Hi all,

I had recently had my MC21 engine fully re-built.

I had the mechanical water pump seal (19217-KV3-831) replaced as a precautionary measure during the rebuild.

Once the engine was re-installed and running, it leaked coolant from the inspection hole on the RH side of the casing - a single drop every few blips of the throttle - which i know points to a faulty/damaged seal.

I removed the casing and impeller shaft and realised there was some corrosion on the impeller shaft - not loads, but enough that it needed to be rubbed down with some fine wet and dry to be totally smooth.

When i re-installed the impeller and ran it, it leaked again, as bad if not worse.

I spoke to the guy that built the engine and he said the seals can need to 'bed in' after some miles of use.

I am not sure i agree? Has anyone had any experience of this seal leaking when installed and whether they need to bed in, or settle in any way after multiple heat cycles or a few proper miles?

Personally i suspect the small amount of corrosion has damaged the seal, but before i bin it and buy a new one and strip it down again etc, i wanted to ask if anyone had any thoughts/experiences?

Any ideas very much appreciated.

Thanks,
Max

20 views and no replies... should i take that as no-one had heard of the 'bedding in' before and I should just replace the seal??

Knowing the water pump seal can be problematic, i thought someone might have a POV one way or the other?
(exact same seal in my CRM250 and they can cause cause issues too)

Any thoughts welcome.

Even if just ti tell me stop talking nonsense!

maxhouse wrote:20 views and no replies... should i take that as no-one had heard of the 'bedding in' before and I should just replace the seal??

Knowing the water pump seal can be problematic, i thought someone might have a POV one way or the other?
(exact same seal in my CRM250 and they can cause cause issues too)

Any thoughts welcome.

Even if just ti tell me stop talking nonsense!

Here a view and replie.

I changed my mechanical seal on my mc16 because it was leaking to, the same way as it came out,and its was leaking again.
The problem was the first owner installed it not correctly,placed the seals in the good direction and the leaking was gone, not a single drop .
And bedding in its possible but it looks to me as a ferrytale, but thats my opinion

Sounds like he is fobbing you off, no way a seal needs to bed in!

Stupid question but it is water and not oil, there is a standard rubber seal that seals the gearbox which sits behind the mechanical seal.

The water pump seal has three parts, the metal body that sits inside the case, a flat seal that presses into the back of the impeller itself and the main seal with the spring in it. The main seal seals against the metal body and the rotating impeller, the spring puts pressure on to the part of the seal that mates with the impeller (this is hard to explain but is quite obvious if you are looking at the parts)

The only part of the impeller shaft that has to seal is the section that runs in the gearbox oil seal, if you have oil not water leaking then it is either this shaft or the oil seal that is the problem.

The area of the shaft that normally corrodes is the part that sits inside the mechanical seal, if it is corroded I would say it is a sign that the seal has been leaking previously.

If it is definetely water coming through the hole it must be either the seal is damaged ( unlikely if it is a new seal) the flat seal that presses into the back of the impeller is either damaged, was damaged previously or is not seated correctly ( on the piss) in the back of the impeller or the metal body has not been replaced and was damaged/worn previously or the new part has been damaged on installation.

From my previous experience of changing these my money would be on the metal body being damaged on instalation, this part is thin gauge sheet metal and actually quite delicate, it only needs some monkey hitting it a bit to enthusiastically to knacker it. I speak from experience

Either way I would be having a word with the guy who changed it.

Thanks both for the replies.

In relation to the comments above.

It is definitely water leaking - clean water, no oil at all.

When i first got the bike, i never really ran it - it had various issues and was stripped down immediately, so was not aware if there was a leak or not. However, as you say, the previous seal must have been leaking to some extent as the impeller shaft was corroded.

I removed the various seal parts from the clutch casing on disassembly, so know what parts you mean.

All parts of the new seal assembly have been replaced, and are genuine Honda.

I will re-check the installation of all the components, as if i am very lucky one of the seal is not seated correctly.

I agree that the metal part of the seal is very delicate and could very easily be knackerd on assembly. I am not sure how best to confirm this though?

Another niggling doubt is that the impeller shaft has just enough corrosion damage to not seal properly.

There is very clean looking impeller shaft on eBay that i may have to take a punt on, otherwise i could replace the (expensive) seal assembly and see no improvement?

Hmmmm - decisions decisions?

I will report back. Thanks again!!

New seals don't need bedding in. That's a cop out for sure!

The problem that will crop up over time is the oil seal wearing a groove in the shaft, and of course the oil seal itself wearing. In either case you'll get oil dripping from the telltale hole.

As for the mechanical seal. These seem to last a very long time, but when they go bad they cannot be salvaged. In the case of a bad mechanical seal you'll see coolant dripping from the hole.

Replacing the just the oil seal is a non starter as you must remove the mechanical seal to remove the oil seal. Bit of a pain, but that's the way it is. And removing the mechanical seal will surely destroy it, so that'll need replacing too.

Clean up the seal housings prior to refitting the new parts. They're generaly pretty dirty and you don't want to mess the new seals up when you pop them in.

The oil seal is pretty straightforward to fit. Can almost press it in my hand. Just make sure that it's nice an flat once installed. Note the correct orientation of the old seal before you press it out so that you get the new seal in correctly.

The mechanical seal needs a bit of precision to press it in. It's possibly to distort the shape of the steel housing if not pressed in squarely, so proceed with a little caution. I only ever do this on the hydraulic press, so that I know for sure that it's perfect.

before fitting the shaft, make sure that there's no roughness to the shaft where it'll meet the oil seal. Don't want to destroy the new seal before you've even got to the end of the road.

Once the impeller is all tightened up there should be a lot of drag when turning the shaft. This is actually a good way of deducing the condition of the mechanical seal. If it's easy to turn then it's probably on it's way out. Very similar to the center crank bearing on an MC21/28. If you can spin it, it's dead!

Hope that's helpful.