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Author Subject: Max lift at TDC?
welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

Posts: 25,817

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Post #1
Anyone know how much clearance there is in the standard engine?

I know there are people running PT81's without larger cutouts and they are meant to be set to 1.65mm IN and 1.4mm EXH lift at TDC.

Also, if nobody knows the above what's the thickness of a standard gasket? I think its 1.20mm same as the J4R but it is a different part number...

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Posted 6th May 2009 at 21:44
adam b

Seasoned Pro

Location: The Nam

Registered: 24 Jan 2006

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Post #2
Didn't Sandy post this on the psooc a few months ago? There is only just enough room for the PT81s, really only just according to Sandy.

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Posted 7th May 2009 at 00:47
welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

Posts: 25,817

Status: Offline

Post #3
ahhh thanks for reminding me, I'll have a look Smile

edit; found it ta! Big grin

quote:
Valve to piston clearance in the GTI6 is very tight and severely limits cam choice without retarding to clear, which is a false economy mid range wise. Realistically, more than 1mm lift at TDC is risky without changing the pistons (and hence rods).
The PT81s are quoted as 1.65mm lift at TDC on 110 degree peak angle, which is risky, retarding it beyond 110 degrees is going to spoil the mid range; which makes it to my mind an excessive cam for the standard engine.


so all these PT81's are either running retarded and rather peaky, or stupid close to the pistons...

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Posted 7th May 2009 at 02:29
sandy

Junior User

Location: Truro

Registered: 02 Oct 2005

Posts: 70

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Post #4
Must be. Here's a couple pics of an engine I set up very carefully with 1.4mm lift at TDC, turned out the head had been skimmed 0.3mm, so that gives you an idea of the clearances involved:
See the "clean ring" around the inlet valves, where they've been rubbing

Said piston


Most cams go in retarded in reality, because of the way most people set them up, which is probably why most people seem to get away with it; or maybe there are slight manufacturing tolerances involved.
I set up alot of engines and this is the only one that this has happened to me. It's cost me a fortune to put right and the poor customer's lost alot of use of the car too, so I won't be fitting cams into any more standard GTI6 engines!
Posted 9th May 2009 at 14:17
welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

Posts: 25,817

Status: Offline

Post #5
Thanks for the input Sandy, I have done a little more reading up on 16v xu specs and it seems the older 1.9 and 2.0 16v engines have far greater clearances, which explains why there are so many more of them making a relatively easy 180bhp.

That 0.3mm skim is over what I think you said was the safe limit for them before you start getting too close to the valve seats (0.25mm from memory) so that would have been silly close on even a thicker gasket Sad

I'm wondering if its worth dropping my spare set of RFY S16/Mi16 rod and piston sets into a gti6 bottom end (which is pretty much identical in most ways bar minor details) and sticking the later head ontop with some lumpy sticks, as I know the static compression ratio is a touch higher without a skim and nicely over 11-1 with a skim, and enough space for more lift @ TDC, how much more I don't know yet...

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Posted 9th May 2009 at 15:05
welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

Posts: 25,817

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Post #6
so, I've just stuck the RFY piston+rod combination in and bought it up to TDC, then dropped my gti6 head ontop with a loose valve, placed a dial gauge as straight as I could on its top end and moved the valve up with a set of needle nosed pliers, I got a travel of 3.70mm Blink

add a 1.2mm gasket and you have 4.90 mm valve to piston clearance at TDC, enough space for some fairly lumpy cams Big grin

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Posted 10th May 2009 at 03:19
petert

Newbie

Location: Sydney

Registered: 18 Mar 2007

Posts: 38

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Post #7
But where is the piston crown in relation to the deck? It might have 9.5:1 CR!

Also, you can't simply add the gasket thickness, as the valves are inclined at approx. 60 deg. So you need to apply the sine (or cos) rule.

The gasket will also compress a bit. So it's best to torque it down a bit before dropping the valve.
Posted 10th May 2009 at 16:30
welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

Posts: 25,817

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Post #8
Right, I'll have to find a gasket Doh

My thinking was that the cutouts are at the same angle as the valves and hence lifting the head up by 1.2mm will place the valve in the cutout slightly differently, but obviously there's no substitute to bolting down with a gasket.

I never took maths any further than secondary so though I recognise sine+cos I haven't a clue what they are!

Going off all the data for both engines even though the RFY piston doesn't come up to deck it has a flat top and gives a higher compression ratio unless I've missed something daft!

