Engine only runs under too much advance

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ajsimmo
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Re: Engine only runs under too much advance

Post by ajsimmo »

Mooney wrote:Yeah it happened when i fitted an exchanged engine. Got it from Elite which i know doesn't have the best reputation on here but i was on a budget. It does sound like it runs fine but obviously i'd like a more concrete way of measuring this. If the camshaft was incorrectly fitted would it still run fine if i adjust my dizzy like i have?
Possibly, for example if the cam was inserted a tooth or two out it would still run but probably have low vacuum at idle, and increasing spark advance might compensate for the symptoms.
I'm not saying it must be that, just throwing it in the ring to be investigated as one possibility.

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Re: Engine only runs under too much advance

Post by Mooney »

Hopefully not, would there be any way i could check for this without taking the engine apart?
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Re: Engine only runs under too much advance

Post by ajsimmo »

There's an approximate way of measuring the lift at the valve, and calculating back from there. The cam timing is available on Brickwerks site here:
https://www.brickwerks.co.uk/dg-engine-data/

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Re: Engine only runs under too much advance

Post by sarran1955 »

Hello,

1 dot out on the cam...

Sounds feasible....

Crazy timing and poor performance..

We will know when the patient is opened up... :wink:

Cordialement,

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Re: Engine only runs under too much advance

Post by Mooney »

So if i'm reading this right, the inlet valve on Cylinder #1 should start opening where my 5 degree BTDC mark is on the top of the engine? Is that how i'd check it?
ajsimmo wrote: 03 Sep 2020, 18:09 There's an approximate way of measuring the lift at the valve, and calculating back from there. The cam timing is available on Brickwerks site here:
https://www.brickwerks.co.uk/dg-engine-data/

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Re: Engine only runs under too much advance

Post by 937carrera »

Here's what my approach would be - as it is quite difficult to assess when the valve is actually opening do the measurement from maximum valve lift:

Inlet opens 5 BTDC
Inlet closes 34 ABDC

Inlet duration = 219 degrees

Point at which max lift is achieved 109.5 degrees after 5 BTDC so 104.5 degrees ATDC

Do the test on inlet 1 and measure how many degrees round from TDC the crank pulley is at peak valve lift. No disassembly required

I'll let those who do this stuff on a daily basis correct any errors :)

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Re: Engine only runs under too much advance

Post by ajsimmo »

Well I chucked that into the ring hoping someone else would pick up the maths job - it worked
If you pop a dti on no.1 (or 3 if easier) inlet valve spring retainer top, and turn engine (by hand ) until it reads 1mm lift from base reading, the pulley should be sitting very near the 5° BTDC timing mark (early cam) or 1° (nearly TDC) for the later cam.
If it's a tooth out (there are 25 teeth on the crank gear) that equates to over 14° difference, so you don't need to be super accurate, it'll be obvious!

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Re: Engine only runs under too much advance

Post by Mooney »

Thanks both for the detailed responses, will try and have a go at it this weekend! What's a DTI? Tried googling it with valve lift measurer and not getting anything back
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Re: Engine only runs under too much advance

Post by paperhouselad »

Hi, dti stands for ... dial test indicater. 

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Re: Engine only runs under too much advance

Post by Mooney »

Cheers haha
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Re: Engine only runs under too much advance

Post by 937carrera »

also known as a dial gauge

Dti method is superior, but if you don't have one available (my assumption) then the alternate can work.
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Re: Engine only runs under too much advance

Post by tobydog »

Check the tdc mark on the pulley with the timing mark?
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Re: Engine only runs under too much advance

Post by davidoft1 »

i would suspect your distributor is failing, i would also check with another timing light, its not unusual or timing lights to be out of spec

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Re: Engine only runs under too much advance

Post by tobydog »

937carrera wrote: 04 Sep 2020, 19:37 also known as a dial gauge

Or a clock 8)
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Re: Engine only runs under too much advance

Post by tobydog »

davidoft1 wrote: 04 Sep 2020, 19:41 i would suspect your distributor is failing, i would also check with another timing light, its not unusual or timing lights to be out of spec

Idle stabilizer......
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