Race Engine Forum UK

Hello Guy,

Regarding the head gasket issue as I have reported (via e-mail) prior to becoming a member to the forum, could you please help and educate me on the head gasket's internal bore diameter ?

I am confused about the size of the cylinder bore diameter ( which is 85 mm in my case ) VS the head gasket ( which is 84 mm ).

As you know, even though I have been building and looking after other make of engines ( mainly Ford Pinto and YB, Mitsubishi EVO, Opel CIH ) I do not have any experience with the Fiat engines. Therefore, I would very much appreciate if you could educate me up to a level which I could successfully run a very professionally built GC engine.

Due to the fact, we had the blown head gasket, I would like to check the conrod bearing on that cylinder and the piston ring. At this stage, do you advise to fully strip the engine to inspect and/or replace all the piston rings ( it was still a very fresh engine prior to the incident - bores still seems very very fresh )

Also, as you have strongly recommended, my customer' s gravel rally car 131 need the sealed airbox unlike many other examples of the typical 44 IDF air filter systems ( like the ITG or KN ). However, so far I could not identify the proper sealed airbox for our gravel rally car application. Probably, an off the shelf airbox system does not exist to fit on to our engine in 131 but any help to build ( or source ) the required sealed airbox would be great.

I would like to take this opportunity to wish all the members a very happy new year !!!

Regards,

Kerem

Greeting to you also Kerem


The gasket fire-ring bore in your case - uncompressed/undistorted by detonation - is 85.20 - 85.50mm, slightly bigger than the bores. Although the pistons were run flush the crown has a 1.5mm radius so there is no chance of contact. I have used this setup a hundred times. You can rule out gasket bore as cause of failure.

There is no sealed ducted airbox available - you will have to make one.

G

Hello Guy,

Thank you very much for your help. It is apparently my misjudgement about the bore size of the cylinder head gasket. Since it is distorded I might have measured incorrectly. However, I would still like to send the gasket to you for your inspection if you accept.

Meanwhile, I would like to get the new gasket and possibly a set of con rod bearings and a set of piston rings.

Do you advise me to strip the engine ? Would you like to see some photos ?

I am planning to design and build an alloy airbox which will have an entry for a 2" hose. Of course, I will leave at least 1" gap at the top of the trumpets. However, I am not sure about the width of the airbox.

Regards,

Kerem

First post a good (clear) photo of the gasket please.

Judging by your description of 'crimped' it's a detonation failure like the attached (sorry not a brilliant photo but you can se the gasket looks like it has been crushed all round the fire ring with pliers). In that case the bearings and pistons need to be checked - by removing the pistons. Remove the sump and unbolt the rods - clean the top of the bores with fine Scotchbrite and slide them out. If there is no ring or bore damage they can just go straight back in although I would renew the rod bearings as a matter of routine. No point second-guessing what else, just report what you find.

No point looking for a stronger gasket, if the gasket doesn't burst the det pressure will just find something else to 'attack' (rings and piston)

The airbox needs to be 1" clear all round of rampipes so it's cross-sectional area just needs to be big enough to mount to the carbs and allow 2" duct - like the attached.

Thank you very much.

I will post the photos of the gasket. I will send you an e-mail for the parts.

The airbox photo and the details is very helpful. I will be able to produce an airbox for the IDFs.

Regards,

Kerem

Some photos of the blown cylinder head gasket.

Hello Guy,

I am sorry, I think I could not manage to upload the photos correctly. May be, I should save them smaller first then upload. If you like, I can e-mail them as well.

Regards,

Kerem

1st photo says it all. Classic detonation - distorted/ruptured and dislocated fire ring, scorched piston.

GC

Thank you for your reply Guy,

I think, I should proceed as you explanied above. Next week, I will share my findings of the internal parts. ie. Rings, piston, cylinder bore and the bearings.

Have a good Sunday,

Kerem

Barely recognisable as the GC engine that left my works mid 2011,

covered in corrosion, no coolant additive (brown water everywhere), toothed belt water pump drive missing .....


GC

Exactly. They changed the pulleys and engine does not have the toothed belt system any more. Including crankshaft pulley all the pulleys have been changed. I can only assume that, this is what Evren's mechanic did during the installation. As you know, then the car has been sold. Now, I convinced the new owner to correct everything on this engine. I explained him about the original built quality of a GC engine.

Why did they do that Kerem?

G

I wish I knew. I will investigate why they have removed the toothed belt system. At this stage, I do not want to comment on that !!!!
Just like the throttle linkage which was gone !!!

Regards,

Kerem

Hello Guy,

Now, back to work after some traveling.

After some investigation, they told me that engine kept snapping the toothed pulley belt system ( twice ) then they decided to change the system to the standard belt system. Apparently, the system that they removed has been lost during the owner change overs. So, we do not have the toothed belt system as of now.

I dismantled the engine and I am now posting the photos of the Nr.1 piston. As far as the vertical scratch marks goes on the skirt of the piston, same situation applies to the other 3 pistons as well.

Conrod Bearings seems absolutely fine but I would still like to replace them.

Cylinder bores seems in a very good condition in general, still honing pattern is very visible. However, I found a very strange " valley " in the Nr.2 bore. The valley is on the exhaust side and 5 cm below the deck. It's dimensions are 0.70 mm diameter and approx. 0.30-0.40 mm depth. I am also including a close up photo of my finding. ( also 1 photo from a distance )
There is no other marks next to this valley and it seems that it has somehow appeared there.

I can send you the Nr.1 piston for your inspection in order to decide if we can still use them with this rather heavy scratches on the skirts.

Regards,

Kerem

Kerem please use Pixresizer and edit those gigantic photos down to 500kb.

Details in Readers' Cars top level - 'size matters'...

Belt kept snapping? Good grief. Probably never sealed off the underside with an undertray, stones can snap a cambelt never mind a little alternator one. What a bunch of amateurs they are.

Those pistons don't belong back here they belong in the bin.

No idea what that bore damage resulted from. Probably ingested a stone or something.

What an awful mess.

G