GT6 Mk3 only runs well with VERY advanced timing. Any ideas why?

[Straightsix]

Hi

Sorry to re ignite this thread, pun intended 😏

Following on from earlier posts I discovered the position of my dizzy was incorrect, the vacuum advance unit being too close to the block. Especially compared to photo provided by @Ian Foster 

So, after checking tappet adjustment, I went about correcting the dizzy position.

Firstly I connected strobe to no.1 ht lead to check timing as a reference before commencing work, all seemed well.

Secondly, I manually turned pulley to tdc position. No.1 cylinder on compression, rockers 1&2 closed.

Thirdly I removed dizzy checked drive gear orientation.

   I then re set drive gear slot as shown by @JohnD photo.

Re assembled everything, rotar arm now in six o’clock position.

 Started engine with strobe connected as before, painted timing marks no longer visible!  after a bit of head scratching I connected strobe to no. 6 ht lead and bingo timing marks re appear.

I’m a bit stumped why this has happened.

Any ideas? TIA

[Iain T]

First thought check plug leads are connected in the correct and positional order to the dizzy cap. 

Iain 

Edited November 29, 2023 by Iain T

[johny]

36 minutes ago, Straightsix said:

 Started engine with strobe connected as before, painted timing marks no longer visible!  after a bit of head scratching I connected strobe to no. 6 ht lead and bingo timing marks re appear.

I’m a bit stumped why this has happened.

Any ideas? TIA

That is strange because I can see my timing marks, as I should, on both leads 1 and 6. In fact its a good test to do to check the dizzy is able to repeat the correct timing in two places. Are you sure the mark isnt exactly under the pointer and so hidden?

[Straightsix]

I have since discovered the plug terminal in No1 ht lead is defective, maybe this is the cause?

Have ordered new, HT lead will report back when it’s delivered, expected early next week. 👍🏻

Cheers

 

[Iain T]

7 minutes ago, Straightsix said:

have since discovered the plug terminal in No1 ht lead is defective, maybe this is the cause?

It must have run rough! 

[Straightsix]

Wasn’t running that even, but as timing wasn’t set plus plug issue was new.

 

 

New HT lead fitted to no.1 and timing marks visible again 👍🏻

Idle a little uneven ,maybe the result of the cam that’s fitted as PO pointed out.

Revs cleanly, didn’t take it out for a road test tho, salt on the roads plus a snow covering here this morning!

Edited December 2, 2023 by Straightsix

[Cookie]

if anything the ignition needs to be retarded with modern fuels. I have a late GT^ MK3 engine and timing is supposed to be 10 deg BTDC according to the manual. However, although it tickover smoothly at that setting it pinks badly up hills. I've found that it needs to be set at about 6 deg BTDC to avoid pinking on modern fuels (and that's using 99 Ron super unleaded E5), at 7 deg or more it pinks badly, but at 6 deg it only pinks very occasionally.  Of course using e10 normal unleaded would need even more retardation to avoid pinking, but then GT6s were designed to run on 5 start leaded 100 Ron back in the day so that's not surprising.

 

I think as has been said that your pulley harmonic rubber damping has shifted and the scale on there is now way out. Quite a common issue on the pulleys on 6 cylinder cars when the pulleys get old and the rubber damping starts to break down.

 

[nicrguy1966]

6 hours ago, Cookie said:

if anything the ignition needs to be retarded with modern fuels. I have a late GT^ MK3 engine and timing is supposed to be 10 deg BTDC according to the manual. However, although it tickover smoothly at that setting it pinks badly up hills. I've found that it needs to be set at about 6 deg BTDC to avoid pinking on modern fuels (and that's using 99 Ron super unleaded E5), at 7 deg or more it pinks badly, but at 6 deg it only pinks very occasionally.  Of course using e10 normal unleaded would need even more retardation to avoid pinking, but then GT6s were designed to run on 5 start leaded 100 Ron back in the day so that's not surprising.

 

I think as has been said that your pulley harmonic rubber damping has shifted and the scale on there is now way out. Quite a common issue on the pulleys on 6 cylinder cars when the pulleys get old and the rubber damping starts to break down.

 

Thanks for the suggestion, and I wish life were that simple, but I don't think the timing mark is incorrect for several reasons.

1) I felt the position of piston #1 and it matched the timing mark

2) I removed the crank pulley and inspected it, there's no sign of any issue with the rubber and it wasn't possible to move the mark.

3) The timing of the cam shaft was wrong in the opposite direction to the problem with the ignition (cam was too much ATDC, ignition is too much BTDC)

4) I've set the cam timing based on the TDC mark, and if it was as wrong as the ignition timing, I doubt the car would even start, but it runs well.

[Iain T]

Have you fitted the new lead on No1 cylinder? Out of curiosity I would have fitted No 6 on No1 to see if the timing was correct. 

Iain 

[Pete Lewis]

most/many  strobes have a arrow on the HT pickup  (points to the plug)    get it back to front can give some crazy results 

just a thought 

Pete

[Firefly]

   Cookie,

               Interesting post, had the same issue with my GT6 engine in my MGB GT. Had knocked the timing back to 7 Deg BTDC, and it would pink on e10 and e5. So decided to set the timing the old way, at tick over, and advance to max RPM, then back off a little. Took it for a spin and couldn`t make it pink. Checked the timing with a strobe and its at 17 Deg BTDC.🤔 And no there is no rubber slippage on the pulley, timing marks were checked 3000 miles ago during complete rebuild, and checked again when I advanced the timing just recently. Sure there`s another 10 BHP on tap as well, and it runs happily on e10.  I know this defies all logic, but think it could be down to the way modern fuel burn???     Mac.

