Perkins 4108 Compression

CalicoJack said:
Does anyone know what readings I should be getting for a 4108 on a compression test? Mine are 245lb , which seems quite low.
Thanks
Nigel
Click to expand...

As they are all the same and assuming it starts okay and doesn't seem down on power, then I wouldn't worry.
Worn bores or leaking valves would give varying readings across the cylinders.

My 4018 is 33years old and still going strong although I've never checked the compression pressures as it starts easily. I did overhaul the cylinder head and chek for bore wear 2 years ago and was suprised how clean and un worn it was.
 
CalicoJack said:
Not starting as well as is used to
Click to expand...

Have you eliminated air leaks in the fuel system?
The previous owner of mine had had starting probs which were worse when it was hot. I think he spent a lot of time bleeding the system but never found the cause.

In fact I found several air leaks, mainly due to the rubber seals on the return pipes unions. I replaced all the seals - lift pump, return pipe, injection pump inlet and outlet - haven't had a problem since.
Also make sure the return pipe from the fuel filter to fuel tank loops upwards at the filter, before dropping down to the tank.
 
gordmac said:
Not really as simple as 22x14.7.
Click to expand...
You're right.
It's not that far out in practice, and I can't be arsed to go into all this (dynamic compression ratios) - the pressure you measure with a tester by cranking on the starter is always lower than when it's running. If I get the chance when I'm next down at the boat I'll try and measure mine as a comparison. I suspect it might be lower.
 
Last edited:
You must log in or register to reply here.

Share this page

Top