Mercury XR4 question

**dlivewyer** · 03-18-2018, 08:44 PM

Has anybody ever seen one of these motors with only 90 lbs of compression on all cylinders? I had one and it had 120+ on each cylinder.

My cousin just bought this motor. It runs great once it warms up, but man, what a bear to start and warm up.

I think it has been rebuilt and has the wrong heads on it or thicker head gaskets than stock.

What say you?

**91eagle** · 03-19-2018, 01:42 AM

May just need a set of rings ...but slap a set of stock head gaskets on it and see if it was running thicker ones ....as fas as the idea of it having heads other than stock ....find the casting number on the heads and post it here I'm sure someone here will let you know if there the correct heads for it

**mach351** · 03-19-2018, 05:47 AM

Check it with another gauge....

**91eagle** · 03-19-2018, 05:55 AM

Originally Posted by mach351

Check it with another gauge....

Good idea he has id suck to build a motor cuz your gauges off 30 lb

**Motv18** · 03-19-2018, 06:34 AM

Maybe incorrect testing? Did he bump the needle 3-4 times or crank it till it wouldn’t go up more?

**dlivewyer** · 03-19-2018, 06:48 AM

It has been tested with 3 different gauges and all 3 read the same thing. If it needed rings, what are the odds that all 6 cylinders are worn equally and compression has deteriorated uni formally?

**rock** · 03-19-2018, 07:36 AM

I can't imagine all 6 holes being down due to wear but spose anything is possible. It could have a set of uncut 2.5 heads on it with 1.25 gaskets. I have ran 2.5 heads (cut) on a 2.4 many times before but usually have to shave a bit of the width for them to fit which would show on the exhaust side of the head unless they were painted afterwards. If they are 2 piece heads ignore this post.

Rock

**Krazymaan** · 03-19-2018, 08:52 AM

Hard to imagine anyone would put extra thick gaskets on a 2.4 with stock heads and stock motor. probably just tired, had a bad water pump now and then creating hot cylinders cracking a ring possibly.

**tlwjkw** · 03-19-2018, 09:03 AM

never seen thick and thin 2.4 stuff... least not available to tha public?.. not even tha "fat block xr4"?.... had a bp that went down ta 80/85 lbs on all after beatin' tha **** outta tha thing for several summers.....

**rock** · 03-19-2018, 09:55 AM

[QUOTE=tlwjkw;3029070]never seen thick and thin 2.4 stuff... QUOTE]

Been workin on 2.5 stuff too long I guess. I just assumed you could get either. I could still see a 2.5 head easily causing lower compression.

Rock

**dlivewyer** · 03-19-2018, 10:23 AM

I think I'm going to have to get a leak down tester, my curiosity is killing me.

**tlwjkw** · 03-19-2018, 10:26 AM

"I could still see a 2.5 head easily causing lower compression."

yeah, there are a few of those out there now days.. don't really understand tha reasoning behind it though unless that's all ya got ta work with... even saw where someone actually cut center mains onna bp efi front half ta use onna 2.5 block.. don't see how that will work out though?

**billybob** · 03-19-2018, 10:45 AM

I would try POWERTUNE before disassembly, It might be carboned up, that might give good indication of possible problem.

**mach351** · 03-19-2018, 11:11 AM

I guess my next question would be if it’s turning over fast enough. Battery going south? Like said earlier, every hole worn the hell out is possible, but unlikely.