                                                        

[johny]

I hope you didnt leave it at 17º BTDC? Theres no advantage in going beyond the manufacturers figure and indeed even a risk of damage. The energy in the fuel is the energy in the fuel and if burnt without pinking you cant get anymore out of it, unfortunately😒

[Firefly]

      Yes it`s  staying at 17 Deg BTDC, I`ve been around engine over 50 years and know when an engine is happy or not, including working at Triumph all thro` the 1970`s. Indeed an engine can be damaged, particularly by pinking which is suggesting the fuel isn`t being burnt  properly. So I`ll let you know when the heads blown off. 😀    

[johny]

ha ha seriously though keep an eye on the compression readings (burnt valves) and its occurred to me that a reason for not getting pinking at high levels of advance might be low compressions.... 

[nicrguy1966]

44 minutes ago, Firefly said:

      Yes it`s  staying at 17 Deg BTDC, I`ve been around engine over 50 years and know when an engine is happy or not, including working at Triumph all thro` the 1970`s. Indeed an engine can be damaged, particularly by pinking which is suggesting the fuel isn`t being burnt  properly. So I`ll let you know when the heads blown off. 😀    

Even after all my messing about, I'm pretty sure my engine is back at around 20 degrees BTDC. I've adjusted the timing 'by ear' a couple of times since changing the cam timing, each time slightly advancing the timing. With each adjustment, low rev power has improved, without power loss at high revs or pinking.

I'll dig the strobe out again once the weather warms up.

My current thoughts are around a new distributor in the new year.

[Firefly]

 

    Jonny I have great respect for your input to the forum. This is an experiment at the mo, and will be watching things closely. I havn`t done a compression, because it had a rebore, new pistons and an unleaded head during the rebuild. I think it is more likely to cause valve damage with preignition than as it is at the mo, time will tell.   Mac      

[johny]

Thanks yes just bouncing ideas around as these issues of over advanced timing are very mystifying...

[Firefly]

 

           Mystifiying  indeed, just for info, during the rebuild I manages to get my hands on a NOS distributor, and have checked its performance, spot on as you would expect. I`m no chemist or fuel expert, but I suspect the petrol, because its very different to the old unleaded they were design to run on. Perhaps its no coincidence that nicrguy  has found almost the same amount of advancement has given him his best results, defies everything we though we  knew about ICE`s. 

[johny]

well Im nowhere near an expert on this but I suppose its possible that although the fuel companies have to reduce the octane level for fuels with ethanol to keep it correct its not to say other characteristics such as burn speed arent different.  If this is the case and burn speed is slower then there might be a benefit to igniting the mixture earlier than standard to ensure maximum cylinder pressure is still achieved at the right piston position...

[Firefly]

 

           My thoughts exactly Jonny. 

[Iain T]

In the search for the perfect ignition timing on my uprated engine with 10.5:1 CR I tried adjusting using the manifold vacuum method. Someone mentioned as I have K&N filters they do allow more air in so can muck up the tickover vacuum but in fer a penny. I was surprised when the highest stable reading was around 20 degrees advance! Nice tickover and felt very lively and responsive on the road and no pinking using Momentum 99 octane. I bottled out and put the timing back to 10 degrees. Some time later I had my distributor refurbed and advance curve calibrated by the Distributor Doctor for my engine spec. In a conversation he said you'll probably need more advance than standard to get the best performance. This was not what Google said for a higher CR! I rang back and questioned the higher advance and he said just keep on advancing until it pinks then back off or in other words the timing marks are there for info only! 

Mac aka Firefly let us know how it goes as I'm tempted to go down your route and rely on the engine feel and Distributor Doctor and not on Google search!

Iain 

[Firefly]

 

               👍 Will do, but I don`t clock up many miles, especially this time of year. I`m convinced that Johny`s last reply hit the nail on the head, and D.D. seems to agree, so I`m happy to leave it as it is.     Mac

 

[Iain T]

1 hour ago, johny said:

well Im nowhere near an expert on this but I suppose its possible that although the fuel companies have to reduce the octane level for fuels with ethanol to keep it correct its not to say other characteristics such as burn speed arent different.  If this is the case and burn speed is slower then there might be a benefit to igniting the mixture earlier than standard to ensure maximum cylinder pressure is still achieved at the right piston position...

A quick search (I know it's dangerous) and found the higher the octane the slower the burn or E5 should burn quicker than old 100 octane therefore require less advance? 

Iain 

[Firefly]

        Well I live in my world, and listen and feel to what the engine is telling me, and if its happy at 17 Deg BTDC who needs Google??🙃😀

 

[johny]

10 minutes ago, Iain T said:

A quick search (I know it's dangerous) and found the higher the octane the slower the burn or E5 should burn quicker than old 100 octane therefore require less advance? 

Iain 

Unfortunately it seems rather complicated. When saying burn speed I think it refers to a higher octane fuels resistance to preignition which means you can compress the mixture and it wont self ignite thus its burn can be slowed by waiting until the spark comes....