[Ago37]

Hi Guys, I am new to the forum and looking for some advice for my 748sps.

I recently bought the beast above and with a promise of an up to date service history with a lack of paperwork I started to ask myself some questions...

The bike has covered 13k but I know all too well that a poorly maintained Duke can lose its valve adjustment pretty quickly.

On checking the shims nearly ALL are out of spec and at that time decided to pull the cams.

On doing this (as I sadly expected) my bike is showing pitting on 4 rockers with another 10 showing wear. At this point I knew this was going to be a big one for the wallet.

I have been through the saga of;

1) Buy new..... No chance (Im not Richard Branson)

2) Get another engine and strip it..

3) Or replate the originals.

After much thought and the temptation to buy a 998 engine I have decided to get the old rockers rechromed.

I have found a great local source in the UK for Hard Chroming but they cannot offer the reprofiling.

My question is... how much re profiling would be needed as the shims will need to be changed anyway.

Unlike a Camshaft I would imagine that the (ground and re-chromed rocker) would not have an altered duration like a peak of camshaft lobe.

Any help or advice on this would be much welcomed.

Thanks in advance guys!!!:blind:

 

[1fast750ss]

Hi Ago, welcome and sorry about the issue. There's god news though. Since the rockers are simply a platform for the valves, there's no bearing on how they affect measurement. Once you have them back in, then you will need to do a valve tolerance check. If you find some out of spec, find the ones that are loose and swap with the shims that are found to be tight in other valves.

Just be careful in knowing what part of the valve is tight, of course, whether it be the opener or closer.

Also, the best insurance on keeping a tight ship in your valve train is the use of MBP collets. The best $120 usd you will spend on that bike. They will lock in the valves so they won't loose their tolerance. I didn't have to do a valve adjustment for about 17k miles on my track bikes.

 

[tye1138]

Welcome to the forum!

Yea, the rocker flaking issue is very prevalent on the Desmoquattro engines. Its rare to find one without any rocker flaking. The replacement rockers from Megacycle (US cam company) Ducati Rocker arm Refinishing services and Crankshaft Balancing Specialists is probably the best option. The MBP collets will help as well, for sure worth looking into. You will need to re-shim with the new rockers because they're a different size then the old ones.

In terms of clearances, from my experience when the chrome flakes, you could have some clearance changes (too much clearance). If the chrome is eaten away, its not as tall and will for sure give you an alternative clearance. However, there isn't that much chrome on there in the first place, so would it put the valve way out of spec? No, not really. But if the valve is already almost out, then it will be further out for sure.

So as pointed out above, the rocker arms will need replacing and most likely the half rings (if you choose not to go with MBP collets). Your clearance issues may disappear if you replace the half rings as they are also a common failure point over the years of use. Sometimes it cheaper to just buy new half rings, install them, seat the closers and re-check clearances. Maybe your shims are fine?

 

[Ago37]

Many thanks guys!!! It's great to get some advice from people that know what they are talking about and have been through this before!!

The bike initially came apart due to me wanting to check the shim clearance, I measured this and all were way to small and she needed a total re shim, unfortunately then the rockers are goosed too.

The local engineer had commented he was happy to grind and then hard chrome them so hopefully that would do the trick. My only concern was when he mentioned he would not be able to re profile them..

Also if I have tight clearances and the rockers are re finished I will have absolutely zero shim clearance with my thicker rocker arms.

I guess I would have to use a. I micrometer to see how much thicker the rockers are when they are hard chromed again.

As for the mbp collets can you still get them? His site looks as if he has stopped making spares?

Many thanks again guys .

 

[tye1138]

So your clearances were tight? Can you give us some numbers?

The MBP collets are for sure still sold: MBP Ducati - Ducati Parts Online - Order Collets

 

[Ago37]

The intake opening shims 0.06,0.04,0.02,0.04. Unloaded
Exhaust opening 0.05,0.04,0.11,0.11 unloaded

Intake as above loaded 0.10,0.10,0.05,0.07 loaded
Exhaust as above loaded 0.12,0.12,0.12,0.12 loaded.

Any help guys is greatly appreciated.

I have also been looking at alternatives to hard chrome plating such as hardide or carbide coating.

 

[Ago37]

The intake opening shims 0.06,0.04,0.02,0.04. Unloaded
Exhaust opening 0.05,0.04,0.11,0.11 unloaded

Intake as above loaded 0.10,0.10,0.05,0.07 loaded
Exhaust as above loaded 0.12,0.12,0.12,0.12 loaded.

Any help guys is greatly appreciated.

I have also been looking at alternatives to hard chrome plating such as hardide or carbide coating.

 

[tye1138]

Those are in mm right?

If so, something is wrong… .06mm is pretty much no clearance. .006" is perfect.

