head advice and cost

fendermanz · Dec 18, 2023

Hi guys, I am a diy when possible. and this forum has been really great to help be in my journey to bring my 71 750 commando back to life. I'm pulling the head off and got a quote from a local machine shop in Canada for $480.00 ($283 pounds for the uk) plus taxes and parts and using k/b valve guides bronze only. Is this reasonable? I was also contemplating doing the heating/freeze diy method as mentioned in the forum. I used to work in a machine shop 30 years ago, still got my micrometer, calipers etc. I plan on just riding this bike on occasion, no racing etc. I have been trying to read the forums but lots of differing opinions.

I could also save that money and buy the tools needed. This is probably like another what oil you use type of thread, I apologize.

grandpaul · Dec 18, 2023

It all comes down to your personal budget and comfort level.

If heads ever needed anything beyond a good cleaning and valve lapping, I ALWAYS had the machinist refurbish them. I COULD do it myself, but my time was more valuable proceeding with the rest of the restoration/rebuild, and letting the pro do it.

htown16 · Dec 18, 2023

If you are replacing the guides, the seats need to be recut to be concentric. Probably best left to the pros with their much superior equipment to do that job. So since the head is already in their hands might as well have them do the guides. Make sure they ream the new guides to proper clearance on the valve stems as they tend to close up a bit during installation. A light, emphasis on light, skim cut on the head to true it up is also a good idea. If your 400$ quote includes all this, it's a bargain.

baz · Dec 18, 2023

fendermanz said:
Hi guys, I am a diy when possible. and this forum has been really great to help be in my journey to bring my 71 750 commando back to life. I'm pulling the head off and got a quote from a local machine shop in Canada for $480.00 ($283 pounds for the uk) plus taxes and parts and using k/b valve guides bronze only. Is this reasonable? I was also contemplating doing the heating/freeze diy method as mentioned in the forum. I used to work in a machine shop 30 years ago, still got my micrometer, calipers etc. I plan on just riding this bike on occasion, no racing etc. I have been trying to read the forums but lots of differing opinions.

I could also save that money and buy the tools needed. This is probably like another what oil you use type of thread, I apologize.

What is actually wrong with your cylinder head?

Stephen Hill · Dec 18, 2023

Last summer I had the same considerations as fendermanz. I wanted to do as much as I could (and I have lots of skills and tools etc). What made the most sense for me was:
-I dismantled the head and cleaned it up.
-I removed the guides and installed them myself. (Note: don't order your guides until you know what OD size you need).
-I purchased the guides and valves I wanted through my suppliers.
-I found a shop with a decent reputation and reasonable turnaround times and gave them a printed page of instructions, clearances, etc.
-The shop reamed the new guides and dressed the seats. My machine shop price was about half of your quote.
-I had the head vapour blasted (different shop).
-I rubbed the head flat on a surface plate, countersunk the edges of the threaded holes, and assembled the head.

Unless you are doing a lot of head work, IMHO it probably isn't worthwhile buying reamers and seat cutters.

seattle##gs · Dec 18, 2023

I just hand the head over to a shop that cares about motorcycle stuff. The local shop charges about $650 to supply valves, guides, springs, and labor. This includes helicoiling the three studs.

marshg246 · Dec 18, 2023

How did you determine that the guides are bad and if you didn't why are you changing them? Same question for the valves. In the US at least, many bikes are quite low mileage and often don't need guides and/or valves. Sometimes if a bike has sat a long time the one open valve will be pitted and the rest will be good.

If the valves and guides have nothing wrong with them, IMHO, it's a waste of money to change them.

I always leak-check, disassemble, fully clean, check the springs, check the valves in the guides and if OK, lap them to be sure there is an even pattern all the way around. If heated well, drifting guides out and in is no problem. If an oversize is needed, then I would get another head (can't find a good machine shop). I've found collapsed springs more often than bad guides.

Schwany · Dec 18, 2023

seattle##gs said:
I just hand the head over to a shop that cares about motorcycle stuff. The local shop charges about $650 to supply valves, guides, springs, and labor. This includes helicoiling the three studs.

Are you talking about Autosport in NW Seattle? Oddly John told me he didn't want to work on Norton engines again after he bored a set of iron barrels for me. Maybe he changed his mind.

Deckard · Dec 18, 2023

A '71 head is a good vintage, it wasn't ported like later Combat or 850 heads and flows quite nicely. Your price for work is reasonable. That year head needed valve guides and seals to correct deficiencies in manufacturing. I had to do that, probably everyone else did who bought a 750 in that era.
After that, all good.

worntorn · Dec 18, 2023

Re 850 heads and port shape-
There are 3 different heads for the 850. According to DynoDave of Atlantic Green, the 32 mm port shape on the common rh4 (73 & MK3 850) is much better than the 32mm Combat.
From that site-
"The combat RH3 was cut .042" to raise the compression. It had a 32 mm porting job. It appears the factory learned more about the porting business as time went on. First hand inspection of several "combat" porting jobs show how crudely (bad) they were done. Big.... yes. By today's standards these heads have been ruined. The "BIRCO" on the right and the casting number faintly visible on the left side are negatives (depressions in the surface)."

