Mach 1-noisy top end

[nalimugmug]

Hi again,

Many thanks to all who have given there advice regarding my issue.

I acquired this engine as a basket case way back in 2003, all the components had actually been bagged off into there individual whole items.

At this time in my life I was working, this work entailed that I was out of the country somewhere in the World for six weeks straight, this was followed by three weeks at home, taking into account jetlag in some home visits I couldn't really find the time or inclination, and to be perfectly honest with myself, getting the engine back to an item was outside my comfort zone.

A local one man motorcycle shop who specialised in tuning and racing his own two stroke bikes offered to take on the task for me. From him initially receiving the parts it was two years later that the task was finished, due to this protracted time he refused to accept any payment for the work.

Sad to say that during one of my out of country excursions this guys workshop burnt down and he and other factors in the building lost everything, thankfully nobody was hurt. This guy has since moved away from the area so I'm not able to speak to him about the build. Is it possible that due to working only on two stokes, he just bolted on the head ? who knows. As Nigel states, clearances should of been checked but obviously were not.

Anyway, so here I am faced with getting this sorted out. The witness mark in the piston pocket looks worse than what it is, I can barely feel it with a finger nail, and thanks to Nigel for his observation that the piston was hitting the head, with my concern being the marks in the pocket I didn't notice this. But now its been pointed out its rather difficult not to see it.

Today I've ordered a piston ring compressor and some modelling clay from the net, ill remove the piston and in doing so I will clean up the pocket damage using a Dremel, I could do this in situ but then there's swarf to be taken into account that may get to places where's its not welcome.

Looking in the Ducati parts book I can see that there are two base gaskets available, the one fitted at the moment is .5mm where a 1mm is available.

I'm waiting for some flat iron bar to arrive so I can fabricate the hair spring compression tool so I can check if the valve guides are worn.

viewtopic.php?f=3&t=1916 - bottom of page one- thanks Recluse for this

If I were to fit the thicker gasket, reassemble everything using the clay impression technique this would then let me know what to do from the results.

Of course I'm open to suggestions if any of this could be bettered.

If there was a pub open now I would be in it-

Thanks in advance

Bob

[LaceyDucati]

Hi Bob
Being the ever pessimist, I'd pop the cylinder off and just give the rod a check to make sure the bigend looks/feels okay. That could be another reason for the piston coming up too far. Assuming all okay you will likely need to add at least another 1mm under the cylinder to add around 0.6mm to the measured squish.

I measure the squish with 12 pieces of leaded solder (0.9mm) placed around the squish like a clock face and held in place with blobs of grease. Arrange the piston just short of TDC and then fit the head and torque it down, pop the engine over TDC and remove the head. You can then measure the solder, don't be surprised if it's not totally consistent, some are well out and poorly centralised reboring will make this worse. I would not run much less than 0.75mm (30 thou) on a 250/350 (45 degree) road bike especially if you are using base gaskets. This is because they are likely to compress further in use and is the reason I would only ever use base shims (compression plates) for racing.

Once you have the squish set, you can use the modeling clay in the pockets to check the valve to piston clearance. I roll a roughly 6mm "sausage" and lay it around the pocket edge, lightly pressing it into position. Always check the valves and ports after testing the clearance as it can sometimes end up in the port or under the seats. Best practice would be to carry out all these tests and then strip the head down and wash everything before final assembly. I like a 2mm min clearance on the inlet and a 2.5mm min clearance on the exhaust, with a 1mm radial clearance to the edge of the pocket. That's how I run my race engines and I know others run things tighter.....but it's what I do.

You may well find your pocket issue disappears when you set the piston height correctly, so don't start attacking things before you check measurements first. A good engineers saying "measure twice cut once!". Personally I would machine the pocket or get someone to do it.....I'll stop here

Regards Nigel

[nalimugmug]

Hi Nigel,

Thank you so much for your detailed approach to getting my issue sorted.

I've just removed the barrel and I'm relieved to say that there is absolutely no up/down movement with the con rod.

Looking on your website, I have noticed that you have aluminium base shims, what would you opt for to suit my application?

My progress now comes to a halt until my piston ring compressor arrives.

I'm sure all will agree who use this forum that you are a first rate engineer who has no qualms about sharing your vast experience with these machines.

Many thanks

Bob

[George]

Hi Nigel,

Thank you so much for your detailed approach to getting my issue sorted.

I've just removed the barrel and I'm relieved to say that there is absolutely no up/down movement with the con rod.

Looking on your website, I have noticed that you have aluminium base shims, what would you opt for to suit my application?

My progress now comes to a halt until my piston ring compressor arrives.

I'm sure all will agree who use this forum that you are a first rate engineer who has no qualms about sharing your vast experience with these machines.

Many thanks

Bob

I will second your comment. My first Ducati restoration and Nigel has been very helpful and gives practical advice. A man worth listening to.

[LaceyDucati]

Hi,

Thanks for your kind words guys

Bob,
Yes a base shim would be preferable to a load of gaskets. We have limited stock at the moment, but are awaiting a new batch we are having manufactured. Unfortunately the order is very late due to implications of the lockdown. As the piston is already touching my guess is you will need probably 1.2 to 1.5mm more than you have at the moment, that will give about 0.7 to 0.9mm more measured squish. Assuming you already have a 0.5mm gasket the correct height could be achieved either by adding a shim with sealant on one side or probably by using a 1mm shim sandwiched between two 0.5mm gaskets. 0.5mm gaskets will probably only compress 0.05 to 0.1mm maximum, so that seems like a likely good solution. I suspect your valve clashing issue will be significantly reduced with the addition of a further 1.5mm.

As to why you should need to raise the cylinder remains unknown. I would check your cylinder base as it may have been machined, original cylinder surfaces are crosshatched in finish. Failing that it could be a piston deck height issue, either way it should be recoverable.

Nigel

[double diamond]

Had the same issue on a 350 widecase although May have been exacerbated by valve float. Installed a new exhaust guide and increased the diameter of the valve pocket slightly. This addressed the contact issue but the valve was also slightly bent. You should inspect the valve and the valve seat for concentricity.

Matt

[nalimugmug]

Hi Matt,

I'm still waiting for the material to arrive so I can fabricate a hairspring compression tool.

When I do get the valves out I will check for damage to not only them but everything else.

Thanks

Bob

[LaceyDucati]

Good point Matt, my rule with valves is "if in doubt replace it". A relatively cheap item in an engine that can lead to untold destruction if it fails. Valves that have been hitting a piston repeatedly for many thousands of times a minute are best discarded.

Bob, I'll reply to your email tomorrow.

Nigel