Only thing I can think of is that you measured with the lobe in the wrong spot. I'd re-measure with the open lobe pointing straight up, forget about the whole TDC thing, the only thing that matters is how much clearance there is when the lobe is disengaged.

You can do DLC coating on the rockers, thats another idea.

 

[Ago37]

I'm sure I had checked them correctly I panicked as the clearances where practically nil. When looking in the SPS handbook they seemed miles away from the quoted ranges. From memory I think an intake unloaded was something like 0.11 to 0.24... Don't quote me on that.

 

[Ago37]

As for DLC I have been giving that some thought but just trying to get some prices on having that done in the uk.

 

[Ago37]

Hi guys, looks like I have struck some luck with DLC and found a company in the UK that will happily coat the rockers for me I just need to make sure that they are well polished to receive the coating.

As for the valve clearances I have my concerns as I have no record of the them being done, as I have mentioned the bike has covered 13k.

I think the best method is probably going to be... get the rockers sorted and then recheck the clearances then.

I am considering the mbp collets but on the site it appears the 4v option is out of stock.

 

[1fast750ss]

Option 2 on the collets:
MBP Retaining System Combination Shim Kits | Product Categories | EMSDUC

Depending on price, he also sells hard chrome rockers for $65 each with trade.

 

[tye1138]

I'm sure I had checked them correctly I panicked as the clearances where practically nil. When looking in the SPS handbook they seemed miles away from the quoted ranges. From memory I think an intake unloaded was something like 0.11 to 0.24... Don't quote me on that.

Your right, they should be around .11 - .18mm, thats the range.

I'd pop the half rings out first and examine them. If they shifted, the opening shim could be propped up by it and NOT sitting on top of the valve stem. As a test, you can remove the closer shim, put the opener shim resting on top of the valve stem (where it belongs), put the cam back in it and re-measure. If it measures out the same, then you've got substantial wear on the valves/valve seats. If it measures out differently, you've simply got screwed up half rings. New half rings (which are cheap) could solve your problem entirely.

I've been in many bikes where the clearances were shot, just to find the half rings were messed up, it happens.

 

[Ago37]

Many thanks guys this advice is seriously valuable as I have been reading and reading trying to make sense of the situation with my bike.

I think the half rings is a great shout and think I will purchase a full set of new half rings and re try the shim gaps.

As for the DLC I have been put into another conundrum after reading a thread on Speedzilla, commenting that coating a poor initial surface will not fix the problem as it will still compact... flake and bugger up...

I know the only real answer is to replace but I am loathed just to give up.

 

[tye1138]

Unfortunately, I have a feeling the half rings are fine. My guess is, your problem relates to soft seats and valve mating surfaces which are worn out. Running closers very tight can cause this problem and I surmise, you're probably barking up a major service bill unless you can determine WHY the clearances changed so radically.

There are two thoughts to this problem. One is to simply fix the issues with some re-shimming/half rings AND used rockers from ebay or something. It won't cost too much, the parts are radially available. But then you'll be paranoid about the future of the motor, so its a toss up. Both of my 748 motors self destructed before I had spent too much money re-building them. I replaced all the rockers with used ones from a friends shop and they all slowly went bad. It was depressing to see happen in front of my eyes and I couldn't do anything about it. Lucky for me, my bottom end on BOTH motors was toast, so the solution was quite simple… part the bikes and buy something else.

The rockers were fine after production date 8/01. So that means some 998's have the same problems and some don't. Unfortunately, you can't put a testastretta into that old 748 frame with modifying it and buying LOTS of extra parts. So it leaves you with two options… part it or fix it.

 

[Ago37]

Hi guys!! It's been a few days since I last posted but have had some major developments in my camp. Pulled the motor down and stripped the heads and as expected about 10 of the rockers where ruined but the rest looked ok.

Went thought the process of recoat... Re chrome... Or Replace and have struck luck with two heads, barrels and pistons from a 2002 748 with a set of perfect rockers bar 2!!!!


I don't think the guy was aware of how much the heads would go for stripped down and got the whole lot for £150 .

I will now work through what I have and build her back up.

I have a couple of questions for you guys:

When pulling the heads the barrels are stuck hard and fast and have not needed to be split for what I am doing. Could the heads and barrels be refitted without parting and replacing te head gaskets as the bond has not been broken?

Also would the valves be the same in a 748 bip and 748sps?

Having all the duplicated parts now means fingers crossed she will be better than ever and all for the cost of one new rocker from Ducati .

 

[1fast750ss]

Keep in mind, the heads are completely different. The '02 heads are unique in that the testabasso heads require a different belt, so maintain the original SPS heads.

That said, IIRC the valves are the same diameter, however it's the cams(as you know) that are the big difference there, and the exhaust valve stem length is shorter in the '02 heads.

 

[tye1138]

Just swap the rockers between the two heads.