Given that the RFY has a larger head chamber voulme (40cc) and the same gasket thickness (1.20mm), one would assume that the RFY piston has a smaller dish volume (though its a flat top, it sits below deck)

I've worked it out to be in the region of 10.9 with a gti6 head on top due to its smaller combustuon chamber volume (37.2cc, 36cc skimmed 0.25mm which takes it up to 11+)

so what have I missed then? prepared to fail epicly LOL

could always drop in an 88mm stroke crank and bring them above deck slightly...

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Posted 10th May 2009 at 19:06
welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

Posts: 25,817

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Post #9
anyone any ideas?

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Posted 16th May 2009 at 05:35
crossflow

Regular

Location: England

Registered: 21 Jan 2008

Posts: 159

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Post #10
Best way to do this if you are worried about piston to valve clearance is to measure the clearance for piston to valve and get a local machinest to machine the cut outs deeper. You want a piston to valve clearance of around the 0.080th mark which is 2mm

I can explain how to do the checks if you think you able to do them
Posted 16th May 2009 at 06:43
crossflow

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Location: England

Registered: 21 Jan 2008

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Post #11
and putting a head on with the piston at tdc is not the way to check piston to valve clearance. there a way to do it
Posted 16th May 2009 at 06:45
petert

Newbie

Location: Sydney

Registered: 18 Mar 2007

Posts: 38

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Post #12
That's correct. If you had 0.080" at TDC, there will be <0.070" in reality, because the clearance is closer at approx. 10 deg. before and after TDC, for exhaust and inlet.

If you wanted to be rough, allow at least 0.095" at TDC for inlet and 0.120" for exhaust. A professional would check the clearance from 20 deg. before to 20 deg after.
Posted 16th May 2009 at 08:28
welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

Posts: 25,817

Status: Offline

Post #13
thanks for the input guys.

I can't imagine why bolting a head down and measuring how far the valve moves up and down isn't the best way to do it, its a basic physical measurement?

What's the right way ?!


There aren't any local engine builders to me, only a few remanufacturers, plenty of machinists about but none that do engines Doh so I doubt they'd have a clue what I was on about LOL

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Posted 16th May 2009 at 14:45
crossflow

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Location: England

Registered: 21 Jan 2008

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Post #14
you need to dummy build the engine up. Put soft springs into one exhaust and inlet valve. then you need to set up the engine cam timing wise. Then as petert says get a timing disc onto the back of the crankshaft and then measure in 5 deg segmants from 20 deg before till 20 deg after you find that 5 deg before is normally the closest. You measure the gap by putting a dial gauge onto the top of the tappet bucket. push the valve down and measure the gap with the dial gauge. It simple enought to do but very time consuming.

Where are you based??
Posted 16th May 2009 at 16:14
welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

Posts: 25,817

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Post #15
right, just some more on what I've worked out and found out -

I've been looking at my collection of XU10 engine parts, namely a gti6 bottom end complete, as well as the top end inc 10 bent valves (hence avatar) a set of 2.0 Mi16 pistons and rods, and some Newmans cams.

Some quick measurements with a dial gauge showed that there is next to bugger all room in the standard J4RS piston for any worthwhile camshaft upgrades, but I remembered that I had a set of Mi16 rods and pistons about and that they have a deeper cutout and a flat topped piston.

This combination with the gti6 head gave something roughly like 4.9mm valve clearance unsure.gif plenty for some half decent cams, and what is a slightly higher than standard compression ratio if I'm not mistaken :wacko

now I can't seem to fathom what I've missed going through my workings out and what data I can find on both engines.

RFY engine;

40cc head combustion chamber,

10.4-1 compression ratio

1.20 mm gasket.

RFS engine;

37.2cc head chamber volume.

10.8-1 compression ratio.

1.20 mm gasket.

I've worked out that the RFY piston + rod with a RFS head would give somewhere in the region of 10.9-1 compression unskimmed, and low 11's -1 skimmed to 36cc from 37.2cc.

I do realise that they dont come flush to deck like the gti6 piston, but are flat topped, but I have heard that this allows the use of an 88mm crank to push the capacity up to 2044cc, that'll still have a fair amount of space @ TDC for some nice cams over the RFS piston.

going off the basic data above I worked out the RFS dish to be 6.64cc, and the RFY to be 5.99cc (not dished but has cutouts and sits below deck)

I found some information just now in a topic on here;

quote:

Block height = 234.8mm (At least we found it to be that when measuring)
Rodlength Xu10J4 = 152mm
Piston Compression height = 39,1mm
Half the stroke 86/2 = 43mm
234.8 - 152 - 39.1 - 43 = 0,7mm


Which means that in a standard XU10J4 the pistons sit 0.7 down the bore.
Adding the extra 1mm with the 88mm crank will make them sit 0.3mm over the deck..


