Why place a Honda Hawk camshaft holder in XRV750 engine??

[Guest]

Hello Hawk friends,

I'm a Honda Africa Twin XRV750 Rider from the Netherlands and have a technical question what I think best can be answered by the Hond Hawk community

I bought a secondhand XRV750 engine to replace my current heavy oil using engine in my Africa Twin. I bought it from the shop "Offroadcentrum" in Epe in The Netherlands and was told it came from an unfinished project.

As I have discovered this project would probably be a Honda Hawk project since the valve covers were from a Hawk, There was a 17tooth sprocket mounted, the waterpump mount was modified and most of all there were added external oil lines from the bottom of the engine to the Cylinder heads. Inside the heads I noticed that the Camshaft holders were also that from a Hawk and not from an Africa Twin.The AT has an internal olie line which feeds the oil to the camshaft and valves through the Camshaft holder. I guess the external oil lines are added because the camshaft holders from a Hawk dont have these internal oil lines.

My main question is why would the previous owner used the Hawk camshaft holder and added the external oil lines instead of using the stock AT holder which includes the internal oil feeds?
Hopefully I can get some insights in this AT engine block so I can build it in my AT knowing what has been modified and/or possibly change it back to the stock AT setting before building it in and get my motorcycle back on the road!

[yorkshire]

I would say the cylinder heads are of the external oil feed type, maybe not the original heads, I have no experience with africa twin motors, what does the crankcase stamped number tell you?

[Guest]

Hi yorkshire, thank you for your reply. I am almost certain that the cylinder heads are from an AT engine. I have loosened the nut where the arm from the original AT camshaft holder would be mounted and there is definitely enough space for oil to be pressed up around the bolt.

Below is a picture of the Camshaft holder from an AT with "the arm" I'm talkin about at the bottom right from with oil lines inside.
XRV750 camshaft holder.PNG

[behindthetimes]

Maybe its all he had and he didn't care.That has as much cred as any other reason,How's it run?

[Yoshihns]

Going back to stock is always a safe option. I have no idea why things would be changed.

[DrPMC]

Are you sure that Hawk heads haven't been fitted? They are the same casting as the XRV750 heads and - I'm guessing - the only difference is the internal oil feed. Presumably the heads and the cam retainers are machined in one piece and its good sense to keep them together?

As Behind the Times suggests, maybe the previous owner needed replacement heads and the NT650 ones were the only ones available? Or perhaps they've got bigger inlet valves than stock and a gas flow job? Have you taken them off and had a look? Probably looking down the inlet tract will show?

[Guest]

I haven't run the engine jet and would like to know what I have before putting it in to my bike Not 100% sure it's a XRV750 head but found out that the castings are a little bit different, the 'arm' in the Camshaft Holder with oil line mounts on a flat part of the head that's not there on all Hawk heads, see picture below.

hawk vs Twin.png
I haven't run the engine jet and would like to know what I have before putting it into my bike Maybe the previous owner indeed didn't have other parts available and just made the engine run with the parts he had.. but adding an external oil line and drilling a hole and tapping in the thread doesn't seem like the work of someone who doesn't have time to get the correct parts..

Changing it back to stock seems to be the best solution. First I will block off the added external oil lines and check if there is coming oil up from the internal oil feeds.
Was hoping this modification with external oil lines was maby a well known trick within the Hawk community but this could be just an exceptional project engine.

[DrPMC]

I hadn’t noticed that difference between the AT and Hawk cylinder heads and stand corrected . It doesn’t seem to make much sense to add those external oil lines.

I have a broken AT engine that I bought for spares - when it went wrong it broke the crank and one of the cam retainers must have been starved of oil because it got so hot the aluminium distorted. No idea if that is a more common problem or a one off.

Looking at the pictures of your engine I noticed that the valve spring retainers have been lightened - I wonder what other modifications are inside?