24 years restoring a Sprint in New Zealand

[Jon Tilson]

I agree with Jeroen. James (Knightrider) had a similar engine issues when IIRC something from a K+N air filter was ingested and damaged a piston.

It looks like you should be sorted with a new valve and guide and some grinding in.

Jonners

[straylight]

thanks jeroen and jonners....I really should think a bit more before I rush in and post eh ?

stu

[Robert 352]

Stu, it is I who is suffering the embarrassment for as Jeroen and Jonners say it is unlikely to be a valve collet.

However I expect that we will know in a day or so what it is for there are two "bits" of metal still embedded in the cylinder head but I shall leave them there for Rod, my cylinder head man to remove.

I have not had the time today to peer through the back carburettor to see what might be missing from the carburettor itself. However the engine has a standard air cleaner assembly fitted and has had a (what was a new) filter fitted also so I would be surprised if it has ingested something from outside.

We will have a better idea though when Rod strips the head. Under normal circumstances I would have stripped the head myself by now but since Rod assembled it after skimming the head and fitting a number of thread inserts I think it is fair to let him strip it and then let him report.

I reported that it "looks" like bits of a collet in the head but I too had wondered how on earth a collet, or part would escape from under the bucket. There are two bits in the head and I am also tempted to remove the exhaust pipe and see if anything passed out through the exhaust valves and is sitting somewhere between the front manifold and the loop up over the back axle.

We will get this little blighter running again - and it will be "as good as gold" - as they say down here.

Stay tuned

Robert

[Dolly-Nut]

Peer down the carb throats with a touch and see if one of the screws that retain the butterflys is missing.

[soe8m]

A collet can only enter through the breather outlet pipe into the carb so mission impossible. It also has to go through the filter matrix in the valvecover before it can through the pipe. Then it can go far and away into the engine.

Jeroen

[Jon Tilson]

My money is also on a butterfly screw, extremely unlikely though that is, with the standard air filter what else could it be?

Jonners

[Dolly-Nut]

Needle securing screw possibly, or the collect it sits in although I don't think it's metal.

[Robert 352]

I have had a good look down through the carburettor and this is what you can see.

20130514-4110Pw Rear carburettor.jpg (128.75 KiB) Viewed 4243 times

Both screws where I expected them to be, nothing seems to be missing and since it has affected both #3 and #4 cylinders it is likely to be something that has passed down the manifold itself. Something that is/was in two parts for one part has gone one way and the other the other way.

Odd (and very frustrating) to say the very least.

(Takes a bit to hold that butterfly open against the springs and have a steady enough hand to get it into focus!!)

[Jon Tilson]

Needle securing bits then?

Jonners

[Dolly-Nut]

Or, if it has them, possibly a poppet valve (round thing on the butterfly at the bottom).

[Robert 352]

Another question for the experts!

I removed the #3 piston in order to examine the possible damage to the piston top where it whatever the foreign body (bodies) has been touching it and found some other somewhat disquieting evidence that all is not right.

If you have a close look at this photo which shows the side of the piston

20130520-4113Ptw #3 Sprint piston.jpg (117.49 KiB) Viewed 4190 times

you will see evidence of it rubbing on the side of the bore. The rubbing is immediately above the conrod.

Well that is what it looked like initially but further examination of the bore itself showed quite a nasty little burr just above the red arrow head here.

20130520-4117Ptw #3 Sprint bore.jpg (145.76 KiB) Viewed 4190 times

The question has to be what has caused this? It has obviously occurred after the block was bored and honed. Is it linked to the problem which has caused me to take the head off or is this just yet another problem which I have to resolve?

A final question, do you all fit new conrod nuts every time you take a conrod apart? I am unlikely to find conrod nuts here in this country and if I have to bring in a set, it is another delay of at least two weeks.

Robert

[Dolly-Nut]

I've noticed those marks on a few Slant pistons but obviously they shouldn't be there. However it's probably nothing to worry about. Also the marks in the bore are below the ring area, so it doesn't matter what it looks like.
As for the rod bolts, it's up to you. Some change them, some don't. But whatever you, loctite them.

[Jon Tilson]

There isn't a bit of ring missing is there? Sure you would have seen that.

I re-use rod and main cap bolts on Triumph engines all the time with no issues. You just need to use a torque wrench to do them up in stages...

Jonners

[Robert 352]

Gentlemen

All bets are off. I wish though I had taken your money.

My guess that it was a valve collet was close to what has happened. It was a valve spring which has broken and small bits of that spring have gone back up the #4 passage of the inlet manifold and down into the #3 cylinder.

One inlet valve – very bent, will join the shelf of bent and broken bits in honour of the God of Demon Speed. (Those of you who have seen the film “The World’s Fastest Indian” will know what I am talking about. The New Zealand Motorcycle GP used to be held at the Cust circuit just up the road from here. Bert Munro who built that Indian motorcyle will, I hope, be smiling down on me from somewhere)!

I will need along with one new inlet valve, which arrived in the mail from the UK today one new exhaust valve which I shall order from the UK this evening. I will need to replace a valve spring, a cam follower/bucket, a pair of split collets and the two collars which sit on the ends of the spring. Fortunately I have spares of all those here. There will be a further delay but there is little else I can do but to keep calm I suppose and carry on!

Robert

[soe8m]

How does it get from under the rocker cover into an inlet port??????

The only connection is the breatherpipe.

Jeroen