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Cylinder Head Advice Wanted


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13 replies to this topic

#1
dawning

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I have my cylinder head off my XS at the moment, it needed new valve stem seals. I am hoping to get some opinions on what work I should carry out while the head is off. The engine has 104,000 miles on it, and was running well apart from being smokey when starting and under hard acceleration. My original plan was to lap the valves, replace all the gaskets, and oil stem seals.

Having tried to clean up the cylinder face I am unable to get it spotless, ive done some more reading it seems I should probably skim the head anyway, although its not conclusive. I would rather avoid spending money pointlessly but if its generally considered to be the right way to go I would rather get it skimmed, any opinions welcome.

Some of the exhaust valves where coked up on the stem, one of them refused to spin round while lapping, I gave it a good clean and lapped it in but I think it might be time to replace the exhaust valves (quite cheap on ebay) does replacing the valves mean I should also be getting the seats re-cut? It was my first attempt at lapping valve and after about 5 minutes on each one with a fine paste they are looking ok although some are still a bit pitted. 

Should I be thinking about replacing the valve stem as well? I think these are still available from peugeot. 

Should I replace the valve springs even if they are all the same length? 

My aim is to make it reliable and feel confident driving it hard. 

 

Sorry for the poorly worded questions, hopefully someone can help, not really sure on the life expectancy of these parts in a TU engine, 

 

Thanks



#2
DamirGTI

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Check the valve guides , if there's too much play in the guides should replace them .

Stem seals - defintely replace

But , when replacing guides the seats must be recut afterwards , also if fitting new valves . But do measure the valves with micrometer as they're pretty hard thus the valve guide wears out more often than the valves .
Best to get the head base skimmed cos it might be uneven/twisted and you'll struggle to get the required finish doing it by hand/sanding paper .

D

#3
Tom Fenton

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Whilst it's off, do it right. Take it to a machine shop if you can't measure it accurately yourself. I would suggest at 100k it's quite probably getting ready for valve guides. When these are changed the valve seats must then be recut to suit the new guide position.

#4
toolie72

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Do you know how to roughly check guides? Online Haynes manual will explain it
If you just replace seals and guides are knackered then new seals will not last long as valve rattles about
If valve guides are replaced you have to recut seats-simple as that. They never quite line up with old seats.

I got my head refurbed (1.9) before Xmas and it cost me £180 (cash-no receipt!)- that was clean,skim,new guides and recut seats
I'm a toolmaker to trade and I was happy with quality of work done (of course if I had machines still, I could do better!guffaw)
Bang an email out to your local machine shops asking for skim price, refurb price etc

#5
dawning

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Thanks for your replies, it's really helpful.
I took the head to be skimmed at a place called classic and modern in Bracknell, 35 for a reface although there is a deep spot of corrosion on one end of the head face between two water ways which he said might need welding. I ordered 3 exhaust valves off eBay , in Peugeot boxes 7 quid each hopefully they are legit, only 3 available or I would have got 4. Going to get new springs and guides from Peugeot today. He quoted me 120 +vat for replacing the guides and cutting the seats, seems reasonable but I want to get it done right. I've not read any reviews of their work online and I'm not sure what they cut the valve seats on. When I've searched about valve seats it keeps coming up with 3 angle discussion, I will talk to the engineer about it when he phones me about the cylinder head. Thanks again for the input!

#6
Tom Fenton

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Personally I would let the machine shop source the parts. They will be just as good and probably cheaper than Peugeot direct. Valves can be re cut also and so won't definitely require changing.

#7
toolie72

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Three angle is purely for flow of air/fuel mixture. At one time you'd radius valve and leave say 1mm of angle on the valve, great for flow but perhaps not best for longevity as your actual mating surface is smaller
Nowadays the same result can be done with three angles giving pretty much the same result but valve contacts more of seat when shut so should last longer but still give you maybe 1 bhp per litre (no warranty implied haha) depending on engine type etc

#8
DamirGTI

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If going for a multi angle seats , can tell you which angles works best for TU heads .

 

Factory cut seats at 30 deg. on these heads are hopeless for flow .

 

 

D



#9
And

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Most XS valves are cut at 45deg same as all the other TU's it was only some of the early TU5 that had 30deg inlets but the exhaust was still 45deg the later ones changed back to both been 45deg.

#10
dawning

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Great info, thanks all. Peugeot said 20 quid per stem :0 was shocked ! Would be great to know the best angles for a tu. not spoken to the engine place yet, I do hope they know what they are doing!

#11
DamirGTI

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Good quality guides and seals/gaskets can be found aftermarket .. no need for OE parts unless you want to pay extra for the PSA package , same ones you can find in most car part stores just pick known good brands : goetze , elring , victor reinz , payen , corteco ... AE or freccia (for the guides , if the machinist doesn't have them i.e. you need to buy them yourself) .. personally would insist on fitting/buying bronze guides , and avoid cast iron guides .

 

 

Seat angles (both inlet and exhaust) : 45deg. x2mm. (main/contact seat) and 70 or 75deg. (bottom seat under the main 45 ) .. also do the 45deg. x2mm. main cut on the valves too . All angles cut sharp and left sharp , not radius !

 

 

D



#12
And

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I would fit a genuine head gasket tho when it comes to re fitting, they are not much more cost wise and form my experience and sure a few others they are more reliable.

#13
drmo

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These engines are cheap as chips when it comes to rebuilding.

 

A few pointers:

 

 - get the head to a good machine shop! I mean it. Do it properly and recut the seats (30/45/60 is a good starting point and you can't get it wrong with that on these heads. 75deg undercut is better on these heads, but not all the shops can do it). Lapping the valves is a "stone age" process which is also harmful for the seats and valves, as the particles from lapping paste stay in the seat and damage it over time.

 

 - Resurface the head. It will probably need only a minor skim (0.05mm) if it is not warped so that the cam timing won't be that way off.

 

 - here is a way how to check valve guide clearance:

There is a formula for calculating the clearance of a rod in a bushing (valve in a guide) where one end of the rod sticks out from the bushing by any distance and you measure the rock at that end of the rod. Simple diagram below.
 

==G==
=====V===
==G==


G = Length of the valve guide
V = Length from the end of the valve where you measure the rock to the opposite end of the guide.
R = Amount of rock
C = Clearance between valve and guide

C=(R*G)/(2V-G)

As you can see if you measure the rock exactly at the end of the valve guide then G = V and the formula simplifies to C = R which is fairly obvious.

source: http://www.pistonhea... work&mid=75913

 

You don't need to buy OE valve guides, you can get Freccia which are really good and not that expensive.

 

 - U can use Elring head gasket. It is cheap as chips (probably around 10gbp in any store). I also advise you to use new head bolts. Also from Elring they are really cheap. The same goes for valve seals (Elring are good and cheap).



#14
dawning

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Thanks for all the replies. I had the head to a machine shop and it got a skim, after tom fenton saying I should get the valves and seats reground and the guides replaced I asked the machine shop if they could do it but he said its too late as there is a high chance of damaging the face in the process, I had no idea about that but I guess it is true. Looks like im going to have to just give it a lap and hope the guides are ok! I think the machine shop was good, couldnt find any reviews online but it was the cheapest skim I could find (£35+vat) fairly localy. I will check the play in the valves and try and get my head round that formula, thanks drmo

I have a gasket kit from elring, heard a few people saying that its worth getting a pug head gasket, hmmm decisions...

Also got a broken spacer on the camshaft thurst fork which doesn't appear on service box which is annoying but im sure I will find somthing, I will try and get a picture up.