plentywahalla
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| posted on 19/6/12 at 07:41 PM |
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Skimming the head
A mate has asked me to help him fix his engine. Its a Volvo V70, 2.5 litre turbo 5 cylinder.
His problem started when the water pump went. It acts as a tensioner for the cam belt, and when the belt went slack it jumped a few teeth on the cam
pulleys and several of the valves are bent. That is what I assume as a compression test shows no compression on two cylinders and only 50 psi on two
others and 130 on the 5th.
Everyone in the trade he has spoken to get quotes says the head needs to be skimmed. We are goping to do the job ourselves so I want to know why does
the head need skimming? There has been no overheating to shouldn't be any distortion.
Rules are for the guidance of wise men ... and the obedience of fools. (anon)
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theconrodkid
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| posted on 19/6/12 at 07:46 PM |
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check the head with a straight edge,i never had one skimmed unless it needed it
who cares who wins
pass the pork pies
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britishtrident
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| posted on 19/6/12 at 07:54 PM |
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Sounds much more like a valve problem. A cylinder leak down test or remove the head and turn the head (without manifolds) on its side,
fill the ports with kerosene and see how much the valves leak.
When I overhaul heads i do the above refitting and in addition if no obvious leaks the next stage is to direct a jet of compressed air round the
edges of the valve, any tiny bubbles that show up in the ports indicate the valves need more atention.
[Edited on 19/6/12 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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big_wasa
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| posted on 19/6/12 at 07:55 PM |
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If it didnt get hot it should be straight. The valve damage may be another matter.
The last one I got skimmed was £30 cash in hand, I took my mates in and they charged him £25, jammy git.
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dray13dad
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| posted on 19/6/12 at 07:59 PM |
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Yep sounds like valves,but would also have a good look at the cams as year unknown they do use hollow tube basicly for the shaft and then press the
lobs on,when belt goes can push lob round on shft,also can tend to twist/distort shfts so make sure are true and run free in head.would always skim a
head when it has been removed..
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Ben_Copeland
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| posted on 19/6/12 at 08:13 PM |
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I've had loads engines apart. Had a cam belt go on my Vauxhall engine. 8 out of 16 valves bent, valve guides broke. Replaced them. Didn't
skim head as it didn't need it. I wouldn't ever skim a head unless it was warped.
Ben
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Ninehigh
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| posted on 19/6/12 at 08:41 PM |
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They could mean just scrape it, make sure you get all the gasket off before you stick the new one on...
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cliftyhanger
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| posted on 19/6/12 at 08:55 PM |
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The garages are thinking the "just in case" argument. If it costs an extra £30 or so it is very little in the overall bill, and belt and
braces. And may well not be needed.
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degmwilliams
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| posted on 19/6/12 at 10:21 PM |
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I do head skimming if your interested in having it done
Building a tiger Avon st170 (slowly)
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owelly
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| posted on 19/6/12 at 10:26 PM |
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I'm another 'don't skim if it don't need it' guy. But, if there is any doubt, then skim it. Most machine shops should
check it for you for a couple of quid in the tea fund.
http://www.ppcmag.co.uk
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plentywahalla
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| posted on 19/6/12 at 10:51 PM |
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Thanks everybody .... I think I will check it thoroughly with a straight edge and make the decision based on what it looks like.
I think the logic from the garages viewpoint is, it is an insurance policy for them and they can get the customer to pay 30 quid for it.
Rules are for the guidance of wise men ... and the obedience of fools. (anon)
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snapper
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| posted on 20/6/12 at 04:50 AM |
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Iron or ally head?
If ally just getting the old gasket off means the head needs refacing.
For a few quid why not?
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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Mr Whippy
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| posted on 20/6/12 at 07:23 AM |
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skimming the head will change the compression ratio. Total waste of time if it's just a timing gear issue, a good steel rule placed over the
head will show any dips
Saying that I have worked on an overheated volvo engine which also had no compression and that head was distorted, if you are not doing the work
yourself then you will be at the mercy of the garages. Apart from a rediculous amount of bolts and nuts the top end was very straight forward. The
head needs to come off regardless and the damage inspected
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