Very bad blow by - Help!

[Ducdude]

Do a compression/leakdown test and make sure you haven't stuck a ring or had a piston seizure before you start buying extra breathers, etc..
Cheers, John

Thanks John. Compression test yielded 152psi on the FT and 154psi on the rear 3 months ago so things may have changed in the last 300miles..These were the first 300 in 40 years after sitting unused in cellars and barns. A proper leak down test is coming but at 194lb.s/86kg/ 13.5stone it takes 7-15 seconds for the kicker to drop me down from the top to the bottom of the kicker's stroke with me starting the motion by bouncing my weight a bit. I have no idea if this is good or not but I have the feeling it is not..Call it intuition.. So how long should it take the kicker to lower me down? Bike is a 52 Shadow
Thanks,
Eric

 

[Albervin]

Really depends on what is inside. My '48 Rapide will support me on the kick start for at least 8 seconds on both front and rear. I may go out there with a stop watch now and I may be some time...

 

[Black Flash]

I had a chat with Bob Dunn the other day and of course we were also talking about breathers. First of all the engine has to be in a good condition with no blowby leaks for a start.
He told me the following: the longer he works on these engines the more he appreciates the fantastic design work by the two Phils.Over his mayn years of repairing these engines he went many differnt ways but very often came back to the original design, just with optimised clearances. And a Vincent was not a bike built like todays bikes but was matched and hand assembled from a start. Bob reckons that the standard breather is absolutely up to his task and yet can still be approved.
everybody with some skills should be able to file the opening as supposed in the literature. if you have access to a lathe turn down the outer diameter of the sleeve in the slot area, especially on a Comet where the breather spindle is inside some kind of a housing ( I don't know if that is the case on a twin out of my mind). He suggest checking the timing with a little tube connected to the outlet and sucking while slowly turning the engine.
If somebody with the reputation of Bob Dunn says the breathers is ok as is, there is no reason for me to doubt.

 

[Albervin]

I think the devil is in the detail. If all is as per standard then I agree. However, tolerances, bodges, "improvements", different materials and a host of other parameters lead to the problems we face.

 

[timetraveller]

Just a quick addition to Black Flash's contribution above. I suggest blowing rather than sucking, just in case there is something loose in the pipe which, if it is there, is something that you certainly will not want in your mouth.

 

[Black Flash]

I agree with timetraveller, sucking could give vincenteering a strange taste

 

[Ducdude]

Well, today I got the equipment for the leak down test and had at it...

The front cylinder had 6-7% leak down with zero noise at the valves not a bad value for a 60 year old engine.
The rear cylinder had 17% leak down with a bit of the air escaping from the head gasket between the cylinders about center between the studs..

This equipment (snap on) indicates that anything greater then 12% requires attention. So it looks like the front is good.

This was done on a cold motor at 52F/11C in damp conditions..

So here are today's litany of questions:

1. With this data in hand and a compression test yield of +150psi Ft and 140+/-5psi rear what does this say about the condition of the top end?

2. Could the head gasket leak (small as it is ) contribute to the abundance of crank case pressure, that is blowing out all my seals and oil?

2.1 If it is not blow by pressurizing the crank case and the breather is timed properly as shown by the blow method. Where else could the abundance of case pressure be coming from...(I will be retesting the timing of the breather in case it has shifted...)

3. While replacing the head gaskets would be the best thing to do to fix the leak, I would like to wait till winter to do that. What are the feelings about just retorqueing the heads to pull up the leak?

4. If I am going to tighten up the head bolts is there a "proper Method" to do so? If so what is it?
What are the head bolt's torque spec.?
Should I just loosen each one 1/2 turn and then bring it up to spec in a Chris cross manner across the head?

5. To tighten the head bolts do I HAVE to remove the UFM or can I do it while attached?

6. I am guessing but I would think I would have to loosen all the engine to UFM bolts that hold down the frame mount bracket before I could do anything with the head bolts? Correct?


Any other tips, pointers, recommendations or criticisms welcome.

Thanks Much Gents....

Cheers,
Eric

 

[mercurycrest]

Eric,
There are no head gaskets, it's a lapped fit. The heads are torqued to 35ft. lbs. You can check and re-tighten the heads with a crow foot spanner on a torque wrench if you loosen the double nuts above the head brackets. BUT... and it's a big but, it's not uncommon for the lip on a loose liner to break and that could be the cause of your blow-by problem. My suggestion is that you find another Vincent owner near you who can tutor you through the basics of taking a Vincent apart for the first time. It's a very user friendly bike and you can fix all your problems and have the bike back together in an evening or two, but you need to know the proper order of doing it.
Cheers, John

 

[b'knighted]

Hi Eric,

Look also at the comments on Buzz's thread. If Alan & Trevor are correct (and who am I to disagree) you are at the start of at least 15 years of enjoyable mucking about. While John is correct and you may get the bike back on the road within a couple of days, I'd recommend not pulling it apart too soon. Fit a BIG bore breather with a non-return valve in the ATD cover area and ride this season. When the weather fails you can pull it apart with time to get any replacement parts and rebuild without losing the pleasure of your first riding year.
If the head blow is between studs, re-torquing the nuts is unlikely to help.
If you can access MPH451 page 10 there is an article on breathers by Derek Sayer. It includes a good description of the Mac Read breather system, which I cannot recommend highly enough. I believe he based the nylon ball valve on something used by Ducati. Using stainless tube instead of rubber could improve its appearance.
You can find this article by word search on WitakerPedia.
https://www.voc.uk.com/net/docs/3.5f/3.5-451-10.pdf

Cheers,

 

[Ducdude]

Thanks all for your input...

I will give snugging down the head a try and see what that gets me. I will know in a few hours.. I will also be fitting a D breather with a very slick one way valve to see what that gets me as far as breathing benefits.. Step by step I will figure this all out...I just want to ride her more then 50 miles "at speed" and not worry about washing a pint of oil off the out side of the bike and off the tyre..

We are getting there..

Thanks,
Eric