What the ....!

[UKROBK7]

Just thought I'd share this with you. 
Changed the exhaust valve guides today on the K7.  New fan oven set to 170 deg C (thanks Marg).  Head well supported and soaked for at least 40 minutes at that temperature.  Used stepped drifts to get them out and to put them in, the stepped drift for putting them in went all the way inside the guide to support it.  Head put back in oven for each guide operation.  Really tight to get them out but not so bad putting them in.  All went well until this happened!  Change in note from the drift, pulled the drift out and the top of the guide fell off!

I have changed a number of guides on different engines and never a problem until now.

Rob

[UK Pete]

Was That the old guide that broke,  are you planning to recut the valve seats?
Pete

[Waggles]

Never seen that before! looks like a fault in the guide though doesn't it, It looks like it has become brittle somehow. If that was the new guide ( which I assume it is ) did you cool it before fitting? Have had some success in the past freezing the guides before fitting, could then almost push them in to the heated head by hand. Rather suspect even that technique would have caused this one to fail though, from thermal shock if nothing else!

[UKROBK7]

It was the new guide that I was fitting and it had been in the freezer as well as heating the head.  I think (hope!) it was a fault with the material.  Just ordered another one and see how that goes.

Pete, I am getting the seats cut as although I have got away with it in the past by blueing up the valve face and checking the seating but the seats on this head are out of spec and need narrowing up,  the inlet seats show chatter marks as well.

I had a quote from SEP (£25) but they are on a 4 week lead time so I have taken the head to a small automotive engineering company who specialises in motorsport this morning for him to see if he had the equipment to cut the 3 angle seats as he was concerned that he might not have a cutter and pilot the correct size.  Also Honda specify 37.5, 45 and 63.5 degrees for the angles and I think he said the "normal" cutters are 30, 45, 60.  he has taken delivery of a machine that cuts the 3 angles in 1 cut, the blades being supplied pre-ground.  He has one that has the required 45 degree and 1mm seat width, not sure about the lead in and out angles but the 45 angle is the important one.

Anyway, he says he can do the 8 for £3.50 a seat on a same day turn round BUT he has rejected the 3 used inlet valves I wanted to use.  I had bought 4 new exhaust valves and 1 new inlet valve and thought the other 3 inlets would lap in OK but he says not so I've just ordered replacements.  As you know you can't grind the valve faces and these were showing signs of recession where they hit the seat so he thinks they would ruin the nicely cut new seat when you try to lap them in.  When the parts come I will try him out and see what happens, at least he's reasonably local and i can keep on top of things. 

He has suggested he turns down the back face of the inlet valves on a 30 degree taper to improve flow, he does this for a lot of motorsport engines.  Anyone had this done on our engines?

One problem with his workshop - I have come out smelling of suds which takes me back a few years and you can't get rid of it out of your clothes!

Rob

[K2-K6]

I haven't any experience of modifying the valve angle on these but know the head seems possibly at odds with some more general practices used on other motors.

From my point of view and availability of components for these then I'd go with what is most reliable as the gain is potentially very small but it you get a failure it's all stuffed.

Any flow increase would probably need different carbs to capitalise on it to any great degree.

[UKROBK7]

My thoughts as well.  Unless I was going to build a performance engine I believe I should leave the parts as original, the thought of loosing a valve head after all the work I've put in terrifies me!

rob

[UKROBK7]

Update. 
The replacement guide went in OK, head (not mine but I felt like it) in the oven and guide in freezer.  Measured guide OD before fitting and it was 12.04mm.  I believe the head is reamed 12mm so there is 0.04mm interference fit (0.00157" in old money).  I cleaned the guide and hole before fitting and turned up a 'guide' for the guide to keep it square to the head, I still can't believe these are so tight to get in.

Replacement inlet valves arrived from D.S but were sent back as they had slight corrosion on the stems and seats (you have to watch NOS parts for storage and handling problems) which I felt would ruin the nice new guides and seats.  No problem, good service as always, they ordered in new Honda items as they are still available.  Looks like the seat cutting has been put back another week!

Rob