Honda XR cylinder head on a Dominator Engine?

[enduroman]

I'm the "happy" owner of a 1996 Honda Dominator engine, wich I plan to use in a Honda XR frame. The problem is that the cylinder head of this engine is beyond rescue, but the XR 600 engine is complete with lots of new parts. Still, I want to use the Dominator engine because of the electric starter and the 650cm3 cylinder. Do you know if the cylinder head of the XR fits the Dominator cylinder? In that case, I could just change the camshaft drive and chain to make it work, i guess?

[beat]

here you see a xl600r cylinder and piston mounted on a xr600r crank

this does not fit
because the stroke of the xr is longer than the xl.

if a xr600 head fits on a nx650, i don't know.
but i think it does if the xr is al 1991 or younger model

there are 2 different xr600 engines
1 with a manual decompresion and
1 with a automatic decompresion cam on the camshaft

a nx650/xr650l does have a cylinderhead with an automatic decompresioncam on the camshaft

however it will increase the compresion ratio do to smaller combustion chamber, so you dont need a high compresion piston

so that's my 2 cents

[Rubberchicken]

this does not fit
because the stroke of the xr is longer than the xl.

Hey, I didn't know that...

According to bikez.com:
XL600R (1985): bore x stroke = 100.0 x 75.0 mm
XR600R (1991): bore x stroke = 97.0 x 80.0 mm
NX650: bore x stroke = 100.0 x 82.0 mm

I know someone who has an XL600R with an older type XR head (with twin carb), so at least that fits...

The dommie has the same bore as the XL, so unless the bore of the XR changed when they changed to single carb, apparently it'll fit.

Does the bore continue on into the head? If it's flat it probably doesn't matter anyway, it's only 3 mm...

Oh, and you might want to keep the XR cam, she says the XL has a bit more punch up top with the XR cam... Though this may be a different cam on the earlier models, I don't know about that. Something you might want to experiment with anyway, power's always nice.

Do keep us posted, anyway.

[enduroman]

Thanks for your advice, guys! I guess the cylinder head of the xr600 will fit then, as the bolts/holes of the two engine heads seem to be identical. I'm gonna use both the crank and cylinder of the nx650, and the bore does not seem to continue in to the head, so by using a nx650 head gasket, this will hold, I guess. As far as I know, all the xr600 engines from 1985 on have the same bore and stroke, and the same compression ratio (9,0:1). The Dominator has a compression ratio of 8,2:1 if I'm right. A high compression piston will probably be good, but should I be replacing the bearings of the rod and crank as well? I've heard they should be replaced when replacing the piston? The xr600 cylinder of mine has manual decompression. Anyway it seems possible to replace the parts on the xr camshaft with the parts of the nx camshaft. In that case, I should be able to get autaomatic decompression, but will it matter? Thanks for all help so far!

[Rubberchicken]

I've heard of people specifically removing the auto decompression stuff from the NX cam, it can apparently cause some minor nasties at idle, but I'm not sure what...

If you have a healthy battery the starter should be able to crank it no problem, and the manual decompression is nice if you have a kickstarter on the bike.

Re: bearings. I'd say now that you've got her open replace as much as makes sense price wise, now's the chance... You wouldn't want the big end to go just as you've run in your newly rebuilt engine.

[enduroman]

Hi, again! I thought it through last night, and I totally agree with you on replacing the bearings. I have no idea what the cost would be, but it would be stupid not to do it now. The mechanic at our local Honda dealer is pretty good with the big singles, so I might get some advice there as well when it comes to the decompression parts. I'm always greatful for any further helpful information, and I'll keep you updatet about the progress!

[shuriken]

Enduroman, what was the out come? Looking at doing the same thing!

[enduroman]

Enduroman, what was the out come? Looking at doing the same thing!

