Anyone still ride a dommie?

**nx650** · #1 29 Dec 2005

Over here in NZ after riding from UK a few years ago and have bashed and bumped about 75 000 km out of my dommie still runs great but drags about a litre of oil down the valve guides every 1500km or so. Planning a trip round south america (which may well be another 40-50K) should I rebuild the old girl or are they a bit behind these new xr xrl types things these days any views?

**RichLees** · #2 29 Dec 2005

Dommie v XR is down to how you ride off-road. I did some trail bashing on a domie in the USA and it was more competent than me, but less competent than an XR: dommies are great on "light" trails and if I'd got as far as you have, I'd want to finish it off - the trip NOT the dommie.

are you sure that litre/1500km is only going via the valve guides? it sounds a lot! did you look at the back of the valve stem via the inlet and exhaust ports? with that much oil going that way, they'll be sopping wet. otherwise it might be the bore (either oil getting past the rings or air passing the rings and pushing oil up the blasted breather).

fix it or leave it? hmmm. that might depend on your view of the environment and blue haze ;-) I guess it might also make for interesting combustion on the high passes in South America if you're losing combustion pressure or efficiency.

personally, I'd check the valve stems and spark plug, then get a compression check before deciding whether to rebuild the top end. I think the top end gasket kit is 70-80 quid and piston, rings and rebore about 150.
PS I tried pattern gaskets and won't ever do so again - they stick to everything and are bastards to separate. eg clutch cover glued to crankcase ... never again :-(

**nx650** · #3 29 Dec 2005

It only blows the blue wonder on over run ie throttle off down a hill engine braking going into corners etc You sound like you know a bit if I have the motor out and apart is there any modification you can do to stop the valve seats dropping out. I have heard this to be a common and very damaging problem on these motors as they get older?!? Also your right I should carry on on the old bike I just still want to be able to trust it in the middle of nowhere

**JonStobbs** · #4 30 Dec 2005

Richard.
The problem with valve seats dropping out that you've heard of is down to cracks between the exhaust valve seats and the centeral sparkplug hole,in turn caused by overheating.This effects only the 600/650cc RFVC engine and is not normally economically repairable(as in welding repairs).Usually if you don't have a problem currently,and are contious of not letting the bike idle at traffic lights,etc...for more than 30 secs or so,then the cracks should'nt appear.If you're going to have the top end off to do the valve seals(and at least check the rings/bore while you're there),it won't be a chore to inspect the head for the aforementioned cracks.Clean off all the carbon build-up in the combustion chamber,and have a real good look between the valve seats and the plug hole.If there's no crack lines visible,you should be ok.
I second the opinion about not using pattern gaskets though for a different reason(headgaskets are very rarely the right thickness).One little tip if you can't get genuine Honda items and want to avoid the problem RichLees mentioned is to give the gasket a little coat of grease on both sides before assembly.Obviously this does'nt apply to head gaskets,but clutch cover,camcover,generator cover,etc...Quite safe as any grease squished out on tightening will just be disolved in the engine oil.

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Just going for a short ride on my bike....

**nx650** · #5 30 Dec 2005

Thanks mate I'll do that hey you wouldn't know if a lack of back pressure in non standard slip on exhaust systems can cause premature wear on the valves etc..? Someone mentioned it, my old system rotted out about 10 000km ago and I got one made up but it's much more free flowing great power increase but don't want to knacker the engine unless of course I already have. A free flowing exhaust should help the cooling though huh? wow a few questions there

**RichLees** · #6 30 Dec 2005

blue on the over-run does, indeed, sound like valve seals though its still worth checking via the inlet and exhaust ports before pulling it apart. as far as I know, Jon's right about the cause of dropped valve seats though I've had to dawdle in traffic in very hot places without trouble. actually, I was melting, but the bike was fine.

as for "free-flow" pipes ... I wouldn't have thought it would lead to premature demise of valve seals, but I wonder what it'll do for power on those high passes.

**LordStig** · #7 5 Jan 2006

Unless you've been running rather lean with the free-er exhaust can. Did you check the mixture after you replaced it? Lean running can lead to the exhaust valves burning out. It can't be that bad in your case or you'd know already, but I wonder if it could have damaged the seal in some way?

Stig

**POB/London** · #8 6 Jan 2006

Valve seats on the RFVC are small, so they do not dissipate heat well. If the ally head gets too hot, if differentially expands more than the seats and they become loose, dropping out. Problem is that then the valve closes and either 1)slams the seat into the hole, damaging the ally of the head or 2)bends the valve stem. Most often, both happen. I have seen this on a very low mileage XRL head, in HOT weather. Overheating of the head is the culprit. It is very hard to avoid, and is basically a design fault of the Honda haed that you have to live with. Welding the head is only an option if you can't get another one to use, IME.

**RichLees** · #9 6 Jan 2006

didn't yours get seized because your Super-Adept Mechanic forgot to put oil in? (yours is not the only bike to suffer at S.A.M.'s hands) ie your head might have come loose cos of that, so to speak.

**POB/London** · #10 6 Jan 2006

After the initial engine problem I had in Spain, the bike had a top-end / crank inspection and rebuild (including new valves and rockers) from DL. The valve seat problem happened many miles and a few months after that, when the bike had plenty of good oil, and a large Jagg oil cooler. Design fault, I say. Although I do love that engine - XR6, Dommie and XRL are some of the finest bikes ever made.