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 Post subject: Valve springs
PostPosted: 08 Sep 2016 16:05 
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Joined: 20 Dec 2006 19:22
Posts: 56
Location: Melbourne, Australia
Does anyone have the measurments of the 4G92 mivec CA4A mivec valve springs?

Magn1t do you have the measurments of your 6G72 springs? Or have one spare to measure? I believe they are the same part number.
If I can get a measurement of:
Inner diameter
Outer diameter
Free length
Installed length (if possible but not critical as the workshop manual states 44.5mm but I like to confirm)
I'm going to change mine and with these measurments I can hopefully buy some springs to the rate I require without pulling my car apart. (knowing i may have to return them if the measurement is wrong or my car is different)

Thank you in advance.
Jason

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4G93 Mivec Turbo.
GT3076, Motec, Forged etc.
ADR 37/01 Legal.


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 Post subject: Re: Valve springs
PostPosted: 10 Sep 2016 20:25 
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Joined: 04 Jul 2005 13:25
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Location: Lower Hutt
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I'll try to get some measurements on Monday.
Yes, I've got a box of valve springs sitting loose.

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6G72 mivec Twin TDO5 20Gs up and running.
6G72 mivec bored and stroked to 3.4 litres...Frankenmitsi build
6G74 mivec bored and stroked to 3.9 litres....Frankenmitsi build.
6G75 under construction....4.2 litres bored and stroked.Another Frankenmitsi.


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 Post subject: Re: Valve springs
PostPosted: 10 Sep 2016 21:32 
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Joined: 20 Dec 2006 19:22
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Location: Melbourne, Australia
Thanks man.
Although the more research I do the less things are adding up. Mitsubishi CAPS and the 4G9x manual even have contridicting info. So I think I will have to pull it out as I think the ID is 19mm and OD is 27.9mm same as an EVO but an EVO has 40mm seat height and apparently the mivec has 44.5mm but doesn't tally up when comparing free lengths and seat pressures from the workshop manual.

Sometimes it's incredibly frustrating working on a car no one has any idea about and no real aftermarket parts or support.

Jason.

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4G93 Mivec Turbo.
GT3076, Motec, Forged etc.
ADR 37/01 Legal.


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 Post subject: Re: Valve springs
PostPosted: 14 Sep 2016 12:48 
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Joined: 04 Jul 2005 13:25
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Location: Lower Hutt
Country: NZ
6G72 mivec valve springs.

Free length 51 mm
OD 29 mm
ID 19 mm

Roughly.

Installed height is a bit more tricky, as is installed load, but can be done.


The non mivec springs are shorter as are the non mivec valves.
A longer valve stem allows a longer spring which allows more lift without coil bind.

Jayz-1 wrote:
Sometimes it's incredibly frustrating working on a car no one has any idea about and no real aftermarket parts or support.

Jason.


Not really.
Once you've been around cars as long as I've been then you'll know that most aftermarket parts are rubbish and available specs are wrong.

You've got to figure it out by measuring yourself.

_________________
6G72 mivec Twin TDO5 20Gs up and running.
6G72 mivec bored and stroked to 3.4 litres...Frankenmitsi build
6G74 mivec bored and stroked to 3.9 litres....Frankenmitsi build.
6G75 under construction....4.2 litres bored and stroked.Another Frankenmitsi.


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 Post subject: Re: Valve springs
PostPosted: 14 Sep 2016 13:45 
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Joined: 20 Dec 2006 19:22
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Location: Melbourne, Australia
I've been working on this same engine for 16 years. (11 years for the mivec head)

Thanks for measuring that. Looks like those measurements are matching the service manual for free length. Installed is what I need to work out now.

The frustration comes from the fact according to Mitsubishi CAPS it runs the same spring part number as the 4G93 DOHC but in the service manual it lists different free hight 51mm mivec and 45mm non mivec. But the installed heights are 44.5mm for both. But this can't be the case as the non mivec would have no preload on the spring.

Anyway I'll have to measure what my installed height is. I'm thinking it will be 44.5mm or 37.5mm based on some information and conclusions I've come to.

Unfortunately if I'm accurate and I have been getting valve float all these years I don't know if new stock springs will be enough. Stock mivec according to the manual is 57lbs at installed height. EVOs are 66lbs at installed height. Some people with EVOs get away with the stock ones and make decent power. Other people get float. Change springs to stiffer aftermarket ones and pick up 100 hp at the wheels with no other changes.

My plan is to get mine out and measure everything including the pressure at the seat and max lift. And if mine are 50 lbs (I'd assume losing 10% over 20 years is acceptable)
Then I'll have to make the decision on if new OEM ones will be enough or if I need aftermarket (I'm sure OEM didn't test for the 30 odd psi I'm adding to the mix)

Thank you again for your help.

Jason.

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4G93 Mivec Turbo.
GT3076, Motec, Forged etc.
ADR 37/01 Legal.