So, if I use 88mm crank for a 2044cc build with no other changes, I'll have circa 42.5cc combustion chamber volume for a 13.0-1 compression ratio Shock

To be confirmed, but there would be something like 3.9mm total valve clearance, less 1.5mm safe running clearance you could maybe run 2.4mm Lift @ TDC pretty safely.

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Bring on the Trumpets.

Posted 16th May 2009 at 16:15
welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

Posts: 25,817

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Post #16
missed your post there, I'm in South Wales.

your process isn't too far removed to what I've done already

I don't know how I would fare with placing the Dial gauge to the bucket to measure valve movement as they are hydraulic and hence will compress a fair bit before moving the valve, hence why I did it directly on the valve stem.

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need a part number? get on here - http://public.servicebox.peugeot.com

Bring on the Trumpets.

Posted 16th May 2009 at 16:20
welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

Posts: 25,817

Status: Offline

Post #17
Here's a list of the first two cams from Kent and Piper, and the only stats I have so far for Newmans

PT80, 1.65mm Lift @ TDC, Full lift timed to 110degrees, only slightly less duration and peak lift than PT81, and a near standard exhaust cam, too close for comfort.

PT81, 1.65mm Lift @ TDC, Full lift timed to 110degrees. DITTO!

Piper BP270H 1.09mm lift @ TDC, 110 deg timing for peak Just about safe

Piper BP285H 1.82mm Lift @ TDC 108 deg inlet 110 deg definitely not safe!

Newmans PH2, 1.4mm @ TDC, Full lift timed to 110degrees. just about safe.

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Posted 15th Mar 2015 at 21:41
petert

Newbie

Location: Sydney

Registered: 18 Mar 2007

Posts: 38

Status: Offline

Post #18
My new GTi6 Stage I regrind:

1.40mm @ TDC, duration 215 deg. @ 0.050"
Posted 19th May 2009 at 16:58
welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

Posts: 25,817

Status: Offline

Post #19
thanks Pete, I take it that is designed for an otherwise standard engine? May take you up on one of those.

Definitely worth checking that a thicker gasket was fitted if the head has even been off I think for a road engine on standard pistons, never know how much people take off them, as illustrated by Sandy and his customers bad experience pictured above.

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Posted 19th May 2009 at 17:02
adam b

Seasoned Pro

Location: The Nam

Registered: 24 Jan 2006

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Post #20
Is 1.40mm not blinking close though? What are the duration/lift of the standard items?

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Posted 19th May 2009 at 18:20
welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

Posts: 25,817

Status: Offline

Post #21
yeah, though from Sandy's experience he said he was setting them to 1.4mm, which would have been fine had the head not skimmed 0.3mm Doh

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Bring on the Trumpets.

Posted 19th May 2009 at 18:58
dan gti-6

Regular

Location: Winchester

Registered: 26 Jan 2008

Posts: 112

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Post #22
welshpug! wrote:
yeah, though from Sandy's experience he said he was setting them to 1.4mm, which would have been fine had the head not skimmed 0.3mm Doh


If the head has been overhauled properly, a 'decent' remanufacturer would cut the seats to correspond with material skimmed from the face (within limits obviously). So if the head has been lightly skimmed its not always the end of the world, remember the valves would also be ground and the stems lightly ground.

Although from what i understand 81s are so close i wouldnt be happy with just chucking some in my engine. I expect the reason many people get away with it is because a mecanic is never going to time lift at TDC.

Why not just have the valve cutouts machined in your standard pistons? We do loads at work, any decent engineering firm should manage.

Posted 20th May 2009 at 22:38
welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

Posts: 25,817

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Post #23
How much do you think that would cost to your average punter Dan?

I'm not so keen about that as it would lower the compression ratio, not really ideal when you're upgrading cams which typically run better with more than the standard ratio Smile

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Posted 20th May 2009 at 22:48
brett-black-rallye

Senior User

Location: felixstowe

Registered: 28 Aug 2007

Posts: 573

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Post #24
how much ruffly would it be to have the pistons machined?

*edit* too slow lol
Posted 20th May 2009 at 22:51
mark-house

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Location: Bury St Edmunds

Registered: 07 Apr 2009

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Post #25
I can see this is a hot topic at the moment. I would be interested in the cost too.

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Peugeot 306 GTi 6
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1967 Mini Cooper
1990 Jaguar XJR 4.0
Posted 20th May 2009 at 22:57

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