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Oven vs gas torch
bikecarbfred - 27/11/17 at 06:24 AM

Which would be the best way and cheapest way to heat up for thermal expansion around the valve guide area on a cylinder head?

Kitchen oven or hand gas torch. Do you need to get it to 100C. Would sticking frozen guides in a head that hot cause any cracking

nick205 - 27/11/17 at 09:48 AM

Not something I've done myself.

I'd have thought heating the cylinder head in an oven would be better as it would apply the same heat to the complete cylinder head. My brain thinks heating a pretty localised area with a gas torch would do just that - heat the localised area, but not the rest of the cylinder head.

(others may well have actual experience or indeed different thoughts)

mcerd1 - 27/11/17 at 10:19 AM

I'd be more worried about warping the head - its definatyl the sort of job I'd send out to the specialist engine machinists / re-builders...

nick205 - 27/11/17 at 10:40 AM

bikecarbfred - where are you located?

I can recommend an engine machine shop in Winchester (Hampshire) if it's of any use to you.

loggyboy - 27/11/17 at 10:48 AM

I would go with oven to keep it more 'even' expansion.


quote:
Originally posted by mcerd1
I'd be more worried about warping the head - its definatyl the sort of job I'd send out to the specialist engine machinists / re-builders...

Suspect an engine reaches a fair amound more than 100degrees whilst running.

mcerd1 - 27/11/17 at 11:06 AM

quote:
Originally posted by loggyboy
quote:
Originally posted by mcerd1
I'd be more worried about warping the head - its definatyl the sort of job I'd send out to the specialist engine machinists / re-builders...

Suspect an engine reaches a fair amound more than 100degrees whilst running.


Yes - but it does that while being solidly bolted down to the block to hold its shape

bikecarbfred - 27/11/17 at 01:43 PM

In that case it's best to gas torch the area around the guides and push the frozen guides instead of heating the whole head and warping it without it being bolted.

Just had it skimmed too recently.

mcerd1 - 27/11/17 at 03:01 PM

quote:
Originally posted by bikecarbfred
In that case it's best to gas torch the area around the guides and push the frozen guides instead of heating the whole head and warping it without it being bolted.

Just had it skimmed too recently.


but its probably more likely to warp with a localised heat source than heating it evenly

bikecarbfred - 27/11/17 at 03:04 PM

Well i'll make sure im holding the blow torch evenly across the section
talking 100C for thermal expansion

02GF74 - 27/11/17 at 05:49 PM

quote:
Originally posted by mcerd1
quote:
Originally posted by loggyboy
quote:
Originally posted by mcerd1
I'd be more worried about warping the head - its definatyl the sort of job I'd send out to the specialist engine machinists / re-builders...

Suspect an engine reaches a fair amound more than 100degrees whilst running.


Yes - but it does that while being solidly bolted down to the block to hold its shape


So that would imply the machine shop either has a engine block for every possible engine or else some jig with holes for all possible head bolt hole combinations, somehow I can't see either is likely. I accept that I could be totally wrong.

Unless you have a sealed and insulated box you are dreaming if you think a blow torch can get a cylinder head up to temperature.

Oven should be able to do it.
Can't see that heating a head evenly in an oven to 100c will warp it but then I've never done it so again accept I can be totally wrong.

How much is the head worth and how much to pay someone who knows what they are doing, that should be criteria to decide to diy or not.

rusty nuts - 27/11/17 at 06:18 PM

I would stick it in an oven rather than a gas torch but have you thought about this properly? The valve seats will need recutting to make sure they are concentric with the guides, if you haven't got seat recutting equipment you'll have to take it somewhere that has . I have fitted several sets of guides on VW Polo's Golf's etc by using a steam cleaner to heat the head and freezing the guides then using a proper guide drift and a spacer of the correct height above the head to insert the guides before recutting the seats.

J666AYP - 27/11/17 at 08:49 PM

Oven for me. Turn the heat up/down slowly so that the core heats up with the rest of it. It's a thick slab of metal, it will take a while to get the heat uniform through the head.

Jay

bikecarbfred - 27/11/17 at 08:56 PM

How hot did you get it with the steam cleaner.
the guides are out now so no choice but to put the new ones in. I took advice from some one who said I would be daft to put the valves in without new guides. I wish I hadn't.

If I do it carefully , hopefully I just need to lap the valves in on the seat.

perksy - 27/11/17 at 10:49 PM

I'd let an experienced engine/engineering shop do it

What happens if you don't get the temp correct and your halfway through fitting the guide/s and it goes tight?
You might well end up poo creek without a paddle

Tis your engine though so your choice

Have you checked the valve seats for damage?
You might end up having to have them re-cut, 3 angle valve seats might be the way forward depending on spec etc

hearbear - 28/11/17 at 12:29 AM

quote:
Originally posted by perksy
I'd let an experienced engine/engineering shop do it

What happens if you don't get the temp correct and your halfway through fitting the guide/s and it goes tight?
You might well end up poo creek without a paddle

Tis your engine though so your choice

Have you checked the valve seats for damage?
You might end up having to have them re-cut, 3 angle valve seats might be the way forward depending on spec etc


Just what I was going to say as I was working down the post. A guy I worked with tried something similar with a bushing on a tractor heated the rear of the gearbox casing and the bush in the freezer overnight, bush got halfway in and the heat over took the frozen bush and took a hold which left a bush half in and solid. We did get it in eventually after heating the housing again and emptying a few CO2 extinguishers in to bush to contract it enough to to move. I would second getting a machine shop to do it for you.

bikecarbfred - 28/11/17 at 06:36 AM

Have tried it with another head that's out of use.

Valve just go in and the angle is right because it ride against the angle of the hole . pop valve in and just lap the seat with the valve,

did not realize what the fuss was about. The guides came out easy enough. the hole has the right angle. new valve is flush against seat and in centre. did i get lucky? drift tool and hammer. never heated the head at all.

hopefully all 16 on other head go alright.

It's only a small block 1.4.

rusty nuts - 28/11/17 at 06:26 PM

You'll find out if you get it running. I once wasted half a day looking for an intermittent misfire , eventually found it was a floating valve guide.

bikecarbfred - 28/11/17 at 07:58 PM

True.

If it happens it's going to be on the exhaust size because of the immense heat and the expansion. If I even get that far then after I have run in the new camshafts in. I'll take off the exhaust manifold n check if any have budged.

Cheers for the concern guys.