Author Topic: CB750F1 Valve guide reaming  (Read 391 times)

Offline martin_uk

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CB750F1 Valve guide reaming
« on: November 19, 2018, 10:19:46 AM »
Just spoken to guy that usually does my machining and has fitted a new guide for me.

Only one was needed and bought a genuine Honda one from DS

He says that a non standard reamer is required and he does not have one :-(

Anyone have one to loan or recommend where to get?

Just off to collect.

I am making progress on my final? CB750, but slower progress than first ones.

Frame and wheels just about there, assembled lower engine.

Cylinders rebored and ready to paint, now need to finish top end and make up a set of carbs from all the bits ::)

Thanks
1977 CB750F1
1978 CB750K8

Triumph Street Triple 675R
Triumph 3TA
AJS 350 mod16

Offline martin_uk

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Re: CB750F1 Valve guide reaming
« Reply #1 on: November 19, 2018, 08:43:05 PM »
I have checked and appears to be a 6.6mm reamer required.

Found one in Germany on Ebay,  so will see how it works out.
1977 CB750F1
1978 CB750K8

Triumph Street Triple 675R
Triumph 3TA
AJS 350 mod16

Offline Trigger

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Re: CB750F1 Valve guide reaming
« Reply #2 on: November 19, 2018, 09:03:15 PM »
It depends on how much your valve stems are worn or if you are using new valves and what the stem size is  ;)
I ream the valve guides to the stem size and then use a expanding ream to ream to spec.

Offline Yoshi823

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Re: CB750F1 Valve guide reaming
« Reply #3 on: November 20, 2018, 10:02:34 AM »
When I machined 8 new valve guides out of ally-bronze I reamed them to size (6.6mm) after they'd been inserted into the head. I bought this special size from a local engineering firm for not a lot (I think that it was about £10 but it was a long time ago).

I then had the valve seats recut to accept new valves.
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Offline Trigger

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Re: CB750F1 Valve guide reaming
« Reply #4 on: November 20, 2018, 06:46:34 PM »
Putting new valve guides in will always require the valve seats to be re ground as, it it near impossible to ream true to a seat  ;)

Offline martin_uk

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Re: CB750F1 Valve guide reaming
« Reply #5 on: November 21, 2018, 09:09:26 PM »
Assume normally ream from combustion side?
1977 CB750F1
1978 CB750K8

Triumph Street Triple 675R
Triumph 3TA
AJS 350 mod16

Offline martin_uk

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Re: CB750F1 Valve guide reaming
« Reply #6 on: December 01, 2018, 09:52:52 PM »
The reamer has arrived and is a close fit on the non replaced guides, but does not have a lead in.

Without a lead in, concerned that it will be difficult to correctly align.

The finished size needs to be 6.6mm. I have seen Chinese adjustable reamers, but not sure about quality and will take quite a few weeks to arrive

As an alternative, has anyone had guides reamed and can recommend a company in the South?
1977 CB750F1
1978 CB750K8

Triumph Street Triple 675R
Triumph 3TA
AJS 350 mod16

Offline Laverda120

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Re: CB750F1 Valve guide reaming
« Reply #7 on: December 02, 2018, 07:38:48 PM »
You could try J D Autoworx based in Wallington.

Offline Bryanj

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Re: CB750F1 Valve guide reaming
« Reply #8 on: December 02, 2018, 10:23:48 PM »
If there is no lead on the reamer sounds like a machine one instead on a hand one

Offline martin_uk

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Re: CB750F1 Valve guide reaming
« Reply #9 on: December 04, 2018, 08:28:13 PM »
You could try J D Autoworx based in Wallington.
Thanks I will give them a call
1977 CB750F1
1978 CB750K8

Triumph Street Triple 675R
Triumph 3TA
AJS 350 mod16

Offline martin_uk

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Re: CB750F1 Valve guide reaming
« Reply #10 on: December 04, 2018, 08:30:54 PM »
If there is no lead on the reamer sounds like a machine one instead on a hand one

Yes it was described as machine. Does that mean it has to be set up precisely rather than using a variable speed  hand drill?
1977 CB750F1
1978 CB750K8

Triumph Street Triple 675R
Triumph 3TA
AJS 350 mod16

Offline K2-K6

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Re: CB750F1 Valve guide reaming
« Reply #11 on: December 04, 2018, 08:58:13 PM »
Machine reamers have a "plug" form, in that they are parallel flutes all the way to the end and making them difficult to get them into the work material to start them cutting.

Usually they are for use on things like a milling machine or jig borer that presents the tool straight into the drilled hole with no misalignment.

Hand reamers have a taper on the lead end of the tool that allows the reamer to enter the valve guides (effectively being under sized)  before the cutting flutes reach correct dimensions.  Normally you can use them with a tap wrench to hand ream the hole as they only need to go slowly.

Offline Bryanj

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Re: CB750F1 Valve guide reaming
« Reply #12 on: December 04, 2018, 09:35:18 PM »
You must not use a machine reamer in a hand drill as the chances of breaking both it and the valve guide are extremely high. Sorry but you have wasted the money on  it.

Offline martin_uk

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Re: CB750F1 Valve guide reaming
« Reply #13 on: December 09, 2018, 04:07:32 PM »
Life is a continual learning experience and I have wasted far more money  :P

I spoke to engineering co suggested in Wallington and they can diamond hone for about £30, but it means getting it to and from them.

I have bought an adjustable reamer from UK so will see how that goes.
1977 CB750F1
1978 CB750K8

Triumph Street Triple 675R
Triumph 3TA
AJS 350 mod16

Offline martin_uk

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Re: CB750F1 Valve guide reaming
« Reply #14 on: December 09, 2018, 04:08:48 PM »
You could try J D Autoworx based in Wallington.
Thanks for suggestion
1977 CB750F1
1978 CB750K8

Triumph Street Triple 675R
Triumph 3TA
AJS 350 mod16