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 Post subject: Re: Valve springs
PostPosted: 14 Sep 2016 17:53 
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Joined: 04 Jul 2005 13:25
Posts: 1209
Location: Lower Hutt
Country: NZ
Springs DO lose tension over time.
The hotrodder's trick is to put washers under them. Just check for coil bind at full lift.

I've got a pair of heads somewhere with valves still fitted, will see if I can measure the installed height.
I might be able to measure load at installed height too.
I need to know for myself anyway so not a big deal.

_________________
6G72 mivec Twin TDO5 20Gs up and running.
6G72 mivec bored and stroked to 3.4 litres...Frankenmitsi build
6G74 mivec bored and stroked to 3.9 litres....Frankenmitsi build.
6G75 under construction....4.2 litres bored and stroked.Another Frankenmitsi.


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 Post subject: Re: Valve springs
PostPosted: 14 Sep 2016 18:09 
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Joined: 20 Dec 2006 19:22
Posts: 56
Location: Melbourne, Australia
I think I'll pull mine out this weekend and try to measure them. Or I'll just go to a spring place and get them to measure a few.
I'm not sure if a washer will be enough. As by my calculations a 1mm washer will add about 8lbs. But dependant what mine are I don't think it will get me to the 75lbs - 85lbs seat pressure I think I need.
If i bought stock springs i don't know how comfortable I feel shiming them the 3mm to get the seat pressure I want (if coil bind isn't an isue that is)

Yeah if you can measure yours will be good. More data is always a good thing.

_________________
4G93 Mivec Turbo.
GT3076, Motec, Forged etc.
ADR 37/01 Legal.


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 Post subject: Re: Valve springs
PostPosted: 15 Sep 2016 14:18 
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Joined: 04 Jul 2005 13:25
Posts: 1209
Location: Lower Hutt
Country: NZ
I've done a rough measurement of the installed height of a 6G72 mivec spring.
44 mm is as close as I can get.


I've also had a look on the 4G9x service manual that I've downloaded from here.
The free height is all you really need to measure.
51.5 mm is the spec, 50.5 mm is the limit.
Mine are right in the middle, so maybe the springs are identical?
When a spring looses it's strength, it sags so that the free length is shorter.
So long as the spring is more than 50.5 mm free length then the loading at the installed height should be correct, or at least within the limit. If the spring tester doesn't agree, then it needs rethinking?
If the seats or valves have worn a lot, then the installed height increases and the seat load goes down.


I'm still not sure what the symptoms of valve float actually ARE.
You certainly can't go wrong by measuring everything to the max.
I think that often it's an ignition problem where it's misfiring and loosing power at higher revs.
With a turbo , the same thing is easier to diagnose because you can turn the boost down until the problem goes away.
Using the same idea, you could adjust the throttle so it only half opens but still revs right out.

Ignition problems are load and related.
Valvetrain problems are RPM related.

_________________
6G72 mivec Twin TDO5 20Gs up and running.
6G72 mivec bored and stroked to 3.4 litres...Frankenmitsi build
6G74 mivec bored and stroked to 3.9 litres....Frankenmitsi build.
6G75 under construction....4.2 litres bored and stroked.Another Frankenmitsi.


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 Post subject: Re: Valve springs
PostPosted: 15 Sep 2016 15:24 
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Joined: 20 Dec 2006 19:22
Posts: 56
Location: Melbourne, Australia
According to Mitsubishi CAPS the part number is the same between your head and mine. Aswell as the 6A12.
So based on your measurments it looks like the factory service manual is accurate for the mivec.
I've had ignition issues in the past and had fixed them with what I believe to be the correct dwell settings that someone got out of the stock ECU, aswell as lower plug gap. (I tried different leads, coils and igniter with other spares I had with no difference)
When it would miss it was quite noticeable to the ear. But that's not the case as it still revs fine on the butt dyno but on a real dyno just goes flat at 6000 rpm. (If i don't change to the big cams over it falls over at like 4000rpm)
Adding 6psi more boost made 11kw difference which isn't right for a 600 hp turbo

I have always toyed with the idea of running 2 igniters in parallel and either have the second one turn on with the mivec output from the motec Or just half the dwell in the motec and run them both all the time (so I dont overheat the coils.) But as the noticeable miss went away I didn't think this was necessary.

Valve float has been discussed by a few mates of mine. Some say definitely that it's the problem. Others don't think so. I've tested and have changed quite a bit of the bolt on parts through out the years. The only thing I haven't done is anything to the head which makes me also think valve springs is a possibility. Unfortunately you can't really perform a test other then measure and replace if no good.

Just a process of elimination I guess. Taking the valve springs out isn't too bad as I can also check piston to valve clearances which I never did when I built the motor when I was 22. As well as if I do install some cams with more lift I may need springs anyway to suit the new cam ramp rate.
Do you have a magic ball that can give me the answer to my problem? :)

Thanks again for taking the tI'm to measure stuff for me.

Jason

_________________
4G93 Mivec Turbo.
GT3076, Motec, Forged etc.
ADR 37/01 Legal.


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