a curious thing ? on trimming the leg and enigne run in

jon and michie

jon and michie

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This might sound odd I don't know but towards then end of the last season I found that once on the plane with the trim tabs with the drive leg at -4 that if I raised the leg to +2 the speed would creep up from 3100 to 3400.

This is on a single kad300 dp-g drive with under 300 hrs on the clock

so a couple of questions - first one and main worry - would I be doing any damage to the universal joint between the drive and engine?
could the increase be the boat finding its correct plane and is quite normal??
what sort of hours use would you expect to see when the engine has been ran in ?
many thanks for any help
Jon
 
Isn't this just that you've correctly trimmed the boat (at +2) so that the hull drag is balanced by prop thrust allowing you to achieve WOT - assuming that the rated WOT for your engine is 3400. Put another way, at -4 you're pointing the bow down into the water a bit and ploughing a bit more sea than you need to. I can't see how this would unnecessarily wear the UJ because you're inside the normal range of trim adjustment.
 
Thanks Jimmy - I think the actual wot should be around 3700 but maybe wear and tear on the turbo and or any fouling could slow it down.
My main worry was the joint - but how far could I take it
After 2years its still a learning curve

Jon
 
It’s not worth worrying about - the correlation of trim guage with UJ joint life expectancy.
Because how sure are you it’s been calibrated correctly in the first place ?
Your -4 might equate to another’s +2 etc - identical boat just reassembled differently after a leg off job .

It’s not like taking your car to be put an a jig and laser wheel aligned to get manufacturers tracking specs.
Which visibly affects tire wear and sometimes handling .
 
Portofino - That's a good point
When i had the sea trial done the volvo engineers recorded 3700.
Then the leg was taken off for a new case
 
Hi
It’s just that you have seemingly trimmed the boat properly. This is what you are meant to do for optimum running.
0 position should mean the leg is in line with the hull. -4 would be the leg angled downward.
I used to have the leg down to get on plane then have it trimmed up as far as +5 or 6 to get the bow out the water reducing drag at any real pace.

My current boat runs really highly trimmed up. You won’t damage the UJ at all at those angles. All you will do is save fuel and see better performance. It’s all good.
 
The U/J goes through a lot more degrees of travel when you steer the the boat than it does with trimming and it doesn’ t cause undue wear. The U/J has a replace interval of 1000 hrs in normal use and assuming there is no water contamination. You will probably also find the steering is less twitchy now you have the bow trimmed up correctly.
 
spannerman said:
The U/J goes through a lot more degrees of travel when you steer the the boat than it does with trimming and it doesn’ t cause undue wear. The U/J has a replace interval of 1000 hrs in normal use and assuming there is no water contamination. You will probably also find the steering is less twitchy now you have the bow trimmed up correctly.
Click to expand...

Hi spannerman, out of interest, what does normal use mean in the context of when to change UJ? Are saying Volvo's recommendation is to replace every 1000 hours? Wouldn't an inspection of the uj be the deciding factor rather than just changing?
 
In my experience its mainly been commercial use that gets to 1000 hrs, pleasure craft often don’t get near those hours before the U/J gets changed because of water ingress or neglect. Obviously if it gets to 1000 hrs with no discernable wear then it can continue, its up to the owner, just that Volvo specify replacement at those hours on commercial applications for reliabilty. Especially as they no longer have a grease nipple so they are sealed for life meaning you can’t lube them during a bellows change as you could on earlier models.
U/J’s nearly always announce their imminent demise with rumbling and/or vibration when the steering is on full lock at idle, not to be ignored as it can also damage the intermediate shaft bearing in the transom and the input shaft bearing in the drive. The repair bill can mount rapidly if not seen to. Worst cases I have seen are where the U/J collapsed and the parts got slung out and damaged the transom housing and the front housing of the drive. This is very rare and only because the owner ignored the warning signs, but having said that I have jumped on board several dozen boats and noticed the rumbling noise from the stern as soon as I manouvered the boat from the dock and the owner was blissfully unaware of the problem!
 
Many thanks for the replies so far very helpful and interesting.
My next part of my question is when would you say my kad300 engine is/has been run in - it has just under 300 hours

Thanks again
Jon
 
jon and michie said:
Many thanks for the replies so far very helpful and interesting.
My next part of my question is when would you say my kad300 engine is/has been run in - it has just under 300 hours

Thanks again
Jon
Click to expand...

Yes.

People may say things like " its only just run in" but in practice all running is ( or was) is the pieces of the engine wearing slightly so it all fits together nicely.

I say was as car no longer require run in ( well they may but they dont tell you to do it anymore!) as engineering tolerances are now far more precise than fred on a lathe that in the main it it not required.

Also remember a car used to require varying rev ranges and limited time at full throttle for x miles - however a boat cant really have that. You can only choose not to thrash the total nuts off it - but if you are on the plane the thing will be delivering a significant % of it rated power with little real option.

https://en.wikipedia.org/wiki/Break-in_(mechanical_run-in)

Even in the "old days" run in was maybe 10 hours - so at 300 you are well away.
 
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