head gasket life?

[Rversteeg]

I bought my 98 940LPT in 2000 when it had done a little over 110K miles. Since then I had the timing belt replaced every 50K miles, but I never went back to the workshop for retensioning nor did I do it myself. It must now be on its 8th belt with at least the last 6 belts never having been retensioned, so I am not too worried about this recommendation.

According its service history the previous owner had the cylinder head replaced at around 100K as one of the valve shims approached the Volvo specified minimum value (running on LPG). Volvo specifies a quite generous minimum thickness and I have taken the replacement head much further now by using thinner shims without a problem. It is now nearing 430K miles, still on the second cylinder head, so the current HG is now in for 400K miles.
From other owners I understand that the original HG generally lasts around 200K miles.

[Laird Scooby]

Originally Posted by Rversteeg

I bought my 98 940LPT in 2000 when it had done a little over 110K miles. Since then I had the timing belt replaced every 50K miles, but I never went back to the workshop for retensioning nor did I do it myself. It must now be on its 8th belt with at least the last 6 belts never having been retensioned, so I am not too worried about this recommendation.

According its service history the previous owner had the cylinder head replaced at around 100K as one of the valve shims approached the Volvo specified minimum value (running on LPG). Volvo specifies a quite generous minimum thickness and I have taken the replacement head much further now by using thinner shims without a problem. It is now nearing 430K miles, still on the second cylinder head, so the current HG is now in for 400K miles.
From other owners I understand that the original HG generally lasts around 200K miles.

The suggestion from that is that LPG is much kinder to engines (and certainly the environment in general) but the reason for the minimum shim thickness as i understand it is so the cam can't flip the shim out.

[griston64]

I've just removed the head from my B230fk which was original on 230k

The timing belt was 18 years old with 130k on it. The plug gaps were all 0.9 and the distributor cap was cracked. Add to that the pcv was blocked solid. And it looked like the oil was about 20 years old .Funny thing is it ran like an absolute dream and idled as smooth as silk !!!

[classicswede]

Originally Posted by griston64

Pretty certain the standard head bolts are the stretch type on a 940 and new ones should be used every time. Three stage tightening 20nm,60nm and angle tighten 90 deg. Clean threads and oil bolts. No mention of re torquing

They can be used many times over provided the bolts have not stretched


18psi is not big boost but I would go with 12.9 high tensile bolts or studs rather than the factory bolts

[griston64]

Originally Posted by classicswede

They can be used many times over provided the bolts have not stretched


18psi is not big boost but I would go with 12.9 high tensile bolts or studs rather than the factory bolts

How would average Joe know whether they have stretched or not ?

[Laird Scooby]

Originally Posted by griston64

How would average Joe know whether they have stretched or not ?

Stretch bolts stretch so should always be renewed.

[Clan]

Originally Posted by griston64

How would average Joe know whether they have stretched or not ?

There is a narrower section half way down the bolt , if it looks waisted change it . I have not yet seen one which is , Maybe overtightening will do that. The manual says use the bolts a maximum of 5 times .

[Rversteeg]

The suggestion from that is that LPG is much kinder to engines (and certainly the environment in general) but the reason for the minimum shim thickness as i understand it is so the cam can't flip the shim out.

A petrol engine is not optimized for running on LPG. The usual mixture enrichement at high loads is even unwanted as the cooling effect of a rich petrol mixture is absent when running on LPG. A rich LPG mixture will actually even burn hotter than a stoichiometric or lean mixture. Also the slower burning of the LPG mixture at higher speeds could mean in some cases that the exhaust valve is already opening before the combustion is fully completed. This all puts a higher thermal load on the exhaust valves causing a continuous receding of the valve clearance. I am now quite experienced in changing shims...

You have reached the minimum shim thickness when the shim no longer sticks out of the bucket, around 3.0 to 2.9 mm thickness. f you go beyond you risk damaging the camshaft as the cams will then hit the top rim of the bucket. Obviously taking the max out of a cylinder head was not anticipated by Volvo and I can imagine that they took a much bigger margin.
I do not think there is a risk of thinner shims flipping out of the bucket, as the (considerable) force needed to pry them out of the bucket does not depend on thickness.

[deeman940]

Originally Posted by Laird Scooby

Because you didn't do the job yourself, don't know what sort of bolts were fitted. Early 940s had normal bolts that do need retorquing, later ones don't as previously mentioned. You really need to find out which you have.

As for timing belt retensioning, it's more common than you think.

For example, on my other beast, there is a special blue timing mark at ~18deg ATDC and that is where you intitially set the tension. Then you turn the engine over 2 turns by hand and check everything still lines up. If so, you start the engine, let it idle until hot, switch off and allow to cool. Then turn the engine to the blue mark just after #1 TDC and release the tensioner locknut and let it retension, tighten the locknut. That's it for the next 96k miles.

However on the redblock it has to be after 600 miles, timed at TDC #1, slacken the tensioner locknut and let it retension then tighten the locknut again. If memory serves that's it for 40k miles (early square toothed belt) or 50k miles (later rounded tooth belt) but the wise owner will use 36k and 48k miles respectively.

As for my 760, that's never had a timing belt!

i did order the bolts. they were the Elring stretch ones

[griston64]

Originally Posted by deeman940

i did order the bolts. they were the Elring stretch ones

According to parts catalogue all 940's from 1990 to 1998 used the same stretch head bolts. Part number 1306341

And suggest one use only https://www.skandix.de/en/search/?q=1306341