDC 0 degrees at the top. Bend a short length
    of wire & wind it around one of the studs that secure the front cover & secure with a nut & washer.
    You can then bend it into a pointer to the TDC position on the timing disc.
    The cam is timed in on the no 1 inlet so second lobe from the front, fit a cam follower making sure it
     drops easily & then another up side down on top so the dial guage can register on the flat cam follower bottom.
     Turn the cam until maximum lift is registered on the guage. Note there is a dwell period of maximum lift on
      the cam often up to 7 degrees so you need to find the mid point of the maximum lift.
      Turn the crank clockwise until the pointer is at 110 degrees ATDC (After Top Dead Centre)
      Now the cam chain wheel can be slipped on to the cain & offered to the cam shaft. This is the tricky part &
      usually requires several attempts to get it right. Once fitted turn the engine clockwise for several turns & then
      check the cam dial guage fo maximum lift & then check the crank degree is still @ 110 degrees. Re adjust if
      not spot on, can take some time to get the perfect setting