Nooooo! Loose VH exhaust guide disease strikes...
Posted: Fri May 19, 2023 12:23 am
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.
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....!)
SG
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.
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....!)
SG