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treepd
treepd

Posted: Thu Sep 19, 2013 4:58pm

Post Subject: manifold

We recntly had a new head gasket fitted. About 6 weeks after the manifold fell off and sheered a couple of the bolts. We were told that it was due to the tick over being to slow causing vibration. Is this possible as I thought that the bolts would have been torquedcup. The boat yard charged us for the repair. it seems a coincidence that this happened so soon after the head gasket was replaced. Is it common for a manifold to fall off, or is it that it was not put on properly after the head gasket was changed

Tony-B
Tony-B

Posted: Thu Sep 19, 2013 5:01pm

Post Subject: manifold

Any chance of being told the make and model of the engine plus the idle speed if you know it? Tony Brooks

treepd
treepd

Posted: Fri Sep 20, 2013 8:20am

Post Subject: manifold

It is a BMC 1.8 Sorry i don't know the idle speed, would this not have been checked when the head gasket was replaced.

Tony-B
Tony-B

Posted: Fri Sep 20, 2013 9:14am

Post Subject: manifold

I had hoped to have found a manual for your engine on line but can only find one for a 1.5 but as they are exceptionally similar (if not identical) in the manifold area we can take that one as good enough. I wanted to know about the engine in case it was one with individual cylinder heads but it is not. The 1.5 gives a manifold nut torque of 15 ft lbs and that is not particularly tight. While I would hope that all the nuts were tightened with a torque wrench where a figure is given I would not be surprised things like manifold nuts were not and the fitter simply relied upon his experience. I know I have often done this in the past. There are some things that come to mind. 1. Manifold nuts and studs often rust up so any damage MIGHT have been done during the undoing process, not by over tightening. 2. The manifold (assuming its a Polar or Bowman) is larger and heavier than the automotive one, it is also stuck up in the air so it must present greater loads to the studs which would not have been enlarged during the marinisation process. 3 How flexible is your exhaust? If there is no flexibility then engine movement would strain the stud and a low idle speed could well cause the engine to move about more than usual. I would hope that your engine had a bulk ring fitted to the flywheel during the marinistion process (or a heavier flywheel). If this was not done then it would tend to jump about at idle in gear. I agree with you that the idle speed should have been set as part of the head gasket renewal. From memory the 1.8 should ideal at about 650 to 750 rpm, but to be sure give Calcutt Boats a ring and ask them. My own view is that if this has happened you need to check what special tools they used to torque up the head nuts. 3 or 4 of them are masked by the rocker shaft so need a social crows foot socket to allow them to be torqued up in the correct order. The head should also be re-torqued after about 50 to 100 hours running and that crows foot will be required then as well. The only way to correctly torque the cylinder head nuts if no crows foot is available is to strip the rocker gear down whilst fitted to the engine and I very much doubt that would be done. Tony Brooks

treepd
treepd

Posted: Fri Sep 20, 2013 10:24am

Post Subject: manifold

Many thanks for your help Tony, much appreciated

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