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I've been moving the car in and out of the workshop for the past few months while I work on the other one and I noticed a while back that the tappets sounded a bit noisy, not sure when it started but it was quite noticable when reving it.
I checked the valve clearances tonight and number 2 inlet is 7 thou and number 5 exhaust is 20 thou.
The others are 4thou inlet and 6 thou exhaust.
I can just reshim them but I am concerned as to why the exhaust one in particular is so far out.
Could starting it up running if for a minute and then switching it off a few times (probably 20-30) cause the valve seat to coke up, it seems unlikely?
I would not re-shim anything without giving the car a good hard run at operating temperature. Unless you have reason to believe that you have chronic wear on one cam lobe or follower. This assuming that clearances were correct in the recent past.
Last edited by Glyn M Ruck; 01-03-2019 at 07:57 PM.
I would not re-shim anything without giving the car a good hard run at operating temperature. Unless you have reason to believe that you have chronic wear on one cam lobe or follower. This assuming that clearances were correct in the recent past.
Thanks Glyn,
I've given it a run and it's still the same.
I'm confident they were right when I built the engine as I was very particular about it having had issues on a previous build due to poor machining.
i am concerned that either the valve is jammed part open or the seat has dropped. I will do a compression test later to see what it's like.
Something is not right. A clearance going from 6 to 20 thou. Sticky valve, seat issue etc. Jag's cams are tough old buggers but a friend had a similar problem on one valve & it was a badly hardened cam follower/bucket that wore very quickly & stopped rotating. The cam survived & a new follower fixed permanently.
EDIT: Also make sure that you are getting decent oil flow to the cam boxes.
Something is not right. A clearance going from 6 to 20 thou. Sticky valve, seat issue etc. Jag's cams are tough old buggers but a friend had a similar problem on one valve & it was a badly hardened cam follower/bucket that wore very quickly & stopped rotating. The cam survived & a new follower fixed permanently.
EDIT: Also make sure that you are getting decent oil flow to the cam boxes.
Thanks Glyn, the follower is the original one and is unmarked and nice and smooth in the head (not loose just nice).
Just going out into the cold to do a compression test, if it isn't low I don't know whether to just shim it on the basis that if it happens again I will need to remove the head and deal with it.
Its a puzzler, especially as the engine only has around 100 miles on it since the rebuild.
Right so the plot thickens, i've done a quick compression test, cylinder 2 is registering 0 whereas cylinders 5&6 (numbering from the bulkhead) are around 160-170PSI.
I wonder if the valve has stuck down and when I've started it the piston has hit it, that would take some doing though as the head was rebuilt and everything was nice and free as you would expect.
Otherwise something has got stuck in it but if so where has it come from and what is it? I've ordered a boroscope to have a look in the cylinder to see if there is a witness mark on the piston but I doubt I will be able to get it to turn back up to look at the valve. It was only £6 from ebay but a friend bought one a few months back and it was really good.
Argh! Not what you wanted to see. Let's hope it's not a bent valve. Access to a boroscope is a big help. Best not to speculate ~ could be many things. At least with side draught carbs the chances of dropping something into the inlet is small.
I couldn't wait for the boroscope to arrive so have whipped the head off to find a bent valve, rather strangely there is not witness mark on the piston to suggest that this is the result of contact so its a mystery as to how its happened on a engine that has hardly been used.
As the stem is bent the valve only fits in the guide in one position (i.e. it won't rotate) and there is some play in the guide although I remember there being a little bit in it before I put it together (even though the guides were new).
I'm not sure now whether to just put a new valve in and lap it in or whether the guide should be changed.
The other valves all look fine so its just really odd.
Last edited by Homersimpson; 01-05-2019 at 02:26 PM.
One possibility could the head have been accidentally placed on a hard surface prior to installation causing a slight bend on the valve?
As you say there is no indication on the piston crown to suggest contact internally.
One possibility could the head have been accidentally placed on a hard surface prior to installation causing a slight bend on the valve?
As you say there is no indication on the piston crown to suggest contact internally.
I was very careful to avoid this when I built it having read a thread about someone who wasn't and bent the valves.
The odd thing is that i'm sure it wasn't there originally as I would have noticed, it was such a loud tap you couldn't fail to but the last time I drove it properly was July, since then all I have done is started it up and driven it in and out of the garage and it doesn't run well on the auto choke so I wouldn't have noticed it as I wasn't revving it and it runs rough.
My main concern now is whether to change the guide (again) or whether to try the new valve in it and if its ok put it back together as it is.
What a royal pain, is there any witness marks on the inlet valve, the only other possibility is the exhaust valve stuck and got clipped by the inlet valve opening, there should be very small witness mark on the seat side of the exhaust valve if that happened. (it could be possible for the inlet valve to have stuck too and the opposite happen but only one valve bent.
If that is the case, you need to carefully check the valve spring pressures under compression, not an accurate test, but you can use some bathroom scales and a drill press which would show only a comparison between spring sets, and not any true measurement, I assume you have standard lift cams installed and the valve timing was correct.
Glyn is correct in saying that you should be fine just fitting a new valve, the concern will be trying to work out what happened and knowing that it won't happen again. I would accurately measure the valve stem of the bent valve, and compare it to a couple of other exhaust valves, also check the valve guide as Glyn said for out of round and also the bore to ensure there was enough clearance.
As Glyn says if you cannot find any witness marks, this is difficult to solve and leaves the concern of it happening again, so check every detail for clearances, spring pressures and compare to other valve parts.
Examine both valves fully for any witness marks, they could be very small and let us know what you find. A random bent valve is a little concerning if you cannot find the cause.
What a royal pain, is there any witness marks on the inlet valve, the only other possibility is the exhaust valve stuck and got clipped by the inlet valve opening, there should be very small witness mark on the seat side of the exhaust valve if that happened. (it could be possible for the inlet valve to have stuck too and the opposite happen but only one valve bent.
If that is the case, you need to carefully check the valve spring pressures under compression, not an accurate test, but you can use some bathroom scales and a drill press which would show only a comparison between spring sets, and not any true measurement, I assume you have standard lift cams installed and the valve timing was correct.
Glyn is correct in saying that you should be fine just fitting a new valve, the concern will be trying to work out what happened and knowing that it won't happen again. I would accurately measure the valve stem of the bent valve, and compare it to a couple of other exhaust valves, also check the valve guide as Glyn said for out of round and also the bore to ensure there was enough clearance.
As Glyn says if you cannot find any witness marks, this is difficult to solve and leaves the concern of it happening again, so check every detail for clearances, spring pressures and compare to other valve parts.
Examine both valves fully for any witness marks, they could be very small and let us know what you find. A random bent valve is a little concerning if you cannot find the cause.
Hi Tilleyjon, there arn't any marks on the bent exhaust valve and I have removed the inlet to check today and its perfect. I ground it in slightly just to check and it produced a perfect circle on the back with only about 10-20 seconds of work which is what I would have expected as its only done 100 miles at most since they were redone :-(
I will check the other items above and see whether I can find anything, it will also be interesting to see what the new exhaust valve is like in the guide when it arrives.
05-18-2018, 03:41 PM
