Nooooo! Loose VH exhaust guide disease strikes...

pictures (or stories) of hideous injuries sustained by your ariel
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Simon.Gardiner
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Nooooo! Loose VH exhaust guide disease strikes...

Post by Simon.Gardiner »

Well, my turn now.

Decided the VH was getting a bit too noisy (despite still going well, not obviously burning oil and still supporting a good long stand on the kick-start) so pulled the top end apart.
Found a very wobbly exhaust valve (even with the valve springs still in place), which on further investigation wasn't the valve moving in the guide but the guide slopping about in the head.
I fitted new inlet and exhaust guides (and valves) 8k miles ago; it was checked out 5k miles ago (with the exhaust valve getting a brief re-grind) and the guide was quite firm then. Grrrrrrr. :roll:
The guides (to the best of my knowledge) were both N.O.S Ariel parts that I'd been carefully hoarding for several decades.

This issue has had a few mentions on the Forum before now, and David Anderson put up a short thread on his experiences back in 2016.
viewtopic.php?p=37648
My head (push-in pipe type) seems to have more meat around the exhaust guide than David's (I think my head has 18mm support over the length of the guide, David gives a figure of 12mm for his head). Also, looking at the photo of David's head (in the topic I've linked to) my head might have more metal under the spring seat, although it's difficult to see the exact edge of the machined area in Davids pics (and in mine the indent that the locating collar has made makes the machined area look narrower than it is).

A bit puzzling to me is the appearance of the exhaust guide, which looks to have been corroded in places (see pic) and that it's reduced in outside diameter, where it's been in contact with the head, from 0.627 to 0.618 (this is pretty uniform along the entire length under the collar).

The bore in the head is a couple of thou oval (front-back) and the collar on the guide has indented it to about 0.05" , so as well as getting bored out for an oversize guide I think (in the interests of keeping the maximum possible support for the length of the guide in the head) I'm going to need that indentation filling in with weld.

I think this engine's going to be out of commission for the summer (which will probably please the BM....!)
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SG
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'55 Huntmaster, '56 VH, ' 51 VH, '62 Arrow, '80 R100RT, '00 Sprint ST (now with a new Arrow project, and just now those 4-stroke Ariel parts can't even make one running bike...)
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paul.jameson
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Re: Nooooo! Loose VH exhaust guide disease strikes...

Post by paul.jameson »

This is all too common a problem on alloy head VHs.

But it rarely happens on a Square Four, despite the larger number of valve guides! (As Square Fours have come in for criticism elsewhere on the Forum recently, I am taking the opportunity to say they do have some advantages.)
Paul Jameson
35 LG (project), 37 RH500, 52 ex ISDT KHA, 54 KH(A), 75 Healey 1000/4.
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist (but not Machine Registrar), Gauges and Clocks Spares Organiser.
Simon.Gardiner
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Re: Nooooo! Loose VH exhaust guide disease strikes...

Post by Simon.Gardiner »

As noted by Nev in the post that's now been moved to 'Top end troubles'
nevhunter wrote: Sat May 20, 2023 12:53 am .....The original bronze one is very eroded so something's "different" there....
Something's obviously very different, I was hoping someone might say they'd seen that sort of thing before and knew what the cause was!
Rightly or wrongly I've discounted anything wrong with the oil 'cos the inlet guide isn't the least bit eroded/corroded top or bottom.
Also the exhaust valve itself looks in reasonable nick, it's still a good fit on the guide and the face isn't any worse than anything I've seen previously.
There was no aroma of cooked oil that I've sometimes noticed when I've taken the exhaust rocker box off an iron head single, but that might be down to the oil (this engine has been run exclusively on Miller's Pistoneeze 50). However I'm not sure why there's some staining on the head, under the spring seat.
I'm also curious about why the guide has reduced in diameter so much ( and apparently uniformly) where it's been in the head.
Maybe I should see if someone can do a material analysis on it....

SG
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'55 Huntmaster, '56 VH, ' 51 VH, '62 Arrow, '80 R100RT, '00 Sprint ST (now with a new Arrow project, and just now those 4-stroke Ariel parts can't even make one running bike...)
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Re: Nooooo! Loose VH exhaust guide disease strikes...

Post by nevhunter »

Does the motor ever get started in the shed and then left for a while without a long run. THAT will cause condensation. The guide being loose in the head may make it run hotter is another possibility. When you sleeve a motor you allow more piston clearance because of reduced heat transfer through the sleeve/cylinder boundary. . I have 3 or4 Bronze guides here all of which have come loose and none of them are as eroded as your's is and a couple are over the BOOK size on the OD. This is a pretty common problem with some alloy heads. Nev
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Re: Nooooo! Loose VH exhaust guide disease strikes...

Post by david.anderson »

While I do not wish to jinx myself, my head repair mentioned above and in viewtopic.php?p=37648 is still holding up. The head is fitted to my short stroke VH and has done a bit of hard track work at up to 8000rpm, but is now retired to road use.
I have subsequently been given another VH alloy head, which clearly had a loose exhaust guide, that someone has made a bad attempt at boring out. Sometime early next year when I start yet another VH project, it will be getting the same treatment that I gave the prior mentioned head.
David
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