RH4 or RH10 ?

wbmoore · Dec 10, 2012

I'm working on a MK III that needs a lot of head repair work. It has a RH4 on it. Would a RH10 better than RH4 ? This is not going to be a HotRod. Any thoughts ? Thanks.

Nortiboy · Dec 10, 2012

wbmoore said:
I'm working on a MK III that needs a lot of head repair work. It has a RH4 on it. Would a RH10 better than RH4 ? This is not going to be a HotRod. Any thoughts ? Thanks.

RH10 has more metal where required and better performance. All round better head.

comnoz · Dec 10, 2012

wbmoore said:
I'm working on a MK III that needs a lot of head repair work. It has a RH4 on it. Would a RH10 better than RH4 ? This is not going to be a HotRod. Any thoughts ? Thanks.

The RH10 is faster and more durable. Jim

dynodave · Dec 11, 2012

A survey I did several years ago showed that about 1/2 of the RH4 heads sampled have cracks at the intake guides in one or both ports
:cry:

SteveA · Dec 12, 2012

Does someone have a stock of RH10s then?

There were less of them then, seems like there is a lot less of them now!

I understand it is the head of choice in used heads.....but how realistic is is to go looking for one?

Even a good used RH10 will probably need some of the work you need to do to your RH4!

Both heads suffer exhaust thread stripping, both heads wear valve seats and guides...what you have may just be good enough...check for cracks as described...

cjandme · Dec 12, 2012

SteveA said:
Does someone have a stock of RH10s then?

There were less of them then, seems like there is a lot less of them now!

I understand it is the head of choice in used heads.....but how realistic is is to go looking for one?

Even a good used RH10 will probably need some of the work you need to do to your RH4!

Both heads suffer exhaust thread stripping, both heads wear valve seats and guides...what you have may just be good enough...check for cracks as described...

This is where Fullauto comes in

BillT · Dec 12, 2012

I don't remember where I got this, but its been in my 'Norton' folder for a few years:

comnoz · Dec 12, 2012

I have that same list in my file.

One thing I always wondered.

Does the RH9 exist? I have never seen one. Jim

drones76 · Dec 12, 2012

http://sterlingmotorworks.com/norton_head_identifiction

Similar list. Slightly different part number for the RH9.

dynodave · Dec 12, 2012

It's been posted here for over 12 years: http://atlanticgreen.com/nhth.htm
But I have to admit the guy's email that sent it to me got lost about 4 computers ago....

BillT said:
I don't remember where I got this, but its been in my 'Norton' folder for a few years:

Brooking 850 · Dec 12, 2012

RH4 Head , just recently I had my Bike #1 head off to change the head gasket and did a leak down test and a visual prior to reassembling it, no cracking apparent.
What symptoms would indicate if I had a hairline crack through and around the valve guide area?
Regards Mike

comnoz · Dec 12, 2012

Brooking 850 said:
RH4 Head , just recently I had my Bike #1 head off to change the head gasket and did a leak down test and a visual prior to reassembling it, no cracking apparent.
What symptoms would indicate if I had a hairline crack through and around the valve guide area?
Regards Mike

Smoking exhaust, same symptoms as a bad valve stem seal. Jim

Brooking 850 · Dec 12, 2012

Thanks Jim, looks like I am in the clear, Bike # 2 project has a RH10 which will eventually end up on Bike#1
Regards Mike

nortriubuell · Dec 13, 2012

Does anyone have a picture they can post ... of where the RH4 head "cracks" :? I've read alot about it, but never actually seen it :shock: Thanks in advance.

SteveA · Dec 13, 2012

cjandme said:
SteveA said:

Does someone have a stock of RH10s then?

There were less of them then, seems like there is a lot less of them now!

I understand it is the head of choice in used heads.....but how realistic is is to go looking for one?

Even a good used RH10 will probably need some of the work you need to do to your RH4!

Both heads suffer exhaust thread stripping, both heads wear valve seats and guides...what you have may just be good enough...check for cracks as described...

Click to expand...

This is where Fullauto comes in

Exactlly CJ, and all I am saying really is that after 40 years it maybe a much more realistic prospect to pay for the new and imporved item than searching for an RH10, bearing in mind that most vendors know this is a more desirable item and price accordingly, but you will still need to renovate it for use.

But if someone does have a stock of them, I have an RH4 to trade in

mike996 · Dec 13, 2012

Just out of curiosity - were those heads on the list normal production heads that came on the bikes from the factory at different times? IOW, was an RH10 head the standard 850 head? Sounds like everyone agrees that the RH10 is the best but it would seem that the RH4 would have been a better 850 performance choice, at least at the top end of the rev range. Or is it that the 850's lower rev range can't take advantage of the larger port?

BillT · Dec 13, 2012

The RH1 was the head used for 750s up to the Combat

Don't know what the stock Combat head was, but could have been RH2 or RH3

The RH4 was the stock 850 head for '73 and '75up

RH5 is the same as the RH1, except with 32mm ports. I think it was the '73 750 head and the replacement head for earlier 750s

RH6 is apparently the replacement Combat head with slightly lower compression

The RH7 was the head for the short-stroke 750

RH8 and RH9 were special

RH10 was the stock '74 850 head

I'm sure if there are inaccuracies here, they'll be pointed out.

comnoz · Dec 13, 2012

mike996 said:
Just out of curiosity - were those heads on the list normal production heads that came on the bikes from the factory at different times? IOW, was an RH10 head the standard 850 head? Sounds like everyone agrees that the RH10 is the best but it would seem that the RH4 would have been a better 850 performance choice, at least at the top end of the rev range. Or is it that the 850's lower rev range can't take advantage of the larger port?

Just because a head has larger ports does not mean it will flow more air when bolted to the engine. An engine does not act like a flow bench. [although that is what the flow bench manufactures would like you to believe] Jim

Dances with Shrapnel · Dec 13, 2012

bwolfie · Dec 13, 2012

I have a RH10 head that needs a little loving, seats, guides and a little chamber welding. I would be willing to trade for a 750 head if anyone is interested.

RH4 or RH10 ?

Similar threads