Dommie engine trouble & cam chain tensoner special tool!?
 

Hi,
Rebuilding my Dommie engine and could really do with the cam chain special tool. This tool holds the cam chain tensioner back when replacing the cam chain. Anyone got one I can borrow/buy?

Also, reason I am rebuilding the engine is that last year, going up a hill, the engine suddenly gave way with a large amount of smoke!!! Removed the head and valves etc are ok and piston looks ok but slightly wobbles inside the cylinder. I would say that the rings have gone. Anyone else had experience of this?
Cheers,
Dave

its a bit fiddly, but you can compress the spring with a wire around the tensioner, drop it into the tunnel and cut the wire. just don't drop the wire down into the engine!! alternatively, a nice fat screw driver to stop the end of the spring snagging and a second pair of hands.

don't know about the smoke. the piston will have a very small amount of play in the bore and I would think that a perceptible amount might be too much.

Why not remove the cam chain tensioner to ease fitting of the new cam chain?

Surely the Dommie tensioner has the usual sprung loaded ratchet type mechanism with a gasket beneath?

Cheers Rich and Steve,
Not sure it's the 'usual'. Must admit, although I have taken many car engines apart it's my firstbike engine and I haven't removed it before. Not sure how the thing comes off actually. In the picture in the manual (not great pics by the way), it seems you remove a bolt on the inside of the engine and then with pliers pull the cam chain tensioner out? Not sure though as I tried this and it seemed pretty tough to pull (didn't want to keep pulling in case something else needs to come off!!). How long do these chains last by the way as I have the engine apart anyway to replace the piston rings.
Cheers for your help guys!! MUCH appreciated!!!
Dave

Cam chain tensioner normally sits on the rear of the cylinder & to one side and is a sprung loaded ratchet. Once the tensioner guides/blades & cylinder head are in place, you check the valve timing is correct & bolt the cam chain tensioner on to the cylinder (2 x 6mm bolts?). It then tensions the chain. Re-check timing & carry on. They're quite simple bits of kit. On some bikes they're hydraulicall activated useing engine oil pressure & some are a mixture of spring & hydraulic pressure.

Cheers Steve,

Any idea how long the cam chain should last? The bike's done about 50k miles and been regulary serviced.

if you've removed the vertical bol from under the rocker cover, you can now pull the tensioner rod out and then take the tensioner spring and arm out upwards. the spring will pop open and that's what's fun to compress to reinstall behind the tensioner blade.

at 50k miles, I'd replace while you've got the chance! that's got to be close to service life. its also worth checking the tensioner blades/guides for excess wear.

where in London are you? I might be able to give you a hand putting the spring back in if you're nearby. I work in Baker Street and live in Streatham

I've done this job many times. I made a tool from a 50mm nail. Just bend it to a u shape approx 10-25-15.Push the tensioner back using a screwdriver, push the pointed end into the hole in the tensioner and allow the other end to rest against the cylinder head.I also tie a piece of wire around the tool and anchor it somewhere just in case, never had a problem though. It makes the job a breeze

Hi Rich.. would have been great to have you help as I live in Dulwich.. only problem is that I am rebuilding my bike in Norfolk http://www.horizonsunlimited.com/ubb/frown.gif Thanks for the offer though! Think I shal change that chain whilst I have the thing apart. The tensioner looks ok but I need to run some gauges over the engine checking tolerances to be sure.

T bolt: cheers for the tip about the tool. Yeah I shall give that a go.

Thanks guys http://www.horizonsunlimited.com/ubb/smile.gif Lets get this baby going again.. has done me well so far as it got me to Singapore from the UK and also 3000 miles around the UK last year.
Dave