The 30 mm RH 10 (74 850) seems to be better yet, or a least it has enough material still in place to give the hotrodders something to work with.
I haven't found much info on the high compression 32 mm RH9. It might just be a shaved RH4.

Glen

Torontonian · Dec 18, 2023

fendermanz said:
Hi guys, I am a diy when possible. and this forum has been really great to help be in my journey to bring my 71 750 commando back to life. I'm pulling the head off and got a quote from a local machine shop in Canada for $480.00 ($283 pounds for the uk) plus taxes and parts and using k/b valve guides bronze only. Is this reasonable? I was also contemplating doing the heating/freeze diy method as mentioned in the forum. I used to work in a machine shop 30 years ago, still got my micrometer, calipers etc. I plan on just riding this bike on occasion, no racing etc. I have been trying to read the forums but lots of differing opinions.

I could also save that money and buy the tools needed. This is probably like another what oil you use type of thread, I apologize.

What's the mileage on your machine ? Many could not be kept running long enough to wear out . I watched Gord slip the free valves back into their respective guides , do a little wiggle to each and then ask me to get him new ex. guides . I'm sold on new intake seals every time the head is off . Not Norton crummy plastic that goes hard , splits , or even come off and ride up and down the stems . J.S. Motorsports sell really great teflon ones with spring retainers . My bike does not smoke , just like me . Your decision and money .

htown16 · Dec 18, 2023

The 30mm rh10 head used a tapered maniford to run the 32mm carb. I had a pair in my spare parts collection and measured them. Got to wonder why they didn't do that for the combat instead of hogging the head out.

acotrel · Dec 18, 2023

Over-porting the cylinder head is probably the first mistake many people make. As far as valve guides are concerned, if you take the springs off, you can feel if there is too much slop in the guides. I would always fit new springs. I used to have the valves sychro-seated. But these days I would find somebody who has the three different angle seat cutters and hand-lap the valves. The one which cuts the outer angle can improve performance.

fendermanz · Jan 1, 2024

htown16 said:
If you are replacing the guides, the seats need to be recut to be concentric. Probably best left to the pros with their much superior equipment to do that job. So since the head is already in their hands might as well have them do the guides. Make sure they ream the new guides to proper clearance on the valve stems as they tend to close up a bit during installation. A light, emphasis on light, skim cut on the head to true it up is also a good idea. If your 400$ quote includes all this, it's a bargain.

that's 400 then whatever parts I need.

CanukNortonNut · Jan 2, 2024

Where are you located fendermanz. If you are in Ontario I could point you to some Machinists that do Norton heads. I'd recommend Kibble/White valve guides and Black Diamond valves plus new springs. As stated above if you replace guides they need to be reamed to size and valve seats re-cut.
Cheers,
Tom

fendermanz · Jan 4, 2024

CanukNortonNut said:
Where are you located fendermanz. If you are in Ontario I could point you to some Machinists that do Norton heads. I'd recommend Kibble/White valve guides and Black Diamond valves plus new springs. As stated above if you replace guides they need to be reamed to size and valve seats re-cut.
Cheers,
Tom

I'm in Niagara. One racing machinist said he only does bronze k/w guides. I was reading here that cast iron is good for regular riding.

CanukNortonNut · Jan 4, 2024

I use the kibble white guides and black diamond valves for my street bike and they are great. I have put a lot of miles on it with these bronze guides. I would recommend them over Cast iron guides. Cast Iron guides sometimes break apart. You can get these K/W guides and valves at British Cycle Supply or Walridge Motors. Inlet valve guide seals; I would recommend the K/W seals but they are a Harley number 71006-4 I think???(somebody help me here), or the J.S. Motorsport type that he sells here: https://jsmotorsport.com/product/viton-valve-guides-seals/
I'm in the Smithville / Hamilton area.
Don Morris from Mount Hope and Carl Simmons out of Caledonia both have done head work for me. Don is more expensive. He also doses H/D's and dyno work. Carl is a CVMG member Cayuga Chapter.
PM me if you want their number.
Cheers,
Tom
P.S. become a Ontario Norton Owner member and join the club https://ontarionortonowners.com/ We will be holding a Norton Rally for the ONO's in June at Barry's Bay this year. Should be a Great Ride event.

Blewdy Yaink · Jan 5, 2024

htown16 said:
(snip) A light, emphasis on light, skim cut on the head to true it up is also a good idea. If your 400$ quote includes all this, it's a bargain.

Good advice on valve guide installation and valve seat recutting. Regarding the skim cut on the head, I've found that many Commando heads have the head gasket face and the area for the head steady (Isolastic) to be out of true - usually there is about a 8-thou runout across the head steady surface. When I'm re-skimming a head gasket surface, I prefer to remove the cylinder studs, have the machinist bolt the head down on the mill table on it's head gasket face and re-cut the head steady area. Then, flip it over and skim cut the gasket face to be parallel to the newly true head steady face. A little more time and $$$ but you can be sure that the working parts (valve train, etc.) in the head are properly aligned.
This makes it easier to keep the material removed by the skim cut light (emphasis on the light) and true.

head advice and cost

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