I Opened a Time Capsule Today

**croSSed** · 01-27-2025, 09:06 PM

I have a 1987 XR2 150. I bought it in 2008, and when I bought it it was obviously a low-hour motor. I ran the crap out of it until 2023 when I replaced the 2L block with a rebuilt 2.4L chrome bore 175. I'm having trouble with the 175 now, and if you want to read about it, go here:

https://www.screamandfly.com/showthr...bore-quesitons

One of the things I'm contemplating is cutting my losses with the 2.4 and just reinstalling this 2L and call it good. One of the alarming things with 2.4 was that #1 had been resleeved, and bored oversize, and when I took it down the cylinder and piston were all scratched up. It made me start thinking that maybe when I was running high and fast it wasn't getting enough water, so I took the starboard side head off my XR2 today to check #1. It was pristine. And, the reason for the thread title is that the heads have never been off this engine. I was the first person since the guy at the factory installed the heads to remove one. Now, #3 has a "divot" in the bottom of the piston, and very mild scrape marks on the cylinder wall under it. See the pics below. Does that look like a detonation mark to you? The mark was raised, and I considered filing it down flat, but then I risk getting piston shavings down in the motor. Also, it looks old because it is covered in carbon, and the raised edges don't look like any igniting was going on there. You can see in the #1 hole (last pic) the factory cross-hatch marks still present. Thanks for looking!

Click image for larger version.

Name: IMG_0265.jpg
Views: 83
Size: 407.3 KB
ID: 539868

Click image for larger version.

Name: IMG_0264.jpg
Views: 70
Size: 421.4 KB
ID: 539869

Click image for larger version.

Name: IMG_0267.jpg
Views: 62
Size: 421.3 KB
ID: 539870

Click image for larger version.

Name: IMG_0266.jpg
Views: 60
Size: 400.4 KB
ID: 539871

**skialot2** · 01-27-2025, 10:09 PM

Sure does look like detonation to me. Did you check compression before you pulled the head? With the scoring of the cylinder, it is probably down some.

**108** · 01-27-2025, 10:40 PM

It ate something. Look at the reeds.

**croSSed** · 01-28-2025, 12:00 AM

Originally Posted by skialot2

Sure does look like detonation to me. Did you check compression before you pulled the head? With the scoring of the cylinder, it is probably down some.

At the beginning and end of every season I take a comp reading to see if anything had changed. Nothing had. The marks on the cyl. wall are very slight.
"It ate something." That was my initial thought, too, but look at the head. The head is clean.

**pcrussell50** · 01-28-2025, 12:02 AM

Originally Posted by 108

It ate something. Look at the reeds.

That was my first thought, too. FWIW.

-Peter

**LakeFever** · 01-28-2025, 06:08 AM

Piston pin failure

**ChrisCarsonMarine** · 01-28-2025, 08:39 AM

Ring locator pin came loose and worked its way out,my guess,Chris

**rock** · 01-28-2025, 10:21 AM

My first thought also. Can't believe the ring did not turn and wipe out the cylinder completely.

Rock

**108** · 01-28-2025, 06:41 PM

2 liter pins on the starboard side are at 1 and 4 o clock if I remember right. Broken circlip which is unusual and wipes out the bore, reeds, it ate some thing or has been like that since new for whatever reason.

**croSSed** · 01-28-2025, 09:52 PM

Originally Posted by rock

My first thought also. Can't believe the ring did not turn and wipe out the cylinder completely.

Rock

How would the locator pin do that damage on the piston, but not touch the surface of the head?

Click image for larger version.

Name: IMG_0267.jpg
Views: 8
Size: 421.3 KB
ID: 539917

**skialot2** · 01-28-2025, 10:05 PM

Originally Posted by croSSed

How would the locator pin do that damage on the piston, but not touch the surface of the head?

I have seen worse pistons with no head damage.

**rock** · 01-29-2025, 11:53 AM

Way worse. I have seen chunks of the piston gone without a mark on the head. Had a motor on an STV lose a circlip allowing the piston pin to migrate into the cylinder wall and 'machine" a slot that nearly went completely thru the sleeve but the head was perfect.

Rock

**tlwjkw** · 01-30-2025, 11:21 AM

Originally Posted by rock

Way worse. I have seen chunks of the piston gone without a mark on the head. Had a motor on an STV lose a circlip allowing the piston pin to migrate into the cylinder wall and 'machine" a slot that nearly went completely thru the sleeve but the head was perfect.

Rock

rock, i had same thing ona BP several years ago... it was down on power so decided ta take a look..thats when i found it... when i say down on power it was at 'bout 100lbs per hole, includin' tha one that was "machinin' a slot same dia as wrist pin.... go figure...

**rock** · 01-30-2025, 01:16 PM

Just when you think you have seen it all....

Rock

**croSSed** · 01-30-2025, 02:36 PM

I really appreciate everyone's reply. My questions are just so I can learn, not to cast doubt on what you're saying. I'm not convinced that that isn't a detonation mark, and the pin is fine. Bear with me... The marks on the cylinder look way worse in the photo that they actually are. When I run my finger along that I can barely feel it. It would make sense to me that whatever caused the detonation there, and melted that spot on the piston (that's exactly what it looks like, like a spot of melt) would also have damaged the ring(s) under that spot, cause the scraping. It seems to me if the pin came out and, say, got stuck on the piston at that point causing a hot spot that melted the piston there, it would have damaged the cylinder way worse than that. I'm contemplating (when the dozen or so other tasks I have to do get finished) taking this motor down, and pushing that piston out to see what happened. Maybe I'm stupid, but if the pin is still there, I'd be good with just changing piston/rings, and reassembling. The other 5 holes look pristine. If the pin IS missing, I'd do the same thing. At the last comp check (the last time it was run) that hole was not down on comp. You're welcome to talk me out of this.