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Author Subject: Kent PT 81
b11 bob Banned!

Location: birmingham

Registered: 19 Dec 2010

Posts: 265

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Post #1
When fitting PT 81 to a normal head one that has not had a skim can these cams be fitted some say yes some say no others just go off topic whenever this gets discussed on here.
So sorry to sound so crude but can we just get to the point on this please. Can these be fitted without the valves hitting the pistons ? If the valves hit the piston when fitted what is the best measure to take or is there a combination of measures that need to be taken.
Do i need to machine the pistons? if so by how much ?and what sort of costs are we looking at to do so ?
Or would fitting a thicker head gasket be a better option

I personally think that machining the pistons to allow valve clearance would be the best option but would like to know how much in mm i need to machine the cutouts by.Has anyone on here done this a chap called Welshpug had a thread on here about this but that like many threads on here went off topic and ended without the initial query being resolved i tryed to send him a pm but cannot get to him anyway can anyone out there advise me on the best way forward with this please thank you

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205 GTI6 235 bhp at 7400 rpm
Posted 4th Sep 2011 at 18:54
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welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

Posts: 25,839

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Post #2
have a read of my thread, all the info is on there, pt81's are pretty marginal but still not that much wilder than stock.

might as well get the pistons done and run something a little longer duration imo Smile

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Posted 4th Sep 2011 at 19:39
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b11 bob Banned!

Location: birmingham

Registered: 19 Dec 2010

Posts: 265

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Post #3
welshpug! wrote:
have a read of my thread, all the info is on there, pt81's are pretty marginal but still not that much wilder than stock.

might as well get the pistons done and run something a little longer duration imo Smile


What would you recommend ? if i get the pistons done could i run pt 82 cams ? i dont really want to go onto solid lifters etc i would like to retain the original head set up

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205 GTI6 235 bhp at 7400 rpm
Posted 4th Sep 2011 at 23:08
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daveyboy

aka Jim Davey

Location: Southampton

Registered: 01 Oct 2007

Posts: 8,648

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Post #4
PT82 can run with hydraulic lifter no problem. The machining is critical though. It needs to be done by someone highly skilled and familiar with engines (not just any old machine shop) you are bsst speaking to someone like Sandy on here who has done this op before. He will want your cams and the engine so he can mark the valve postions relative to the pistons with a centre dot, than he can do the machining (valves will want at least 1.5 mm of radial and 2-3mm of vertical clearance) and then dry build and check the clearances with plasticine or similar and physically confirm you have the required clearance. It may be worth getting forged pistons that raise CR and garantee clearance though as by the time you pay for pocketed pistons and gaskets etc you will have spent a fair few quid. I would save a little longer and get a bigger power hike with pistons and rods. Just my opinion though.

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Posted 5th Sep 2011 at 13:25
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welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

Posts: 25,839

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Post #5
if its stock valves etc then Sandy (or colin actually) dont need anything more than the Piston + rod as they have a jig for this operation now, as does Martin ( crf_450 )

martin only charged me £80.

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Posted 5th Sep 2011 at 15:06
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daveyboy

aka Jim Davey

Location: Southampton

Registered: 01 Oct 2007

Posts: 8,648

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Post #6
Thats not bad at all, is there enough clearance for PT82s as well as 81s?

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R H Davey Welding Supplies. I sell new and used welding equipment in the Hampshire area. I take on welding jobs in the evenings, ally casting repairs are one of my specialities but I can weld pretty much anything. PM me with your requirements.

Some of my services: (See my for sale threads)
Engine mount/chassis repair
Solid Beam Mounts BACK IN PRODUCTION
Harness bars
Posted 5th Sep 2011 at 15:59
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welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

Posts: 25,839

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Post #7
PT82's are 2.03mm lift @ TDC, Martin does the cutouts 1mm deper than std, I can't remember specifically how much clearance there is as std and what the tolerances were but a few engine builders were running up to 1.4mm in stock engines.

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Posted 5th Sep 2011 at 16:50
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Denis

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Location: Cambridge

Registered: 07 Sep 2004

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Post #8
Firstly, what a lot of people do not realise when fitting performance cams you time them from the manufactures spec and not standard timing mars.
So, PT81s will work fine on standard timing marks, but won’t make full power as they need to be advanced relative to the marks. When timed correctly – it is highly likely that they will touch the pistons (there were marks of piston to valve contact in my engine).
If you want to know the exact measurements for particular engine – you have to do dry build and measure it.
The standard inlet cam has about 0.8mm lift at TDC vs 1.64mm for PT81. So you would need to deepen the cutouts by about 1mm to keep the same amount of clearance as standard. Which is what was done on my engine by Martin, (CRF450).