Hello! I`m well into my second year working on this project, and it finally seems like it`s going to come together! I can`t confirm success yet, but it should not be a big problem making this work. I used a 1986 XR head on a 1995 Dommie engine, and it fits right on. Please mark that you have to use the cylinder head bolts from the Dominator engine to tighten the cylinder head, as the bolts have slightly different dimensions. The XR bolts will seem to fit at first, but you will not be able to tighten them properly. Still, the bolt washers from the Dominator will probably not fit, as the diameter will be too large fit into the washer seats in the XR cylinder head. Therefore you will probably have to grind the XR washer`s holes until you can get the Dommie bolts to go through. You can use either the camchain for from the XR or the Dommie, but I would recommend you to use the Dominator camchain, as it fits right on. I used the chain from the XR engine, because that one was new, but it`s slightly wider, so the chain guide from the XR will be very tight in the chain canal( or whatevere it`s called!). I grinded the guide canal on the Dominator cylinder a little bit, to get a proper fit, and of course I used the chain sprockets from the XR. The sprockets should fit right on to the crankshaft, as the splines are identical. the reason Ì haven`t tested the engine yet, is because I needed help from an electician to get the new wiring correctly. Most of the electrical system needs replacing, and I`m far form an electrician myself. The system is almost complete, but we have no spark yet, so we need to check the CDI-unit, pulse generator and go through the wiring diagram to see if we have missed something. I put in a high compression ratio piston, and as the combustion chamber of the XR600 is a little smaller than on the Dommie, I should have a compression ratio somwhere between 10,5:1 and 11:1. I`m really not sure if the starter motor will be able to crank the engine with that kind of compression, but I have manual decompression on the XR cylinder head, so I hope that will help. I hope to get it fired up this week. there are still a few challenges, though. On the old engine, I had dual carburators, but I want to use the single carburator from the Dominator. There are sligthtly different intake ports on the XR and the Dommie cylinder heads, therefore, I have to modify the intake a little bit, I guess. By the way, the single carburator is a Delorto PHM 41mm, and I have no idea how to get a throttle cable wich will fit, as the local dealer thinks the Dominator only came with MIKUNI originally. Do you have any suggestions? Anyway, I can only wish you luck on the project, I`m pretty sure you will succeed, and ìt shouldn`t be a huge job at all!

[enduroman]

Enduroman, what was the out come? Looking at doing the same thing!

Hello! I`m well into my second year working on this project, and it finally seems like it`s going to come together! I can`t confirm success yet, but it should not be a big problem making this work. I used a 1986 XR head on a 1995 Dommie engine, and it fits right on. Please mark that you have to use the cylinder head bolts from the Dominator engine to tighten the cylinder head, as the bolts have slightly different dimensions. The XR bolts will seem to fit at first, but you will not be able to tighten them properly. Still, the bolt washers from the Dominator will probably not fit, as the diameter will be too large fit into the washer seats in the XR cylinder head. Therefore you will probably have to grind the XR washer`s holes until you can get the Dommie bolts to go through. You can use either the camchain for from the XR or the Dommie, but I would recommend you to use the Dominator camchain, as it fits right on. I used the chain from the XR engine, because that one was new, but it`s slightly wider, so the chain guide from the XR will be very tight in the chain canal( or whatevere it`s called!). I grinded the guide canal on the Dominator cylinder a little bit, to get a proper fit, and of course I used the chain sprockets from the XR. The sprockets should fit right on to the crankshaft, as the splines are identical. the reason Ì haven`t tested the engine yet, is because I needed help from an electician to get the new wiring correctly. Most of the electrical system needs replacing, and I`m far form an electrician myself. The system is almost complete, but we have no spark yet, so we need to check the CDI-unit, pulse generator and go through the wiring diagram to see if we have missed something. I put in a high compression ratio piston, and as the combustion chamber of the XR600 is a little smaller than on the Dommie, I should have a compression ratio somwhere between 10,5:1 and 11:1. I`m really not sure if the starter motor will be able to crank the engine with that kind of compression, but I have manual decompression on the XR cylinder head, so I hope that will help. I hope to get it fired up this week. there are still a few challenges, though. On the old engine, I had dual carburators, but I want to use the single carburator from the Dominator. There are sligthtly different intake ports on the XR and the Dommie cylinder heads, therefore, I have to modify the intake a little bit, I guess. By the way, the single carburator is a Delorto PHM 41mm, and I have no idea how to get a throttle cable wich will fit, as the local dealer thinks the Dominator only came with MIKUNI originally. Do you have any suggestions? Anyway, I can only wish you luck on the project, I`m pretty sure you will succeed, and ìt shouldn`t be a huge job at all!

[shuriken]

Thank you for that write up. Where and how much was your piston? Is it a Wiseco one?