Gilera 150 head gasket.

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ivor
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Gilera 150 head gasket.

Post by ivor » Mon Jul 13, 2015 4:36 pm

Hi all, the Gilera 150 Sport I have been working on is nearly finished, though I do still have electrical problems! However, the purpose of this post is to ask about the head gasket. I used a new one, the head and barrel seemed quite flat, and I tightened down the head tight.
But, after running the motor, I have found much oil dripping down from the head/barrel joint. I have lifted the head, and the entire surface of the gasket is covered in oil, although the gasket seemed not to blow around the piston. Neither is the bore particularly oily.
I have used two small rubber 'O' rings around the top of the stud in which the oil is fed to the rockers. This all seems to work well with plenty of oil going to the rockers. It would seem that the head joint is not tight enough, and the oil running back down the pushrod tunnel is seeping into the joint.
Can I get away with re-using this head gasket if I use a sealant, and tighten it down well ?
And does anyone have a torque setting for the head nuts ?
Thank you all in advance.

nrbgilera
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Re: Gilera 150 head gasket.

Post by nrbgilera » Sat Jul 13, 2019 11:17 am

Hi, I am new to the forum, and have just seen your post regarding oil leak from the cylinder head.

I have the same problem, did you manage to sort it out. I have just rebuilt my 1958 150 sport engine, and it runs ok, but, oil leaks from the front of the head to cylinder joint. I have re-tightened the bolts to 25 Nm, but it still leaks. the torque settings are standard for 8.8 grade M8 bolts, I do not have any specific information for the Gilera, does anyone have the correct settings. I have a new gasket, but don't want to fit it yet until I understand what is causing the problem. As you describe, when the head is removed there is oil all around the gasket, but not in the bore. it is as though the head is not tightened down enough, but I dare not tighten it more. Also, you refer to a 'O' ring, there was no 'O' ring when I dismantled the engine, where is the 'O' ring located ?

Hope you may be able to help

Neil

lambs
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Re: Gilera 150 head gasket.

Post by lambs » Thu Jul 18, 2019 11:27 am

The OP hasn't been active on this board for going on 2 years but perhaps you could try here for a manual that will help with some info:

http://www.rpw.it/Documentazione.htm

I don't have any experience with the early Gilera engines (50's or so), but are you sure the head/cylinder studs are 8mm ? My 150 Autostrada and the 202 engine both have 10mm studs with fine thread (ie M10 fine) for the retaining nuts. My manual says to use 5kgm (49Nm or 36ftlb) for those nuts. For 8mm nuts the manual says to use 4kgm/39Nm/29ftlb. I always tighten studs like this progressively (ie incrementally increasing torque to the final recommended value) and in a criss-cross pattern.

The fact that the entire head gasket is covered with oil perhaps suggests oil is leaking down the head studs, maybe due to incorrect torque (??). That assumes that the contact faces are all in good condition, of course.

The o-ring referred to is perhaps the one that seals the end of the hollow (drilled) stud that feeds oil to the rocker gear via drillings in the rocker cover.

nrbgilera
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Re: Gilera 150 head gasket.

Post by nrbgilera » Mon Jul 22, 2019 10:08 am

Thank you for the reply, and the information.

I have refitted the head with a new gasket, and tightened again to 25 Nm, as the studs are 8 mm, and as I have no Gilera info on torque settings, I used standard 8.8 grade 8 mm torque settings which states 25 Nm. I have run the engine, and the leak has stopped, but I am interested in the torque settings you refer to. My 'chart' states for 8 mm 10.9 grade bolts, 35.5 Nm, which is close to what you say. Maybe the bolts are grade 10.9, or better, I don't know. I would like to tighten the head further, just to be sure, maybe I increase to 30 Nm to be on the safe side, unless I can be sure the stud material is suitable for a higher torque.

Neil

lambs
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Re: Gilera 150 head gasket.

Post by lambs » Sat Jul 27, 2019 2:11 pm

A grade 8.8 bolt is not regarded as 'high tensile' being only about twice the UTS of a mild steel bolt. Generally speaking, anything above around 150ksi is regarded as 'high tensile', while above 200ksi we are talking 'ultra-high tensile'. Given that the studs are required to cope with cyclic loading associated with thermal expansion as well as shock loading associated with combustion forces, I'd be very surprised if the studs weren't made using a 'high tensile' grade steel+heat-treatment (ie better than grade 8.8). Unfortunately, only a hardness test would tell for sure (well, aside from a destructive tensile test).

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