Of course, in ideal case I would deepen the cutouts a bit more and get the head skimmed to up the compression ratio slightly from standard to compensate for the material removal from pistons and work with increased duration of the cams...

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Posted 5th Sep 2011 at 18:28
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b11 bob Banned!

Location: birmingham

Registered: 19 Dec 2010

Posts: 265

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Post #9
russian guy wrote:
Firstly, what a lot of people do not realise when fitting performance cams you time them from the manufactures spec and not standard timing mars.
So, PT81s will work fine on standard timing marks, but won’t make full power as they need to be advanced relative to the marks. When timed correctly – it is highly likely that they will touch the pistons (there were marks of piston to valve contact in my engine).
If you want to know the exact measurements for particular engine – you have to do dry build and measure it.
The standard inlet cam has about 0.8mm lift at TDC vs 1.64mm for PT81. So you would need to deepen the cutouts by about 1mm to keep the same amount of clearance as standard. Which is what was done on my engine by Martin, (CRF450).

Of course, in ideal case I would deepen the cutouts a bit more and get the head skimmed to up the compression ratio slightly from standard to compensate for the material removal from pistons and work with increased duration of the cams...
So if i get Martin to take 2mm of the piston valve cut out i could then skim the head 1mm which would give me a gap of 0.16 mm is this feasable surely i will get the best of both worlds doing it this way no valve to piston contact and more compression ratio than standard thats if i go for pt 81 cams

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205 GTI6 235 bhp at 7400 rpm
Posted 5th Sep 2011 at 21:26
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welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

Posts: 25,839

Status: Offline
Post #10
you can't skim the head 1mm, 0.25mm is safe max.

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

Bring on the Trumpets.

Posted 5th Sep 2011 at 22:23
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b11 bob Banned!

Location: birmingham

Registered: 19 Dec 2010

Posts: 265

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Post #11
welshpug! wrote:
you can't skim the head 1mm, 0.25mm is safe max.
So how thick is the standard head gasket ?

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205 GTI6 235 bhp at 7400 rpm
Posted 5th Sep 2011 at 22:35
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welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

Posts: 25,839

Status: Offline
Post #12
1.2mm iirc, repair gasket is 1.4mm

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Posted 6th Sep 2011 at 02:53
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allanallen

Seasoned Pro

Location: Buxton

Registered: 01 May 2007

Posts: 1,399

Status: Offline
Post #13
I wouldn't make the cut outs 2mm deeper, gti6 pistons haven't got the thickest crowns. I'd work on 1mm being the maximum and as pointed out it's proven to be safe by several people on here including myself.

Al

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Posted 6th Sep 2011 at 06:12
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allanallen

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Registered: 01 May 2007

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Post #14
Double post

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Posted 6th Sep 2011 at 06:27
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daveyboy

aka Jim Davey

Location: Southampton

Registered: 01 Oct 2007

Posts: 8,648

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Post #15
Don't take anything for granted, do the dry build with the cams timed at their recommended settings and physically check the clearances. You certainly don't want any less than 1.5mm of vertical clearance at any point in the cycle, valves at high rpm can stretch slightly as well as expanding with heat, add to that a little 'valve float' with a badly timed gear change or missed gear entirely and you will get piston to valve contact if you run less than a millimetre gap. It's the builders responsibility to do the checking, not the machinist and there will be no comeback if it destroys itself because you did'nt measure something. If you are unsure of any of the operations bieng discussed I can reccommend a couple of very good books on the subject, that way you will be well informed when talking to your machinist and be able to get exactly what you want.

________________________________________

R H Davey Welding Supplies. I sell new and used welding equipment in the Hampshire area. I take on welding jobs in the evenings, ally casting repairs are one of my specialities but I can weld pretty much anything. PM me with your requirements.

Some of my services: (See my for sale threads)
Engine mount/chassis repair
Solid Beam Mounts BACK IN PRODUCTION
Harness bars
Posted 6th Sep 2011 at 13:27
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