valve guides

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bill.bottrill
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valve guides

Postby bill.bottrill » Mon Dec 24, 2018 5:08 pm

Hi,
I have started to build up my square 4 mk1,I should like to replace the valve guides.Has anyone had a go at this on the forum,is there any notes about, what temp should I take the oven up to,
I checked in Waller (I eventually found my copy) he says the springs hold the guides in place! but that's about it. It doesn't look like that on the ones I have! (there are two types for the mk 1)
I can see you can drive them down to a collar,is that it, do they hold in just by the tolerances. Is it ok to drive them out (with the head hot) with an aluminium drift made to go over the guide
I'll put the new guides in the fridge ofcourse,do they go in easily then, is there anything to be careful of. regards bill

Gui.dorey
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Re: valve guides

Postby Gui.dorey » Fri Dec 28, 2018 7:37 pm

Hi Bill,

Did the same not too long ago,but be prepared for a lot of foul language.

I put the head in the oven at 150C and was able to drift the old guides out without too much trouble. The new ones were from Drags and they are a tight interference fit. Head back in the oven and the guides in the ice box. Then smeared everything well with light oil and drifted them in. It took a lot of pounding and I was afraid of cracking the head, but in the end they all went in. After finishing, I did have to slightly ream the guides and file the top edge a bit as they were not immune to my pounding.

Before you proceed, you might want to wait for a few more answers as there might be a smart bloke around here who has a better method, but that's the way I did it.

Cheers,
Gui

bill.bottrill
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Re: valve guides

Postby bill.bottrill » Sat Dec 29, 2018 10:37 pm

Thanks Gui,
I will be meeting up with the guy who helped me build up my mk 2 in the next couple of day's,so I will double check with him also.I thought they were just pressed in, there isn't any forces on them but the other set for the mk 1 are held down by the spring so I thought there might be another locking device used.
I'm not so far ahead as you with the build,but I checked the pushrods length 147mm/146 approx, my guides look very similar to the photo on your other post,however the tops of the guides are very different to your's, the one's in the head have convex tops also the new ones, your's look concave at the top! they are 12mm from the raised base anyway.
I would say be very careful how you build these engines,they leak like a sieve,if you take any short cuts you will pay for it later,I've built other bikes no real problems,there's more oil and petrol under my mark 2 than in it I have had the tank off twenty times before I stopped the petrol leak!
I notice you said you haven't fitted the timing chain yet,have you tightened up the camshaft,on my engine the shaft locks up if it isn't tight as it jams on the case.It's very close but once it's tigtened it's quite free cheers bill

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Re: valve guides

Postby Gui.dorey » Sat Dec 29, 2018 11:09 pm

Thanks Bill,
There are two different guides for the MkI, but I have the correct ones for my engine. There's a description of the difference on the Draganfly catalogue. You can check online under MkI head on their web pg. The top of my guides isn't concave - it might just be the picture that appears that way.
My camshaft moves freely either tightened or loose. Where is yours catching? Are you sure it's supposed to do that?
The guides are not held by anything. They are just an interference fit. I believe the earlier ones had also a lower spring collar.

ralph thetford
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Re: Fitting valve guides

Postby ralph thetford » Fri Jan 04, 2019 8:38 pm

I have just fitted a set of guides to my 1938 square 4 iron head ---I purchased a set of guides from Dragonfly which were 2 thou over the size of holes in the head which is really too much for the guides diameter ----After very helpful feedback from this forum I reduced them down to --size of hole plus 0.0007" (7/10 of a thou) I did this in the lathe using emery paper ---I then put the guides in the freezer overnight a next day heated the head up in the cooker to 120 centigrade and then hammered them in using a stepped brass punch------ It all worked well--the guides are very tight in the head and went in without brute force.

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Re: valve guides

Postby roger.fellows » Fri Jan 04, 2019 8:47 pm

Bill, do you have the stepped washer in place on the camshaft?

bill.bottrill
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Re: valve guides

Postby bill.bottrill » Sat Jan 05, 2019 6:32 pm

Sorry for the late reply,my son has just come over from ireland
Thanks Ralph,that's just the info I need,I didn't want to replace the guides, but the mk 2 smokes so much on tickover I thought I had better start with new for the mk 1,is it possible to put small rubber rings on the valves to stop oil drain or will they just crunch up! I will carefully check out the size between sets,as these new ones just came off ebay.
Roger, i think I can remember putting on the stepped washer,I had left it on the shaft so I knew which way round it was fitted.
When I fitted the camshaft you could slide it side to side (n/s to off/side) just abit.
when it was pushed towards the nearside crankcase it locked up maybe 90 degree freedom,it appeared that the cam lobe hit against the case,once the cog was on in the timing chest the shaft was pulled over and was in line and quite free.
I didn't much like this but didn't want to distube these 68 year old cases too much! because the off side cam bearing machines out most of the thickness of the crankcase off side, so there is only a small amount to stop the bearing passing completely through.(what a cr"p design)
Well i suppose there isn't any side forces on this to allow it to push through but I would have liked some sort of spacer to fill the gap on the shaft n/s!
I wonder if anyone has an open engine and could see if this fouling is common with the cog off. bill

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Re: valve guides

Postby roger.fellows » Sat Jan 05, 2019 6:43 pm

There are various threads concerning the oiling problem on the forum. David Anderson has suggestions about it, including some sealant at the collets and the use of Viton rings, but I'll suggest somebody else might post links/quotes - I'm behind on that sort of thing. Might be worth putting 'oiltight' in the search box.

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paul.wirdnam
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Re: Fitting valve guides

Postby paul.wirdnam » Sat Jan 05, 2019 8:53 pm

ralph thetford wrote:I have just fitted a set of guides to my 1938 square 4 iron head ---I purchased a set of guides from Dragonfly which were 2 thou over the size of holes in the head which is really too much for the guides diameter ----After very helpful feedback from this forum I reduced them down to --size of hole plus 0.0007" (7/10 of a thou) I did this in the lathe using emery paper ---I then put the guides in the freezer overnight a next day heated the head up in the cooker to 120 centigrade and then hammered them in using a stepped brass punch------ It all worked well--the guides are very tight in the head and went in without brute force.


Ralph, I guess you must have bought those sometime ago...as Drags are out of stock on guides for my '39 4G and it's the only thing holding me up on my engine build. I don't think Bruce sells guides, only the valves which I've bought from him.

After knocking them in, are you going to chamfer the head of each valve to help keep oil away from the stems?
'28 Model B (future project), '30 Model F, '31 SF31, '35 4F, '38 VB (abandoned project), '39 4G (current project), '46 VH, '48 KG

Paul


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